Initial 65C02 Support

First pass at adding CMOS 65C02 support for the following instructions
and addressing modes:

   * ORA (ZP Indirect)
   * AND (ZP Indirect)
   * EOR (ZP Indirect)
   * ADC (ZP Indirect)
   * STA (ZP Indirect)
   * LDA (ZP Indirect)
   * CMP (ZP Indirect)
   * SBC (ZP Indirect)

COPYING

@@ -1,6 +1,6 @@
 The MIT License
 
-Copyright (c) 2008-2013 Seth J. Morabito <web@loomcom.com>
+Copyright (c) 2008-2014 Seth J. Morabito <web@loomcom.com>
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the

README.md

@@ -1,9 +1,9 @@
 SYMON - A 6502 System Simulator
 ===============================
 
-**Version:** 1.0.0
+**Version:** 1.2.1
 
-**Last Updated:** 11 August, 2014
+**Last Updated:** 8 January, 2016
 
 See the file COPYING for license.
 
@@ -30,7 +30,7 @@ are always welcome.
 
 ## 2.0 Requirements
 
-  - Java 1.7 or higher
+  - Java 1.8 or higher
   - Maven 2.0.x or higher (for building from source)
   - JUnit 4 or higher (for testing)
 
@@ -58,6 +58,7 @@ memory.
   - `$0000`--`$DFFF`: 56KB RAM
   - `$E000`--`$FFFF`: 8KB ROM
   - `$FFD0`--`$FFD1`: Motorola 6850 ACIA
+  - `$FFD8`--`$FFDF`: Controller for SD cards
 
 ### 3.1.3 Simple Memory Map
 
@@ -102,19 +103,32 @@ Memory contents can be viewed (and edited) one page at a time through the Memory
 
 ![Trace Log] (https://github.com/sethm/symon/raw/master/screenshots/trace_log.png)
 
-The last 20,000 execution steps are disassembled and logged to the Trace Log Window.
+The last 20,000 execution steps are disassembled and logged to the Trace Log
+Window.
 
-### 3.6 NEW - Experimental 6545 CRTC Video
+### 3.6 Simulator Speeds
+
+![Speeds] (https://github.com/sethm/symon/raw/master/screenshots/simulator_menu.png)
+
+Simulated speeds may be set from 1MHz to 8MHz.
+
+### 3.7 Breakpoints
+
+![Breakpoints] (https://github.com/sethm/symon/raw/master/screenshots/breakpoints.png)
+
+Breakpoints can be set and removed through the Breakpoints window.
+
+### 3.8 Experimental 6545 CRTC Video
 
 ![Composite Video] (https://github.com/sethm/symon/raw/master/screenshots/video_window.png)
 
-This feature is highly experimental. It's possible to open a video window from the "View" menu.
+This feature is highly experimental. It's possible to open a video window
-This window simulates the output of a MOS 6545 CRT Controller located at address `$9000` and
+from the "View" menu.  This window simulates the output of a MOS 6545 CRT
-`$9001`.
+Controller located at address `$9000` and `$9001`.
 
-By default, the 40 x 25 character display uses video memory located at base address `$7000`.
+By default, the 40 x 25 character display uses video memory located at base
-This means that the memory from address `$7000` (28672 decimal) to `$73E8` (29672 decimal)
+address `$7000`.  This means that the memory from address `$7000` (28672
-is directly mapped to video.
+decimal) to `$73E8` (29672 decimal) is directly mapped to video.
 
   - Address Register (at address `$9000`)
   - R1: Horizontal Displayed Columns
@@ -127,18 +141,20 @@ is directly mapped to video.
   - R14: Cursor Position (High Byte)
   - R15: Cursor Position (Low Byte)
 
-Although the simulation is pretty good, there are a few key differences between
+Although the simulation is pretty good, there are a few key differences
-the simulated 6545 and a real 6545:
+between the simulated 6545 and a real 6545:
 
-  - The simulated 6545 supports only the straight binary addressing mode of the real 6545,
+  - The simulated 6545 supports only the straight binary addressing
-    and not the Row/Column addressing mode.
+    mode of the real 6545, and not the Row/Column addressing mode.
-  - The simulated 6545 has full 16 bit addressing, where the real 6545 has only
+
-    a 14-bit address bus.
+  - The simulated 6545 has full 16 bit addressing, where the real 6545
-  - The simulation is done at a whole-frame level, meaning that lots of
+    has only a 14-bit address bus.
-    6545 programming tricks that were achieved by updating the frame address
+
-    during vertical and horizontal sync times are not achievable. There is no way
+  - The simulation is done at a whole-frame level, meaning that lots
-    (for example) to change the Display Start Address (R12 and R13) while a
+    of 6545 programming tricks that were achieved by updating the
-    frame is being drawn.
+    frame address during vertical and horizontal sync times are not
+    achievable.  There is no way (for example) to change the Display Start
+    Address (R12 and R13) while a frame is being drawn.  
 
 For more information on the 6545 CRTC and its programming model, please see the following resources
 
@@ -147,7 +163,7 @@ For more information on the 6545 CRTC and its programming model, please see the
   - [MOS 6545 Datasheet (PDF)] (http://www.6502.org/users/andre/hwinfo/crtc/crtc.html)
 
 
-#### 3.6.1 Example BASIC Program to test Video
+#### 3.8.1 Example BASIC Program to test Video
 
 This program will fill the video screen with all printable characters.
 
@@ -170,9 +186,9 @@ Maven will build Symon, run unit tests, and produce a jar file in the
 `target` directory containing the compiled simulator.
 
 Symon is meant to be invoked directly from the jar file. To run with
-Java 1.5 or greater, just type:
+Java 1.8 or greater, just type:
 
-    $ java -jar symon-0.9.1.0.jar
+    $ java -jar symon-1.2.0.jar
 
 When Symon is running, you should be presented with a simple graphical
 interface.
@@ -219,7 +235,22 @@ running.
 
 ## 5.0 Revision History
 
-  - **1.0.0-SNAPSHOT:** 10 August, 2014 - Added "Simple" machine
+  - **1.2.1:** 8 January, 2016 - Remove dependency on Java 8. Now
+    supports compiling and running under Java 1.7.
+
+  - **1.2.0:** 3 January, 2016 - Add symbolic disassembly to breakpoints
+    window.
+  
+  - **1.1.1:** 2 January, 2016 - Minor enhancement: Allows breakpoints
+    to be added with the Enter key.
+
+  - **1.1.0:** 31 December, 2015 - Fixed delay loop to better 
+    simulate various clock speeds. Added ability to select clock
+    speed at runtime. Status display now shows the next instruction
+    to be executed, instead of the last instruction executed.
+    Added support for breakpoints.
+
+  - **1.0.0:** 10 August, 2014 - Added "Simple" machine
     implementation, pure RAM with no IO. Added Klaus Dormann's
     6502 Functional Tests for further machine verification (these
     tests must be run in the "Simple" machine).
@@ -261,7 +292,15 @@ running.
 
   - **0.1:** 20 January, 2010
 
-## 6.0 To Do
+## 6.0 Roadmap
+
+  - **1.2:** Better breakpoint support. Symbolic debugging of breakpoints.
+
+  - **2.0:** Complete rewrite of the UI in JavaFX instead of Swing. Complete
+    assembler and disassembler built in. Ability to attach source code for
+    symbolic debugging.
+
+## 7.0 To Do
 
   - Feedback (in the form of dialogs, status bar, etc).
 
@@ -279,9 +318,13 @@ running.
   - Allow displaying ACIA status and dumping ACIA buffers, for
     debugging.
 
+  - CRTC emulation is very naive. The whole frame is drawn in one
+    CPU step. This should be improved by drawing scan lines during
+    machine steps to approximate real NTSC/PAL refresh rates.
+
   - Symbolic debugging.
 
-## 7.0 Copyright and Acknowledgements
+## 8.0 Copyright and Acknowledgements
 
 **Copyright (c) 2014 Seth J. Morabito <web@loomcom.com>**
 
@@ -301,7 +344,7 @@ This project would not have been possible without the following resources:
   - [Neil Parker's "The 6502/65C02/65C816 Instruction Set Decoded"] (http://www.llx.com/~nparker/a2/opcodes.html),
     for information about how instructions are coded
 
-## 8.0 Licensing
+## 9.0 Licensing
 
 Symon is free software.  It is distributed under the MIT License.
 Please see the file 'COPYING' for full details of the license.

pom.xml

@@ -4,7 +4,7 @@
     <groupId>com.loomcom.symon</groupId>
     <artifactId>symon</artifactId>
     <packaging>jar</packaging>
-    <version>1.0.0</version>
+    <version>1.3.0-SNAPSHOT</version>
     <name>symon</name>
     <url>http://www.loomcom.com/symon</url>
     <properties>
@@ -35,6 +35,11 @@
         </repository>
     </repositories>
     <dependencies>
+        <dependency>
+            <groupId>ch.qos.logback</groupId>
+            <artifactId>logback-classic</artifactId>
+            <version>1.1.3</version>
+        </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
@@ -56,31 +61,10 @@
 
     <build>
         <plugins>
-            <plugin>
-                <artifactId>maven-resources-plugin</artifactId>
-                <version>2.6</version>
-                <executions>
-                    <execution>
-                        <id>copy-resources</id>
-                        <phase>process-resources</phase>
-                        <goals>
-                            <goal>copy-resources</goal>
-                        </goals>
-                        <configuration>
-                            <outputDirectory>${basedir}/target/classes/com/loomcom/symon/ui/images</outputDirectory>
-                            <resources>
-                                <resource>
-                                    <directory>src/main/java/com/loomcom/symon/ui/images</directory>
-                                </resource>
-                            </resources>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-assembly-plugin</artifactId>
-                <version>2.4</version>
+                <version>2.6</version>
                 <configuration>
                     <descriptorRefs>
                         <descriptorRef>jar-with-dependencies</descriptorRef>
@@ -107,8 +91,8 @@
                 <version>3.1</version>
                 <configuration>
                     <compilerArgument>-Xlint:unchecked</compilerArgument>
-                    <source>1.6</source>
+                    <source>1.7</source>
-                    <target>1.6</target>
+                    <target>1.7</target>
                 </configuration>
             </plugin>
 
@@ -116,7 +100,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-jar-plugin</artifactId>
-                <version>2.4</version>
+                <version>2.6</version>
                 <configuration>
                     <archive>
                         <manifest>

samples/echo_irq/Makefile

@@ -7,7 +7,7 @@ echo_irq: echo_irq.o
 	$(LD) -C symon.config -vm -m echo_irq.map -o echo_irq.rom echo_irq.o
 
 echo_irq.o:
-	$(CA) --listing -o echo_irq.o echo_irq.asm
+	$(CA) --listing echo_irq.lst -o echo_irq.o echo_irq.asm
 
 clean:
 	rm -f *.o *.rom *.map *.lst

samples/echo_irq/symon.config

@@ -1,5 +1,5 @@
 MEMORY {
-RAM1: start = $0000, size = $8000;
+RAM1: start = $0000, size = $8000 - __STACKSIZE__;
 ROM1: start = $C000, size = $3FFA, fill = yes;
 ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
 }
@@ -11,6 +11,6 @@ VECTORS:  load = ROMV, type = ro;
 }
 
 SYMBOLS {
-__STACKSIZE__ = $0300;
+__STACKSIZE__: type = weak, value = $0300;
 }
 

samples/ehbasic/Makefile

@@ -7,7 +7,7 @@ ehbasic: ehbasic.o
 	$(LD) -C symon.config -vm -m ehbasic.map -o ehbasic.rom ehbasic.o
 
 ehbasic.o:
-	$(CA) --listing -o ehbasic.o min_mon.asm
+	$(CA) --listing ehbasic.lst -o ehbasic.o min_mon.asm
 
 clean:
 	rm -f *.o *.rom *.map *.lst

samples/ehbasic/min_mon.asm

@@ -150,7 +150,7 @@ END_CODE
 ; sign on string
 
 LAB_mess
-	.byte	$0D,$0A,"Symon (c) 2008-2013, Seth Morabito"
+	.byte	$0D,$0A,"Symon (c) 2008-2014, Seth Morabito"
 	.byte   $0D,$0A,"Enhanced 6502 BASIC 2.22 (c) Lee Davison"
 	.byte   $0D,$0A,"[C]old/[W]arm ?",$00
 

samples/ehbasic/symon.config

@@ -1,5 +1,5 @@
 MEMORY {
-RAM1: start = $0000, size = $8000;
+RAM1: start = $0000, size = $8000 - __STACKSIZE__;
 ROM1: start = $C000, size = $3F00, fill = yes;
 MONITOR: start = $FF00, size = $FA, fill = yes;
 ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
@@ -13,6 +13,6 @@ VECTORS:  load = ROMV, type = ro;
 }
 
 SYMBOLS {
-__STACKSIZE__ = $0300;
+__STACKSIZE__: type = weak, value = $0300;
 }
 

samples/ehbasic_crtc/.gitignore

@@ -0,0 +1,4 @@
+*.rom
+*.lst
+*.map
+*.o

samples/ehbasic_crtc/Makefile

@@ -0,0 +1,13 @@
+CA=ca65
+LD=ld65
+
+all: ehbasic
+
+ehbasic: ehbasic.o
+	$(LD) -C symon.config -vm -m ehbasic.map -o ehbasic.rom ehbasic.o
+
+ehbasic.o:
+	$(CA) --listing ehbasic.lst -o ehbasic.o min_mon.asm
+
+clean:
+	rm -f *.o *.rom *.map *.lst

samples/ehbasic_crtc/README.txt

@@ -0,0 +1,85 @@
+This directoy contains a very slightly modified version of EhBASIC 2.22
+to support the Symon simulator.
+
+Usage
+-----
+
+The pre-assemled ROM image 'ehbasic.rom' in the "samples" directory is all you
+need unless you want to rebuild this source code.
+
+Just copy the image 'ehbasic.rom' to the directory where you run Symon, and
+rename the file to 'rom.bin'. It will be loaded at memory location $D000 when
+the simulator starts up. Click "Run" and you'll be presented with BASIC.
+
+At the first prompt, type 'C' for a Cold Start
+
+When prompted for free memory, type: $C000
+
+Note that EhBASIC only accepts upper case input, so you'll need to use caps
+lock (the cruise control for cool) to really make the most of it.
+
+
+Building
+--------
+
+
+To build it, you'll need the CC65 tool chain from http://www.cc65.org/
+and a suitable version of 'make'. Just typing:
+
+   % make
+   
+in this directory should re-build everything. You'll get a listing,
+some object files, and the ROM image itself.
+
+
+Changes from the EhBASIC 2.22
+-----------------------------
+
+  - Minor syntax changes to allow assembly with the cc65 tool chain.
+
+  - Memory map modified for Symon.
+
+  - At reset, configure the 6551 ACIA for 8-N-1, 2400 baud.
+ 
+  - Monitor routines 'ACIAin' and 'ACIAout' modified for the 6551 ACIA.
+    Specifically, reading and writing will check the 6551 status register for
+    the status of rx and tx registers before receive or transmit.
+
+EhBASIC is copyright Lee Davison <leeedavison@googlemail.com>
+
+My changes are so slight that I hesitate to even say this, but for "CYA"
+reasons:
+
+Changes are copyright Seth Morabito <web@loomcom.com> and are distributed under
+the same license as EhBASIC. I claim no commercial interest whatsoever. Any
+commercial use must be negotiated directly with Lee Davison.
+
+
+Original EhBASIC 2.22 README
+----------------------------
+
+ Enhanced BASIC is a BASIC interpreter for the 6502 family microprocessors. It
+ is constructed to be quick and powerful and easily ported between 6502 systems.
+ It requires few resources to run and includes instructions to facilitate easy
+ low level handling of hardware devices. It also retains most of the powerful
+ high level instructions from similar BASICs.
+
+ EhBASIC is free but not copyright free. For non commercial use there is only one
+ restriction, any derivative work should include, in any binary image distributed,
+ the string "Derived from EhBASIC" and in any distribution that includes human
+ readable files a file that includes the above string in a human readable form
+ e.g. not as a comment in an HTML file.
+
+ For commercial use please contact me,  Lee Davison, at leeedavison@googlemail.com
+ for conditions.
+
+ For more information on EhBASIC, other versions of EhBASIC and other projects
+ please visit my site at ..
+
+	 http://mycorner.no-ip.org/index.html
+
+
+ P.S. c't magazin, henceforth refered to as "those thieving german bastards", are
+ prohibited from using this or any version of EhBASIC for any of their projects
+ or products. The excuse "we don't charge people for it" doesn't wash, it adds
+ value to your product so you owe me.

samples/ehbasic_crtc/min_mon.asm

@@ -0,0 +1,449 @@
+
+; minimal monitor for EhBASIC and 6502 simulator V1.05
+
+; To run EhBASIC on the simulator load and assemble [F7] this file, start the simulator
+; running [F6] then start the code with the RESET [CTRL][SHIFT]R. Just selecting RUN
+; will do nothing, you'll still have to do a reset to run the code.
+
+	.feature labels_without_colons
+	.include "basic.asm"
+
+; put the IRQ and MNI code in RAM so that it can be changed
+
+IRQ_vec	= VEC_SV+2		; IRQ code vector
+NMI_vec	= IRQ_vec+$0A	; NMI code vector
+
+; setup for the 6502 simulator environment
+
+IO_AREA		= $8800
+ACIAdata	= IO_AREA	; simulated ACIA r/w port
+ACIAstatus	= IO_AREA+1
+ACIAcommand	= IO_AREA+2
+ACIAcontrol	= IO_AREA+3
+
+	CRTC_A	= $9000		; CRTC register select
+	CRTC_C	= $9001		; CRTC register IO
+	CADDR_L	= $E0		; Cursor address (low)
+	CADDR_H	= $E1		; Cursor address (high)
+	C_COL	= $E2		; Cursor column
+	C_ROW	= $E3		; Cursor row
+	COUTC	= $E4		; Temp storage for char out.
+	R_STRT	= $E5		; E5,E6 contains starting address of
+				; current row
+	R_NXT	= $E7		; E7,E8 contains starting address of
+				; next row
+
+	N_ROWS	= 24
+	N_COLS	= 40
+
+
+; now the code. all this does is set up the vectors and interrupt code
+; and wait for the user to select [C]old or [W]arm start. nothing else
+; fits in less than 128 bytes
+
+.segment "MONITOR"
+	.org	$FC00		; pretend this is in a 1/8K ROM
+
+; reset vector points here
+
+RES_vec:
+	CLD			; clear decimal mode
+	LDX	#$FF		; empty stack
+	TXS			; set the stack
+
+	;; Initialize the CRTC
+	LDA	#$01
+	STA	CRTC_A
+	LDA	#N_COLS		; 40 columns
+	STA	CRTC_C
+	LDA	#$06
+	STA	CRTC_A
+	LDA	#N_ROWS		; 24 rows
+	STA	CRTC_C
+	LDA	#$70
+	STA	CADDR_H
+	LDA	#$00
+	STA	CADDR_L
+	STA	C_ROW
+	STA	C_COL
+	JSR	CLRVID
+	;; TODO: Initialize params on CRTC
+
+; Initialize the ACIA
+ACIA_init:
+	LDA	#$00
+	STA	ACIAstatus		; Soft reset
+	LDA	#$0B
+	STA	ACIAcommand		; Parity disabled, IRQ disabled
+	LDA	#$1E
+	STA	ACIAcontrol		; Set output for 8-N-1 9600
+
+; set up vectors and interrupt code, copy them to page 2
+
+	LDY	#END_CODE-LAB_vec	; set index/count
+LAB_stlp:
+	LDA	LAB_vec-1,Y		; get byte from interrupt code
+	STA	VEC_IN-1,Y		; save to RAM
+	DEY				; decrement index/count
+	BNE	LAB_stlp		; loop if more to do
+
+; now do the signon message, Y = $00 here
+
+LAB_signon:
+	LDA	LAB_mess,Y	; get byte from sign on message
+	BEQ	LAB_nokey	; exit loop if done
+
+	JSR	V_OUTP		; output character
+	INY			; increment index
+	BNE	LAB_signon	; loop, branch always
+
+LAB_nokey:
+	JSR	V_INPT		; call scan input device
+	BCC	LAB_nokey	; loop if no key
+
+	AND	#$DF		; mask xx0x xxxx, ensure upper case
+	CMP	#'W'		; compare with [W]arm start
+	BEQ	LAB_dowarm	; branch if [W]arm start
+
+	CMP	#'C'		; compare with [C]old start
+	BNE	RES_vec		; loop if not [C]old start
+
+	JMP	LAB_COLD	; do EhBASIC cold start
+
+LAB_dowarm:
+	JMP	LAB_WARM	; do EhBASIC warm start
+
+
+ACIAout:
+
+	PHA
+@loop:	LDA	ACIAstatus
+	AND	#$10
+	BEQ	@loop		; Wait for buffer to empty
+	PLA
+	STA	ACIAdata
+	RTS
+
+;;; Byte out to the CRTC
+;;;
+;;; 1. Increment cursor position.
+;;; 2. Scroll if necessary.
+;;; 3. Store new cursor position in CRTC.
+
+CRTCout:
+	JSR	ACIAout		; Also echo to terminal for debugging.
+
+	;; In parallel, we're maintaining two states:
+	;;    - The address of the cursor, and
+	;;    - The Column/Row of the cursor.
+	;;
+	;; The latter state is used to handle scrolling and
+	;; for knowing how far to back up the cursor
+	;; for a carriage-return.
+
+	;; Backspace
+	CMP	#$08
+	BEQ	DO_BS
+	;; Line Feed
+	CMP	#$0a
+	BEQ	DO_LF
+	;; Carriage Return
+	CMP	#$0d
+	BEQ	DO_CR
+	;; Any other character...
+	STA	COUTC		; Store the character going out
+	JSR	COUT1		; Output it where the cursor is.
+	;; We might need to scroll...
+	LDA	C_ROW
+	CMP	#N_ROWS-1
+	BNE	@noscr
+	LDA	C_COL
+	CMP	#N_COLS-1
+	BNE	@noscr
+	;; ... yup, we DO need to scroll.
+	JSR	DO_SCROLL
+	RTS
+@noscr:	JSR	INC_CADDR
+	INC	C_COL
+	JSR	SET_CURSOR
+	RTS
+
+	;; Handle a back-space character.
+DO_BS:	LDA	C_COL
+	BNE	@l1		; Skip next bit
+	LDA	#N_COLS-1
+	STA	C_COL
+	BNE	@l2
+@l1:	DEC	C_COL
+@l2:	JSR	DEC_CADDR	; Back up
+	JSR	SET_CURSOR
+
+@l3:	LDA	#$20
+	STA	COUTC		; Echo a space ($20)
+	JSR	COUT1
+	RTS
+
+DO_LF:	RTS			; Just swallow LF. CR emulates it.
+
+DO_CR:	SEC
+	LDA	CADDR_L		; 1. Carriage return to start of row.
+	SBC	C_COL
+	STA	CADDR_L
+	LDA	CADDR_H
+	SBC	#$00		; Will decrement H if carry was left
+				; set.
+	STA	CADDR_H
+
+	;; 1. Are we on the last row? Scroll.
+	LDA	C_ROW
+	CMP	#N_ROWS-1
+	BNE	@inc
+	JSR	DO_SCROLL
+	RTS
+
+@inc:	JSR	INCROW
+
+@lf:	CLC
+	LDA	CADDR_L
+	ADC	#$28		; Now add $28
+	STA	CADDR_L
+	LDA	CADDR_H
+	ADC	#$00		; Will increment if carry was set
+	STA	CADDR_H
+
+	LDA	#$00		; Reset cursor row to 0
+	STA	C_COL
+	JSR	SET_CURSOR
+	RTS
+
+SET_CURSOR:
+	LDA	#14
+	STA	CRTC_A
+	LDA	CADDR_H
+	STA	CRTC_C
+	LDA	#15
+	STA	CRTC_A
+	LDA	CADDR_L
+	STA	CRTC_C
+	RTS
+
+	;; Increment C_ROW and put new
+	;; line start address in R_STRT,R_STRT+1
+INCROW:	TYA
+	PHA
+	INC	C_ROW
+	BNE	DECR2	      ; Share code with DECROW
+
+	;; Decrement C_ROW and put new
+	;; line start address in R_STRT,R_STRT+1
+DECROW:	TYA
+	PHA
+	DEC	C_ROW
+DECR2:	JSR	SETRSTRT
+	PLA
+	TAY
+	RTS
+
+	;; Send the cursor home to the start of the line
+HOME:
+	LDY	C_ROW
+	LDA	CRA_LO,Y
+	STA	CADDR_L
+	LDA	CRA_HI,Y
+	STA	CADDR_H
+	LDA	#$00
+	STA	C_COL
+	RTS
+
+	;; Set the start address of the current row
+SETRSTRT:
+	LDY	C_ROW
+	LDA	CRA_LO,Y
+	STA	R_STRT
+	LDA	CRA_HI,Y
+	STA	R_STRT+1
+	RTS
+
+	;; Clear the current video line
+CLRLN:	LDA	#$20
+	LDY	#$00
+@l1:	STA	(R_STRT),Y
+	INY
+	CPY	#N_COLS
+	BNE	@l1
+	RTS
+
+	;; Clear the video window and put the cursor at the home
+	;; position
+CLRVID:
+	LDA	#$20
+	LDX	#N_ROWS-1
+@l1:	STX	C_ROW
+	JSR	SETRSTRT
+	JSR	CLRLN
+	DEX
+	BPL	@l1
+	RTS
+
+	;; Handle a scroll request.
+	;;
+	;; The cursor could be anywhere on the line when this scroll
+	;; request comes in.
+DO_SCROLL:
+	PHA
+	TYA
+	PHA
+	TXA
+	PHA
+
+	;; The idea here is to copy each line to the line above it
+	LDX	#$00
+
+@l1:	LDA	CRA_LO,X
+	STA	R_STRT
+	LDA	CRA_HI,X
+	STA	R_STRT+1
+
+	INX
+
+	LDA	CRA_LO,X
+	STA	R_NXT
+	LDA	CRA_HI,X
+	STA	R_NXT+1
+
+	LDY	#0
+@l2:	LDA	(R_NXT),Y
+	STA	(R_STRT),Y
+	INY
+	CPY	#N_COLS
+	BNE	@l2
+
+	CPX	#N_ROWS
+	BNE	@l1
+
+	;; Clear the line the cursor occupies.
+	JSR	CLRLN
+
+	;; Move the cursor to the beginning of the line
+	JSR	HOME
+	JSR	SET_CURSOR
+
+	PLA
+	TAX
+	PLA
+	TAY			; Restore Y
+	PLA
+	RTS
+
+	;; Decrement the cursor address
+INC_CADDR:
+	INC	CADDR_L
+	BNE	@l1		; Did we increment to 0?
+	INC	CADDR_H		; Yes, also increment high
+@l1:	RTS
+
+	;; Increment the cursor address
+DEC_CADDR:
+	CMP	CADDR_L		; Is low alrady 0?
+	BNE	@l1
+	DEC	CADDR_H		; Yes, decrement high
+@l1:	DEC	CADDR_L
+	RTS
+
+COUT1:
+	TYA
+	PHA			; Save Y
+	LDY	#$00
+	LDA	COUTC
+	STA	(CADDR_L),Y
+	PLA
+	TAY			; Restore Y
+	RTS
+
+;;;
+;;; byte in from ACIA. This subroutine will also force
+;;; all lowercase letters to be uppercase, because EhBASIC
+;;; only understands upper-case tokens
+;;;
+ACIAin:
+	LDA	ACIAstatus	; Read 6551 status
+	AND	#$08		;
+	BEQ	LAB_nobyw	; If rx buffer empty, no byte
+
+	LDA	ACIAdata	; Read byte from 6551
+	CMP	#'a'		; Is it < 'a'?
+	BCC	@done		; Yes, we're done
+	CMP	#'{'		; Is it >= '{'?
+	BCS	@done		; Yes, we're done
+	AND	#$5f		; Otherwise, mask to uppercase
+@done:
+	SEC			; Flag byte received
+	RTS
+
+LAB_nobyw:
+	CLC			; flag no byte received
+no_load:			; empty load vector for EhBASIC
+no_save:			; empty save vector for EhBASIC
+	RTS
+
+; vector tables
+
+LAB_vec:
+	.word	ACIAin		; byte in from simulated ACIA
+	.word	CRTCout		; byte out to simulated ACIA
+	.word	no_load		; null load vector for EhBASIC
+	.word	no_save		; null save vector for EhBASIC
+
+; EhBASIC IRQ support
+
+IRQ_CODE:
+	PHA			; save A
+	LDA	IrqBase		; get the IRQ flag byte
+	LSR			; shift the set b7 to b6, and on down ...
+	ORA	IrqBase		; OR the original back in
+	STA	IrqBase		; save the new IRQ flag byte
+	PLA			; restore A
+	RTI
+
+; EhBASIC NMI support
+
+NMI_CODE:
+	PHA			; save A
+	LDA	NmiBase		; get the NMI flag byte
+	LSR			; shift the set b7 to b6, and on down ...
+	ORA	NmiBase		; OR the original back in
+	STA	NmiBase		; save the new NMI flag byte
+	PLA			; restore A
+	RTI
+
+END_CODE:
+
+
+;;; CRTC row addresses: HIGH
+CRA_HI:
+	.byte	$70,$70,$70,$70,$70,$70,$70,$71
+	.byte	$71,$71,$71,$71,$71,$72,$72,$72
+	.byte	$72,$72,$72,$72,$73,$73,$73,$73
+
+
+;;; CRTC row addresses: LOW
+CRA_LO:
+	.byte	$00,$28,$50,$78,$A0,$C8,$F0,$18
+	.byte	$40,$68,$90,$B8,$E0,$08,$30,$58
+	.byte	$80,$A8,$D0,$F8,$20,$48,$70,$98
+
+; sign on string
+LAB_mess:
+	.byte	$0D,$0A,"SYMON (C) 2008-2014, SETH MORABITO"
+	.byte   $0D,$0A,"ENHANCED 6502 BASIC 2.22 (C) LEE DAVISON"
+	.byte   $0D,$0A,"[C]OLD/[W]ARM ?",$00
+
+
+; system vectors
+
+.segment "VECTORS"
+	.org	$FFFA
+
+	.word	NMI_vec		; NMI vector
+	.word	RES_vec		; RESET vector
+	.word	IRQ_vec		; IRQ vector

samples/ehbasic_crtc/symon.config

@@ -0,0 +1,18 @@
+MEMORY {
+RAM1: start = $0000, size = $8000 - __STACKSIZE__;
+ROM1: start = $C000, size = $3C00, fill = yes;
+MONITOR: start = $FC00, size = $3FA, fill = yes;
+ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
+}
+
+SEGMENTS {
+CODE:     load = ROM1, type = ro;
+DATA:     load = ROM1, type = ro;
+MONITOR:  load = MONITOR, type = ro;
+VECTORS:  load = ROMV, type = ro;
+}
+
+SYMBOLS {
+__STACKSIZE__: type = weak, value = $0300;
+}
+

src/main/java/com/loomcom/symon/Breakpoints.java

@@ -0,0 +1,85 @@
+package com.loomcom.symon;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.util.Utils;
+
+import javax.swing.table.AbstractTableModel;
+import java.util.ArrayList;
+import java.util.TreeSet;
+
+public class Breakpoints extends AbstractTableModel {
+
+    private TreeSet<Integer> breakpoints;
+    private Simulator simulator;
+
+    public Breakpoints(Simulator simulator) {
+        this.breakpoints = new TreeSet<>();
+        this.simulator = simulator;
+    }
+
+    public boolean contains(int address) {
+        return this.breakpoints.contains(address);
+    }
+
+    public void addBreakpoint(int address) {
+        this.breakpoints .add(address);
+        fireTableDataChanged();
+    }
+
+    public void removeBreakpoint(int address) {
+        this.breakpoints.remove(address);
+        fireTableDataChanged();
+    }
+
+    public void removeBreakpointAtIndex(int index) {
+        if (index < 0) {
+            return;
+        }
+
+        ArrayList<Integer> values = new ArrayList<>(breakpoints);
+        int value = values.get(index);
+        this.breakpoints.remove(value);
+        fireTableDataChanged();
+    }
+
+    public void refresh() {
+        fireTableDataChanged();
+    }
+
+    @Override
+    public String getColumnName(int index) {
+        if (index == 0) {
+            return "Address";
+        } else {
+            return "Inst";
+        }
+    }
+
+    @Override
+    public int getRowCount() {
+        return breakpoints.size();
+    }
+
+    @Override
+    public int getColumnCount() {
+        return 2;
+    }
+
+    @Override
+    public Object getValueAt(int rowIndex, int columnIndex) {
+        ArrayList<Integer> values = new ArrayList<>(breakpoints);
+
+        if (columnIndex == 0) {
+            return "$" + Utils.wordToHex(values.get(rowIndex));
+        } else if (columnIndex == 1) {
+            int address = values.get(rowIndex);
+            try {
+                return simulator.disassembleOpAtAddress(address);
+            } catch (MemoryAccessException ex) {
+                return "???";
+            }
+        } else {
+            return null;
+        }
+    }
+}

src/main/java/com/loomcom/symon/Bus.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -26,6 +26,7 @@ package com.loomcom.symon;
 import com.loomcom.symon.devices.Device;
 import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
+
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -62,7 +63,7 @@ public class Bus {
     }
 
     public Bus(int startAddress, int endAddress) {
-        this.deviceMap = new HashMap<Integer, SortedSet<Device>>();
+        this.deviceMap = new HashMap<>();
         this.startAddress = startAddress;
         this.endAddress = endAddress;
     }
@@ -92,24 +93,26 @@ public class Bus {
     /**
      * Add a device to the bus.
      *
-     * @param device
+     * @param device   Device to add
-     * @param priority
+     * @param priority Bus prioirity.
      * @throws MemoryRangeException
      */
     public void addDevice(Device device, int priority) throws MemoryRangeException {
 
         MemoryRange range = device.getMemoryRange();
+
         if (range.startAddress() < this.startAddress || range.startAddress() > this.endAddress) {
             throw new MemoryRangeException("start address of device " + device.getName() + " does not fall within the address range of the bus");
         }
+
         if (range.endAddress() < this.startAddress || range.endAddress() > this.endAddress) {
             throw new MemoryRangeException("end address of device " + device.getName() + " does not fall within the address range of the bus");
         }
 
-        
         SortedSet<Device> deviceSet = deviceMap.get(priority);
+
         if (deviceSet == null) {
-            deviceSet = new TreeSet<Device>();
+            deviceSet = new TreeSet<>();
             deviceMap.put(priority, deviceSet);
         }
 
@@ -121,7 +124,7 @@ public class Bus {
     /**
      * Add a device to the bus. Throws a MemoryRangeException if the device overlaps with any others.
      *
-     * @param device
+     * @param device Device to add
      * @throws MemoryRangeException
      */
     public void addDevice(Device device) throws MemoryRangeException {
@@ -132,7 +135,7 @@ public class Bus {
     /**
      * Remove a device from the bus.
      *
-     * @param device
+     * @param device Device to remove
      */
     public void removeDevice(Device device) {
         for (SortedSet<Device> deviceSet : deviceMap.values()) {
@@ -170,7 +173,7 @@ public class Bus {
         if (d != null) {
             MemoryRange range = d.getMemoryRange();
             int devAddr = address - range.startAddress();
-            return d.read(devAddr);
+            return d.read(devAddr) & 0xff;
         }
 
         throw new MemoryAccessException("Bus read failed. No device at address " + String.format("$%04X", address));
@@ -214,9 +217,9 @@ public class Bus {
 
     public SortedSet<Device> getDevices() {
         // create an ordered set of devices, ordered by device priorities
-        SortedSet<Device> devices = new TreeSet<Device>();
+        SortedSet<Device> devices = new TreeSet<>();
 
-        List<Integer> priorities = new ArrayList<Integer>(deviceMap.keySet());
+        List<Integer> priorities = new ArrayList<>(deviceMap.keySet());
         Collections.sort(priorities);
 
         for (int priority : priorities) {

src/main/java/com/loomcom/symon/Cpu.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2012 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -24,9 +24,10 @@
 package com.loomcom.symon;
 
 import com.loomcom.symon.exceptions.MemoryAccessException;
-import com.loomcom.symon.util.HexUtil;
+import com.loomcom.symon.util.Utils;
-import java.util.logging.Level;
+import org.slf4j.Logger;
-import java.util.logging.Logger;
+import org.slf4j.LoggerFactory;
+
 
 /**
  * This class provides a simulation of the MOS 6502 CPU's state machine.
@@ -35,6 +36,8 @@ import java.util.logging.Logger;
  */
 public class Cpu implements InstructionTable {
 
+    private final static Logger logger = LoggerFactory.getLogger(Cpu.class.getName());
+
     /* Process status register mnemonics */
     public static final int P_CARRY       = 0x01;
     public static final int P_ZERO        = 0x02;
@@ -55,24 +58,19 @@ public class Cpu implements InstructionTable {
     public static final int IRQ_VECTOR_L = 0xfffe;
     public static final int IRQ_VECTOR_H = 0xffff;
 
+    public static final long DEFAULT_CLOCK_PERIOD_IN_NS = 1000;
+
+    /* Simulated clock speed (default is 1MHz) */
+    private long clockPeriodInNs = DEFAULT_CLOCK_PERIOD_IN_NS;
+
     /* Simulated behavior */
-    private static CpuBehavior behavior;
+    private CpuBehavior behavior;
 
     /* The Bus */
     private Bus bus;
 
     /* The CPU state */
-    private static final CpuState state = new CpuState();
+    private final CpuState state = new CpuState();
-
-    /* Scratch space for addressing mode and effective address
-     * calculations */
-    private int irAddressMode; // Bits 3-5 of IR:  [ | | |X|X|X| | ]
-    private int irOpMode;      // Bits 6-7 of IR:  [ | | | | | |X|X]
-    private int effectiveAddress;
-
-    /* Internal scratch space */
-    private int lo = 0, hi = 0;  // Used in address calculation
-    private int tmp; // Temporary storage
 
     /* start time of op execution, needed for speed simulation */
     private long opBeginTime;
@@ -81,7 +79,7 @@ public class Cpu implements InstructionTable {
      * Construct a new CPU.
      */
     public Cpu() {
-        this(CpuBehavior.NMOS_WITH_INDIRECT_JMP_BUG);
+        this(CpuBehavior.NMOS_6502);
     }
 
     public Cpu(CpuBehavior behavior) {
@@ -106,10 +104,6 @@ public class Cpu implements InstructionTable {
         this.behavior = behavior;
     }
 
-    public CpuBehavior getBehavior() {
-        return behavior;
-    }
-
     /**
      * Reset the CPU to known initial values.
      */
@@ -120,7 +114,7 @@ public class Cpu implements InstructionTable {
         state.sp = 0xff;
 
         // Set the PC to the address stored in the reset vector
-        state.pc = address(bus.read(RST_VECTOR_L), bus.read(RST_VECTOR_H));
+        state.pc = Utils.address(bus.read(RST_VECTOR_L), bus.read(RST_VECTOR_H));
 
         // Clear instruction register.
         state.ir = 0;
@@ -146,6 +140,8 @@ public class Cpu implements InstructionTable {
         state.a = 0;
         state.x = 0;
         state.y = 0;
+
+        peekAhead();
     }
 
     public void step(int num) throws MemoryAccessException {
@@ -159,6 +155,7 @@ public class Cpu implements InstructionTable {
      */
     public void step() throws MemoryAccessException {
         opBeginTime = System.nanoTime();
+
         // Store the address from which the IR was read, for debugging
         state.lastPc = state.pc;
 
@@ -172,8 +169,8 @@ public class Cpu implements InstructionTable {
 
         // Fetch memory location for this instruction.
         state.ir = bus.read(state.pc);
-        irAddressMode = (state.ir >> 2) & 0x07;
+        int irAddressMode = (state.ir >> 2) & 0x07;  // Bits 3-5 of IR:  [ | | |X|X|X| | ]
-        irOpMode = state.ir & 0x03;
+        int irOpMode = state.ir & 0x03;              // Bits 6-7 of IR:  [ | | | | | |X|X]
 
         incrementPC();
 
@@ -190,7 +187,8 @@ public class Cpu implements InstructionTable {
         state.stepCounter++;
 
         // Get the data from the effective address (if any)
-        effectiveAddress = 0;
+        int effectiveAddress = 0;
+        int tmp; // Temporary storage
 
         switch (irOpMode) {
             case 0:
@@ -204,7 +202,14 @@ public class Cpu implements InstructionTable {
                     case 2: // Accumulator - ignored
                         break;
                     case 3: // Absolute
-                        effectiveAddress = address(state.args[0], state.args[1]);
+                        effectiveAddress = Utils.address(state.args[0], state.args[1]);
+                        break;
+                    case 4: // 65C02 (Zero Page)
+                        if (behavior == CpuBehavior.CMOS_6502 ||
+                            behavior == CpuBehavior.CMOS_65816) {
+                            effectiveAddress = Utils.address(bus.read(state.args[0]),
+                                                             bus.read((state.args[0] + 1) & 0xff));
+                        }
                         break;
                     case 5: // Zero Page,X / Zero Page,Y
                         if (state.ir == 0x96 || state.ir == 0xb6) {
@@ -226,7 +231,7 @@ public class Cpu implements InstructionTable {
                 switch (irAddressMode) {
                     case 0: // (Zero Page,X)
                         tmp = (state.args[0] + state.x) & 0xff;
-                        effectiveAddress = address(bus.read(tmp), bus.read(tmp + 1));
+                        effectiveAddress = Utils.address(bus.read(tmp), bus.read(tmp + 1));
                         break;
                     case 1: // Zero Page
                         effectiveAddress = state.args[0];
@@ -235,10 +240,10 @@ public class Cpu implements InstructionTable {
                         effectiveAddress = -1;
                         break;
                     case 3: // Absolute
-                        effectiveAddress = address(state.args[0], state.args[1]);
+                        effectiveAddress = Utils.address(state.args[0], state.args[1]);
                         break;
                     case 4: // (Zero Page),Y
-                        tmp = address(bus.read(state.args[0]),
+                        tmp = Utils.address(bus.read(state.args[0]),
                                       bus.read((state.args[0] + 1) & 0xff));
                         effectiveAddress = (tmp + state.y) & 0xffff;
                         break;
@@ -260,9 +265,7 @@ public class Cpu implements InstructionTable {
 
             /** Single Byte Instructions; Implied and Relative **/
             case 0x00: // BRK - Force Interrupt - Implied
-                if (!getIrqDisableFlag()) {
+                handleBrk(state.pc + 1);
-                    handleIrq(state.pc + 1);
-                }
                 break;
             case 0x08: // PHP - Push Processor Status - Implied
                 // Break flag is always set in the stack value.
@@ -279,7 +282,7 @@ public class Cpu implements InstructionTable {
             case 0x20: // JSR - Jump to Subroutine - Implied
                 stackPush((state.pc - 1 >> 8) & 0xff); // PC high byte
                 stackPush(state.pc - 1 & 0xff);        // PC low byte
-                state.pc = address(state.args[0], state.args[1]);
+                state.pc = Utils.address(state.args[0], state.args[1]);
                 break;
             case 0x28: // PLP - Pull Processor Status - Implied
                 setProcessorStatus(stackPop());
@@ -294,9 +297,9 @@ public class Cpu implements InstructionTable {
                 break;
             case 0x40: // RTI - Return from Interrupt - Implied
                 setProcessorStatus(stackPop());
-                lo = stackPop();
+                int lo = stackPop();
-                hi = stackPop();
+                int hi = stackPop();
-                setProgramCounter(address(lo, hi));
+                setProgramCounter(Utils.address(lo, hi));
                 break;
             case 0x48: // PHA - Push Accumulator - Implied
                 stackPush(state.a);
@@ -312,7 +315,7 @@ public class Cpu implements InstructionTable {
             case 0x60: // RTS - Return from Subroutine - Implied
                 lo = stackPop();
                 hi = stackPop();
-                setProgramCounter((address(lo, hi) + 1) & 0xffff);
+                setProgramCounter((Utils.address(lo, hi) + 1) & 0xffff);
                 break;
             case 0x68: // PLA - Pull Accumulator - Implied
                 state.a = stackPop();
@@ -400,20 +403,21 @@ public class Cpu implements InstructionTable {
 
             /** JMP *****************************************************************/
             case 0x4c: // JMP - Absolute
-                state.pc = address(state.args[0], state.args[1]);
+                state.pc = Utils.address(state.args[0], state.args[1]);
                 break;
+            // TODO: 65C02 instruction 0x7C, JMP (Indirect,X)
             case 0x6c: // JMP - Indirect
-                lo = address(state.args[0], state.args[1]); // Address of low byte
+                lo = Utils.address(state.args[0], state.args[1]); // Address of low byte
 
                 if (state.args[0] == 0xff &&
-                    (behavior == CpuBehavior.NMOS_WITH_INDIRECT_JMP_BUG ||
+                    (behavior == CpuBehavior.NMOS_6502 ||
                      behavior == CpuBehavior.NMOS_WITH_ROR_BUG)) {
-                    hi = address(0x00, state.args[1]);
+                    hi = Utils.address(0x00, state.args[1]);
                 } else {
                     hi = lo + 1;
                 }
 
-                state.pc = address(bus.read(lo), bus.read(hi));
+                state.pc = Utils.address(bus.read(lo), bus.read(hi));
                 /* TODO: For accuracy, allow a flag to enable broken behavior of early 6502s:
                  *
                  * "An original 6502 has does not correctly fetch the target
@@ -426,13 +430,20 @@ public class Cpu implements InstructionTable {
                  * (http://www.obelisk.demon.co.uk/6502/reference.html#JMP)
                  */
                 break;
-
+            case 0x7C: // 65C02 JMP - Absolute,X
+                state.pc = (Utils.address(state.args[0], state.args[1]) + state.x) & 0xffff;
+                break;
 
             /** ORA - Logical Inclusive Or ******************************************/
             case 0x09: // #Immediate
                 state.a |= state.args[0];
                 setArithmeticFlags(state.a);
                 break;
+            case 0x12: // 65C02 ORA (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0x01: // (Zero Page,X)
             case 0x05: // Zero Page
             case 0x0d: // Absolute
@@ -475,6 +486,11 @@ public class Cpu implements InstructionTable {
                 state.a &= state.args[0];
                 setArithmeticFlags(state.a);
                 break;
+            case 0x32: // 65C02 AND (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0x21: // (Zero Page,X)
             case 0x25: // Zero Page
             case 0x2d: // Absolute
@@ -507,6 +523,11 @@ public class Cpu implements InstructionTable {
                 state.a ^= state.args[0];
                 setArithmeticFlags(state.a);
                 break;
+            case 0x52: // 65C02 EOR (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0x41: // (Zero Page,X)
             case 0x45: // Zero Page
             case 0x4d: // Absolute
@@ -542,6 +563,11 @@ public class Cpu implements InstructionTable {
                     state.a = adc(state.a, state.args[0]);
                 }
                 break;
+            case 0x72: // 65C02 ADC (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0x61: // (Zero Page,X)
             case 0x65: // Zero Page
             case 0x6d: // Absolute
@@ -573,6 +599,11 @@ public class Cpu implements InstructionTable {
 
 
             /** STA - Store Accumulator *********************************************/
+            case 0x92: // 65C02 STA (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0x81: // (Zero Page,X)
             case 0x85: // Zero Page
             case 0x8d: // Absolute
@@ -633,6 +664,11 @@ public class Cpu implements InstructionTable {
                 state.a = state.args[0];
                 setArithmeticFlags(state.a);
                 break;
+            case 0xb2: // 65C02 LDA (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0xa1: // (Zero Page,X)
             case 0xa5: // Zero Page
             case 0xad: // Absolute
@@ -659,6 +695,11 @@ public class Cpu implements InstructionTable {
             case 0xc9: // #Immediate
                 cmp(state.a, state.args[0]);
                 break;
+            case 0xd2: // 65C02 CMP (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0xc1: // (Zero Page,X)
             case 0xc5: // Zero Page
             case 0xcd: // Absolute
@@ -699,6 +740,11 @@ public class Cpu implements InstructionTable {
                     state.a = sbc(state.a, state.args[0]);
                 }
                 break;
+            case 0xf2: // 65C02 SBC (ZP)
+                if (behavior == CpuBehavior.NMOS_6502 ||
+                    behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
+                    break;
+                }
             case 0xe1: // (Zero Page,X)
             case 0xe5: // Zero Page
             case 0xed: // Absolute
@@ -732,15 +778,32 @@ public class Cpu implements InstructionTable {
         }
 
         delayLoop(state.ir);
+
+        // Peek ahead to the next insturction and arguments
+        peekAhead();
+    }
+
+    private void peekAhead() throws MemoryAccessException {
+        state.nextIr = bus.read(state.pc);
+        int nextInstSize = Cpu.instructionSizes[state.nextIr];
+        for (int i = 1; i < nextInstSize; i++) {
+            int nextRead = (state.pc + i) % bus.endAddress();
+            state.nextArgs[i-1] = bus.read(nextRead);
+        }
+    }
+
+    private void handleBrk(int returnPc) throws MemoryAccessException {
+        handleInterrupt(returnPc, IRQ_VECTOR_L, IRQ_VECTOR_H, true);
+        clearIrq();
     }
 
     private void handleIrq(int returnPc) throws MemoryAccessException {
-        handleInterrupt(returnPc, IRQ_VECTOR_L, IRQ_VECTOR_H);
+        handleInterrupt(returnPc, IRQ_VECTOR_L, IRQ_VECTOR_H, false);
         clearIrq();
     }
 
     private void handleNmi() throws MemoryAccessException {
-        handleInterrupt(state.pc, NMI_VECTOR_L, NMI_VECTOR_H);
+        handleInterrupt(state.pc, NMI_VECTOR_L, NMI_VECTOR_H, false);
         clearNmi();
     }
 
@@ -749,9 +812,19 @@ public class Cpu implements InstructionTable {
      *
      * @throws MemoryAccessException
      */
-    private void handleInterrupt(int returnPc, int vectorLow, int vectorHigh) throws MemoryAccessException {
+    private void handleInterrupt(int returnPc, int vectorLow, int vectorHigh, boolean isBreak) throws MemoryAccessException {
+
+        if (isBreak)
+        {
             // Set the break flag before pushing.
             setBreakFlag();
+        }
+        else
+        {
+            // IRQ & NMI clear break flag
+            clearBreakFlag();
+        }
+
         // Push program counter + 1 onto the stack
         stackPush((returnPc >> 8) & 0xff); // PC high byte
         stackPush(returnPc & 0xff);        // PC low byte
@@ -760,7 +833,7 @@ public class Cpu implements InstructionTable {
         setIrqDisableFlag();
 
         // Load interrupt vector address into PC
-        state.pc = address(bus.read(vectorLow), bus.read(vectorHigh));
+        state.pc = Utils.address(bus.read(vectorLow), bus.read(vectorHigh));
     }
 
     /**
@@ -770,7 +843,7 @@ public class Cpu implements InstructionTable {
      *
      * @param acc     The current value of the accumulator
      * @param operand The operand
-     * @return
+     * @return The sum of the accumulator and the operand
      */
     private int adc(int acc, int operand) {
         int result = (operand & 0xff) + (acc & 0xff) + getCarryBit();
@@ -893,6 +966,14 @@ public class Cpu implements InstructionTable {
         return result;
     }
 
+    /**
+     * @param clockPeriodInNs The simulated clock period, in nanoseconds
+     */
+    public void setClockPeriodInNs(long clockPeriodInNs) {
+        logger.debug("Setting simulated clock period to {} ns.", clockPeriodInNs);
+        this.clockPeriodInNs = clockPeriodInNs;
+    }
+
     /**
      * Return the current Cpu State.
      *
@@ -1117,6 +1198,14 @@ public class Cpu implements InstructionTable {
 
     public void setProgramCounter(int addr) {
         state.pc = addr;
+
+        // As a side-effect of setting the program counter,
+        // we want to peek ahead at the next state.
+        try {
+            peekAhead();
+        } catch (MemoryAccessException ex) {
+            logger.error("Could not peek ahead at next instruction state.");
+        }
     }
 
     public int getStackPointer() {
@@ -1172,23 +1261,23 @@ public class Cpu implements InstructionTable {
     }
 
     public String getAccumulatorStatus() {
-        return "$" + HexUtil.byteToHex(state.a);
+        return "$" + Utils.byteToHex(state.a);
     }
 
     public String getXRegisterStatus() {
-        return "$" + HexUtil.byteToHex(state.x);
+        return "$" + Utils.byteToHex(state.x);
     }
 
     public String getYRegisterStatus() {
-        return "$" + HexUtil.byteToHex(state.y);
+        return "$" + Utils.byteToHex(state.y);
     }
 
     public String getProgramCounterStatus() {
-        return "$" + HexUtil.wordToHex(state.pc);
+        return "$" + Utils.wordToHex(state.pc);
     }
 
     public String getStackPointerStatus() {
-        return "$" + HexUtil.byteToHex(state.sp);
+        return "$" + Utils.byteToHex(state.sp);
     }
 
     public int getProcessorStatus() {
@@ -1272,19 +1361,12 @@ public class Cpu implements InstructionTable {
         }
     }
 
-    /**
-     * Given two bytes, return an address.
-     */
-    int address(int lowByte, int hiByte) {
-        return ((hiByte << 8) | lowByte) & 0xffff;
-    }
-
     /**
      * Given a hi byte and a low byte, return the Absolute,X
      * offset address.
      */
     int xAddress(int lowByte, int hiByte) {
-        return (address(lowByte, hiByte) + state.x) & 0xffff;
+        return (Utils.address(lowByte, hiByte) + state.x) & 0xffff;
     }
 
     /**
@@ -1292,7 +1374,7 @@ public class Cpu implements InstructionTable {
      * offset address.
      */
     int yAddress(int lowByte, int hiByte) {
-        return (address(lowByte, hiByte) + state.y) & 0xffff;
+        return (Utils.address(lowByte, hiByte) + state.y) & 0xffff;
     }
 
     /**
@@ -1302,6 +1384,13 @@ public class Cpu implements InstructionTable {
         return (zp + state.x) & 0xff;
     }
 
+    /**
+     * Given a single byte, compute the Zero Page,Y offset address.
+     */
+    int zpyAddress(int zp) {
+        return (zp + state.y) & 0xff;
+    }
+
     /**
      * Given a single byte, compute the offset address.
      */
@@ -1310,187 +1399,40 @@ public class Cpu implements InstructionTable {
         return (state.pc + (byte) offset) & 0xffff;
     }
 
-    /**
-     * Given a single byte, compute the Zero Page,Y offset address.
-     */
-    int zpyAddress(int zp) {
-        return (zp + state.y) & 0xff;
-    }
-
     /*
-     * Perform a busy-loop for CLOCK_IN_NS nanoseconds
+     * Perform a busy-loop until the instruction should complete on the wall clock
      */
     private void delayLoop(int opcode) {
-        int clockSteps = Cpu.instructionClocks[0xff & opcode];
+        final int clockSteps;
-        // Just a precaution. This could be better.
+
+        if (behavior == CpuBehavior.NMOS_WITH_ROR_BUG ||
+            behavior == CpuBehavior.NMOS_6502) {
+            clockSteps = Cpu.instructionClocksNmos[0xff & opcode];
+        } else {
+            clockSteps = Cpu.instructionClocksCmos[0xff & opcode];
+        }
+
         if (clockSteps == 0) {
-            clockSteps = 1;
+            logger.warn("Opcode {} has clock step of 0!", String.format("0x%02x", opcode));
-        }
+            return;
-        long opScheduledEnd = opBeginTime + clockSteps;
-        long now = System.nanoTime();
-        while(now < opScheduledEnd) {
-            now = System.nanoTime();
-        }
         }
 
+        long interval = clockSteps * clockPeriodInNs;
+        long end;
 
-    /**
+        do {
-     * A compact, struct-like representation of CPU state.
+            end = System.nanoTime();
-     */
+        } while (opBeginTime + interval >= end);
-    public static class CpuState {
-        /**
-         * Accumulator
-         */
-        public int a;
-        /**
-         * X index regsiter
-         */
-        public int x;
-        /**
-         * Y index register
-         */
-        public int y;
-        /**
-         * Stack Pointer
-         */
-        public int sp;
-        /**
-         * Program Counter
-         */
-        public int pc;
-        /**
-         * Instruction Register
-         */
-        public int ir;
-        public int lastPc;
-        public int[] args = new int[2];
-        public int instSize;
-        public boolean opTrap;
-        public boolean irqAsserted;
-        public boolean nmiAsserted;
-
-        /* Status Flag Register bits */
-        public boolean carryFlag;
-        public boolean negativeFlag;
-        public boolean zeroFlag;
-        public boolean irqDisableFlag;
-        public boolean decimalModeFlag;
-        public boolean breakFlag;
-        public boolean overflowFlag;
-        public long stepCounter = 0L;
-
-        /**
-         * Create an empty CPU State.
-         */
-        public CpuState() {}
-
-        /**
-         * Snapshot a copy of the CpuState.
-         *
-         * (This is a copy constructor rather than an implementation of <code>Clonable</code>
-         * based on Josh Bloch's recommendation)
-         *
-         * @param s The CpuState to copy.
-         */
-        public CpuState(CpuState s) {
-            this.a = s.a;
-            this.x = s.x;
-            this.y = s.y;
-            this.sp = s.sp;
-            this.pc = s.pc;
-            this.ir = s.ir;
-            this.lastPc = s.lastPc;
-            this.args[0] = s.args[0];
-            this.args[1] = s.args[1];
-            this.instSize = s.instSize;
-            this.opTrap = s.opTrap;
-            this.irqAsserted = s.irqAsserted;
-            this.carryFlag = s.carryFlag;
-            this.negativeFlag = s.negativeFlag;
-            this.zeroFlag = s.zeroFlag;
-            this.irqDisableFlag = s.irqDisableFlag;
-            this.decimalModeFlag = s.decimalModeFlag;
-            this.breakFlag = s.breakFlag;
-            this.overflowFlag = s.overflowFlag;
-            this.stepCounter = s.stepCounter;
     }
 
     /**
-         * Returns a string formatted for the trace log.
+     * Return a formatted string representing the last instruction and
-         *
+     * operands that were executed.
-         * @return a string formatted for the trace log.
-         */
-        public String toTraceEvent() {
-            String opcode = disassembleOp();
-            StringBuilder sb = new StringBuilder(getInstructionByteStatus());
-            sb.append("  ");
-            sb.append(String.format("%-14s", opcode));
-            sb.append("A:" + HexUtil.byteToHex(a) + " ");
-            sb.append("X:" + HexUtil.byteToHex(x) + " ");
-            sb.append("Y:" + HexUtil.byteToHex(y) + " ");
-            sb.append("F:" + HexUtil.byteToHex(getStatusFlag()) + " ");
-            sb.append("S:1" + HexUtil.byteToHex(sp) + " ");
-            sb.append(getProcessorStatusString() + "\n");
-            return sb.toString();
-        }
-
-        /**
-         * @returns The value of the Process Status Register, as a byte.
-         */
-        public int getStatusFlag() {
-            int status = 0x20;
-            if (carryFlag) {
-                status |= P_CARRY;
-            }
-            if (zeroFlag) {
-                status |= P_ZERO;
-            }
-            if (irqDisableFlag) {
-                status |= P_IRQ_DISABLE;
-            }
-            if (decimalModeFlag) {
-                status |= P_DECIMAL;
-            }
-            if (breakFlag) {
-                status |= P_BREAK;
-            }
-            if (overflowFlag) {
-                status |= P_OVERFLOW;
-            }
-            if (negativeFlag) {
-                status |= P_NEGATIVE;
-            }
-            return status;
-        }
-
-        public String getInstructionByteStatus() {
-            switch (Cpu.instructionSizes[ir]) {
-                case 0:
-                case 1:
-                    return HexUtil.wordToHex(lastPc) + "  " +
-                           HexUtil.byteToHex(ir) + "      ";
-                case 2:
-                    return HexUtil.wordToHex(lastPc) + "  " +
-                           HexUtil.byteToHex(ir) + " " +
-                           HexUtil.byteToHex(args[0]) + "   ";
-                case 3:
-                    return HexUtil.wordToHex(lastPc) + "  " +
-                           HexUtil.byteToHex(ir) + " " +
-                           HexUtil.byteToHex(args[0]) + " " +
-                           HexUtil.byteToHex(args[1]);
-                default:
-                    return null;
-            }
-        }
-
-
-        /**
-         * Given an opcode and its operands, return a formatted name.
      *
      * @return A string representing the mnemonic and operands of the instruction
      */
-        public String disassembleOp() {
+    public static String disassembleOp(int opCode, int[] args) {
-            String mnemonic = opcodeNames[ir];
+        String mnemonic = opcodeNames[opCode];
 
         if (mnemonic == null) {
             return "???";
@@ -1498,37 +1440,37 @@ public class Cpu implements InstructionTable {
 
         StringBuilder sb = new StringBuilder(mnemonic);
 
-            switch (instructionModes[ir]) {
+        switch (instructionModes[opCode]) {
             case ABS:
-                    sb.append(" $" + HexUtil.wordToHex(address(args[0], args[1])));
+                sb.append(" $").append(Utils.wordToHex(Utils.address(args[0], args[1])));
                 break;
             case ABX:
-                    sb.append(" $" + HexUtil.wordToHex(address(args[0], args[1])) + ",X");
+                sb.append(" $").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(",X");
                 break;
             case ABY:
-                    sb.append(" $" + HexUtil.wordToHex(address(args[0], args[1])) + ",Y");
+                sb.append(" $").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(",Y");
                 break;
             case IMM:
-                    sb.append(" #$" + HexUtil.byteToHex(args[0]));
+                sb.append(" #$").append(Utils.byteToHex(args[0]));
                 break;
             case IND:
-                    sb.append(" ($" + HexUtil.wordToHex(address(args[0], args[1])) + ")");
+                sb.append(" ($").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(")");
                 break;
             case XIN:
-                    sb.append(" ($" + HexUtil.byteToHex(args[0]) + ",X)");
+                sb.append(" ($").append(Utils.byteToHex(args[0])).append(",X)");
                 break;
             case INY:
-                    sb.append(" ($" + HexUtil.byteToHex(args[0]) + "),Y");
+                sb.append(" ($").append(Utils.byteToHex(args[0])).append("),Y");
                 break;
             case REL:
             case ZPG:
-                    sb.append(" $" + HexUtil.byteToHex(args[0]));
+                sb.append(" $").append(Utils.byteToHex(args[0]));
                 break;
             case ZPX:
-                    sb.append(" $" + HexUtil.byteToHex(args[0]) + ",X");
+                sb.append(" $").append(Utils.byteToHex(args[0])).append(",X");
                 break;
             case ZPY:
-                    sb.append(" $" + HexUtil.byteToHex(args[0]) + ",Y");
+                sb.append(" $").append(Utils.byteToHex(args[0])).append(",Y");
                 break;
         }
 
@@ -1536,28 +1478,28 @@ public class Cpu implements InstructionTable {
     }
 
     /**
-         * Given two bytes, return an address.
+     * Return a formatted string representing the next instruction and
+     * operands to be executed.
+     *
+     * @return A string representing the mnemonic and operands of the instruction
      */
-        private int address(int lowByte, int hiByte) {
+    public String disassembleNextOp() {
-            return ((hiByte << 8) | lowByte) & 0xffff;
+        return Cpu.disassembleOp(state.nextIr, state.nextArgs);
     }
 
-
     /**
-         * @return A string representing the current status register state.
+     * @param address Address to disassemble
+     * @return String containing the disassembled instruction and operands.
      */
-        public String getProcessorStatusString() {
+    public String disassembleOpAtAddress(int address) throws MemoryAccessException {
-            StringBuilder sb = new StringBuilder("[");
+        int opCode = bus.read(address);
-            sb.append(negativeFlag ? 'N' : '.');    // Bit 7
+        int args[] = new int[2];
-            sb.append(overflowFlag ? 'V' : '.');    // Bit 6
+        int size = Cpu.instructionSizes[opCode];
-            sb.append("-");                         // Bit 5 (always 1)
+        for (int i = 1; i < size; i++) {
-            sb.append(breakFlag ? 'B' : '.');       // Bit 4
+            int nextRead = (address + i) % bus.endAddress();
-            sb.append(decimalModeFlag ? 'D' : '.'); // Bit 3
+            args[i-1] = bus.read(nextRead);
-            sb.append(irqDisableFlag ? 'I' : '.');  // Bit 2
-            sb.append(zeroFlag ? 'Z' : '.');        // Bit 1
-            sb.append(carryFlag ? 'C' : '.');       // Bit 0
-            sb.append("]");
-            return sb.toString();
         }
+
+        return disassembleOp(opCode, args);
     }
 }

src/main/java/com/loomcom/symon/CpuState.java

@@ -0,0 +1,177 @@
+package com.loomcom.symon;
+
+import com.loomcom.symon.util.Utils;
+
+/**
+ * A compact, struct-like representation of CPU state.
+ */
+public class CpuState {
+    /**
+     * Accumulator
+     */
+    public int a;
+
+    /**
+     * X index regsiter
+     */
+    public int x;
+
+    /**
+     * Y index register
+     */
+    public int y;
+
+    /**
+     * Stack Pointer
+     */
+    public int sp;
+
+    /**
+     * Program Counter
+     */
+    public int pc;
+
+    /**
+     * Last Loaded Instruction Register
+     */
+    public int ir;
+
+    /**
+     * Peek-Ahead to next IR
+     */
+    public int nextIr;
+    public int[] args = new int[2];
+    public int[] nextArgs = new int[2];
+    public int instSize;
+    public boolean opTrap;
+    public boolean irqAsserted;
+    public boolean nmiAsserted;
+    public int lastPc;
+
+    /* Status Flag Register bits */
+    public boolean carryFlag;
+    public boolean negativeFlag;
+    public boolean zeroFlag;
+    public boolean irqDisableFlag;
+    public boolean decimalModeFlag;
+    public boolean breakFlag;
+    public boolean overflowFlag;
+    public long stepCounter = 0L;
+
+    public CpuState() {}
+
+    /**
+     * Snapshot a copy of the CpuState.
+     *
+     * (This is a copy constructor rather than an implementation of <code>Cloneable</code>
+     * based on Josh Bloch's recommendation)
+     *
+     * @param s The CpuState to copy.
+     */
+    public CpuState(CpuState s) {
+        this.a = s.a;
+        this.x = s.x;
+        this.y = s.y;
+        this.sp = s.sp;
+        this.pc = s.pc;
+        this.ir = s.ir;
+        this.nextIr = s.nextIr;
+        this.lastPc = s.lastPc;
+        this.args[0] = s.args[0];
+        this.args[1] = s.args[1];
+        this.nextArgs[0] = s.nextArgs[0];
+        this.nextArgs[1] = s.nextArgs[1];
+        this.instSize = s.instSize;
+        this.opTrap = s.opTrap;
+        this.irqAsserted = s.irqAsserted;
+        this.carryFlag = s.carryFlag;
+        this.negativeFlag = s.negativeFlag;
+        this.zeroFlag = s.zeroFlag;
+        this.irqDisableFlag = s.irqDisableFlag;
+        this.decimalModeFlag = s.decimalModeFlag;
+        this.breakFlag = s.breakFlag;
+        this.overflowFlag = s.overflowFlag;
+        this.stepCounter = s.stepCounter;
+    }
+
+    /**
+     * Returns a string formatted for the trace log.
+     *
+     * @return a string formatted for the trace log.
+     */
+    public String toTraceEvent() {
+        String opcode = Cpu.disassembleOp(ir, args);
+        return getInstructionByteStatus() + "  " +
+                String.format("%-14s", opcode) +
+                "A:" + Utils.byteToHex(a) + " " +
+                "X:" + Utils.byteToHex(x) + " " +
+                "Y:" + Utils.byteToHex(y) + " " +
+                "F:" + Utils.byteToHex(getStatusFlag()) + " " +
+                "S:1" + Utils.byteToHex(sp) + " " +
+                getProcessorStatusString() + "\n";
+    }
+
+    /**
+     * @return The value of the Process Status Register, as a byte.
+     */
+    public int getStatusFlag() {
+        int status = 0x20;
+        if (carryFlag) {
+            status |= Cpu.P_CARRY;
+        }
+        if (zeroFlag) {
+            status |= Cpu.P_ZERO;
+        }
+        if (irqDisableFlag) {
+            status |= Cpu.P_IRQ_DISABLE;
+        }
+        if (decimalModeFlag) {
+            status |= Cpu.P_DECIMAL;
+        }
+        if (breakFlag) {
+            status |= Cpu.P_BREAK;
+        }
+        if (overflowFlag) {
+            status |= Cpu.P_OVERFLOW;
+        }
+        if (negativeFlag) {
+            status |= Cpu.P_NEGATIVE;
+        }
+        return status;
+    }
+
+    public String getInstructionByteStatus() {
+        switch (Cpu.instructionSizes[ir]) {
+            case 0:
+            case 1:
+                return Utils.wordToHex(lastPc) + "  " +
+                       Utils.byteToHex(ir) + "      ";
+            case 2:
+                return Utils.wordToHex(lastPc) + "  " +
+                       Utils.byteToHex(ir) + " " +
+                       Utils.byteToHex(args[0]) + "   ";
+            case 3:
+                return Utils.wordToHex(lastPc) + "  " +
+                       Utils.byteToHex(ir) + " " +
+                       Utils.byteToHex(args[0]) + " " +
+                       Utils.byteToHex(args[1]);
+            default:
+                return null;
+        }
+    }
+
+    /**
+     * @return A string representing the current status register state.
+     */
+    public String getProcessorStatusString() {
+        return "[" + (negativeFlag ? 'N' : '.') +
+                (overflowFlag ? 'V' : '.') +
+                "-" +
+                (breakFlag ? 'B' : '.') +
+                (decimalModeFlag ? 'D' : '.') +
+                (irqDisableFlag ? 'I' : '.') +
+                (zeroFlag ? 'Z' : '.') +
+                (carryFlag ? 'C' : '.') +
+                "]";
+    }
+}

src/main/java/com/loomcom/symon/InstructionTable.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2012 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -31,7 +31,7 @@ public interface InstructionTable {
      *
      * TODO: As of version 0.6, this is still not used! All CPUs are "idealized" NMOS 6502 only.
      */
-    public enum CpuBehavior {
+    enum CpuBehavior {
         /**
          * The earliest NMOS 6502 includes a bug that causes the ROR instruction
          * to behave like an ASL that does not affect the carry bit. This version
@@ -46,26 +46,23 @@ public interface InstructionTable {
          *
          * NB: Does NOT implement "unimplemented" NMOS instructions.
          */
-        NMOS_WITH_INDIRECT_JMP_BUG,
+        NMOS_6502,
-
-        /**
-         * Emulate an NMOS 6502 without the indirect JMP bug. This type of 6502
-         * does not actually exist in the wild.
-         *
-         * NB: Does NOT implement "unimplemented" NMOS instructions.
-         */
-        NMOS_WITHOUT_INDIRECT_JMP_BUG,
 
         /**
          * Emulate a CMOS 65C02, with all CMOS instructions and addressing modes.
          */
-        CMOS
+        CMOS_6502,
+
+        /**
+         * Emulate a CMOS 65C816.
+         */
+        CMOS_65816
     }
 
     /**
      * Enumeration of Addressing Modes.
      */
-    public enum Mode {
+    enum Mode {
         ACC {
             public String toString() {
                 return "Accumulator";
@@ -128,19 +125,25 @@ public interface InstructionTable {
 
         ZPG {
             public String toString() {
-                return "Zeropage";
+                return "Zero Page";
             }
         },
 
         ZPX {
             public String toString() {
-                return "Zeropage, X-indexed";
+                return "Zero Page, X-indexed";
             }
         },
 
         ZPY {
             public String toString() {
-                return "Zeropage, Y-indexed";
+                return "Zero Page, Y-indexed";
+            }
+        },
+
+        ZPI {
+            public String toString() {
+                return "Zero Page Indirect";
             }
         },
 
@@ -154,52 +157,55 @@ public interface InstructionTable {
     // 6502 opcodes.  No 65C02 opcodes implemented.
 
     /**
-     * Instruction opcode names.
+     * Instruction opcode names. This lists all opcodes for
+     * NMOS 6502, CMOS 65C02, and CMOS 65C816
      */
-    public static final String[] opcodeNames = {
+    String[] opcodeNames = {
-        "BRK", "ORA",  null,  null,  null, "ORA", "ASL",  null,
+        "BRK", "ORA",  null,  null,  null, "ORA", "ASL",  null,  // 0x00-0x07
-        "PHP", "ORA", "ASL",  null,  null, "ORA", "ASL",  null,
+        "PHP", "ORA", "ASL",  null,  null, "ORA", "ASL",  null,  // 0x08-0x0f
-        "BPL", "ORA",  null,  null,  null, "ORA", "ASL",  null,
+        "BPL", "ORA", "ORA",  null,  null, "ORA", "ASL",  null,  // 0x10-0x17
-        "CLC", "ORA",  null,  null,  null, "ORA", "ASL",  null,
+        "CLC", "ORA",  null,  null,  null, "ORA", "ASL",  null,  // 0x18-0x1f
-        "JSR", "AND",  null,  null, "BIT", "AND", "ROL",  null,
+        "JSR", "AND",  null,  null, "BIT", "AND", "ROL",  null,  // 0x20-0x27
-        "PLP", "AND", "ROL",  null, "BIT", "AND", "ROL",  null,
+        "PLP", "AND", "ROL",  null, "BIT", "AND", "ROL",  null,  // 0x28-0x2f
-        "BMI", "AND",  null,  null,  null, "AND", "ROL",  null,
+        "BMI", "AND", "AND",  null,  null, "AND", "ROL",  null,  // 0x30-0x37
-        "SEC", "AND",  null,  null,  null, "AND", "ROL",  null,
+        "SEC", "AND",  null,  null,  null, "AND", "ROL",  null,  // 0x38-0x3f
-        "RTI", "EOR",  null,  null,  null, "EOR", "LSR",  null,
+        "RTI", "EOR",  null,  null,  null, "EOR", "LSR",  null,  // 0x40-0x47
-        "PHA", "EOR", "LSR",  null, "JMP", "EOR", "LSR",  null,
+        "PHA", "EOR", "LSR",  null, "JMP", "EOR", "LSR",  null,  // 0x48-0x4f
-        "BVC", "EOR",  null,  null,  null, "EOR", "LSR",  null,
+        "BVC", "EOR", "EOR",  null,  null, "EOR", "LSR",  null,  // 0x50-0x57
-        "CLI", "EOR",  null,  null,  null, "EOR", "LSR",  null,
+        "CLI", "EOR",  null,  null,  null, "EOR", "LSR",  null,  // 0x58-0x5f
-        "RTS", "ADC",  null,  null,  null, "ADC", "ROR",  null,
+        "RTS", "ADC",  null,  null,  null, "ADC", "ROR",  null,  // 0x60-0x67
-        "PLA", "ADC", "ROR",  null, "JMP", "ADC", "ROR",  null,
+        "PLA", "ADC", "ROR",  null, "JMP", "ADC", "ROR",  null,  // 0x68-0x6f
-        "BVS", "ADC",  null,  null,  null, "ADC", "ROR",  null,
+        "BVS", "ADC", "ADC",  null,  null, "ADC", "ROR",  null,  // 0x70-0x77
-        "SEI", "ADC",  null,  null,  null, "ADC", "ROR",  null,
+        "SEI", "ADC",  null,  null, "JMP", "ADC", "ROR",  null,  // 0x78-0x7f
-        "BCS", "STA",  null,  null, "STY", "STA", "STX",  null,
+        "BCS", "STA",  null,  null, "STY", "STA", "STX",  null,  // 0x80-0x87
-        "DEY",  null, "TXA",  null, "STY", "STA", "STX",  null,
+        "DEY",  null, "TXA",  null, "STY", "STA", "STX",  null,  // 0x88-0x8f
-        "BCC", "STA",  null,  null, "STY", "STA", "STX",  null,
+        "BCC", "STA", "STA",  null, "STY", "STA", "STX",  null,  // 0x90-0x97
-        "TYA", "STA", "TXS",  null,  null, "STA",  null,  null,
+        "TYA", "STA", "TXS",  null,  null, "STA",  null,  null,  // 0x98-0x9f
-        "LDY", "LDA", "LDX",  null, "LDY", "LDA", "LDX",  null,
+        "LDY", "LDA", "LDX",  null, "LDY", "LDA", "LDX",  null,  // 0xa0-0xa7
-        "TAY", "LDA", "TAX",  null, "LDY", "LDA", "LDX",  null,
+        "TAY", "LDA", "TAX",  null, "LDY", "LDA", "LDX",  null,  // 0xa8-0xaf
-        "BCS", "LDA",  null,  null, "LDY", "LDA", "LDX",  null,
+        "BCS", "LDA", "LDA",  null, "LDY", "LDA", "LDX",  null,  // 0xb0-0xb7
-        "CLV", "LDA", "TSX",  null, "LDY", "LDA", "LDX",  null,
+        "CLV", "LDA", "TSX",  null, "LDY", "LDA", "LDX",  null,  // 0xb8-0xbf
-        "CPY", "CMP",  null,  null, "CPY", "CMP", "DEC",  null,
+        "CPY", "CMP",  null,  null, "CPY", "CMP", "DEC",  null,  // 0xc0-0xc7
-        "INY", "CMP", "DEX",  null, "CPY", "CMP", "DEC",  null,
+        "INY", "CMP", "DEX",  null, "CPY", "CMP", "DEC",  null,  // 0xc8-0xcf
-        "BNE", "CMP",  null,  null,  null, "CMP", "DEC",  null,
+        "BNE", "CMP", "CMP",  null,  null, "CMP", "DEC",  null,  // 0xd0-0xd7
-        "CLD", "CMP",  null,  null,  null, "CMP", "DEC",  null,
+        "CLD", "CMP",  null,  null,  null, "CMP", "DEC",  null,  // 0xd8-0xdf
-        "CPX", "SBC",  null,  null, "CPX", "SBC", "INC",  null,
+        "CPX", "SBC",  null,  null, "CPX", "SBC", "INC",  null,  // 0xe0-0xe7
-        "INX", "SBC", "NOP",  null, "CPX", "SBC", "INC",  null,
+        "INX", "SBC", "NOP",  null, "CPX", "SBC", "INC",  null,  // 0xe8-0xef
-        "BEQ", "SBC",  null,  null,  null, "SBC", "INC",  null,
+        "BEQ", "SBC", "SBC",  null,  null, "SBC", "INC",  null,  // 0xf0-0xf7
-        "SED", "SBC",  null,  null,  null, "SBC", "INC",  null
+        "SED", "SBC",  null,  null,  null, "SBC", "INC",  null   // 0xf8-0xff
     };
 
     /**
-     * Instruction addressing modes.
+     * Instruction addressing modes. This table includes sizes
+     * for all instructions for NMOS 6502, CMOS 65C02,
+     * and CMOS 65C816
      */
-    public static final Mode[] instructionModes = {
+    Mode[] instructionModes = {
         Mode.IMP, Mode.XIN, Mode.NUL, Mode.NUL,   // 0x00-0x03
         Mode.NUL, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x04-0x07
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x08-0x0b
         Mode.NUL, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x0c-0x0f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x10-0x13
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x10-0x13
         Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x14-0x17
         Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x18-0x1b
         Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x1c-0x1f
@@ -207,7 +213,7 @@ public interface InstructionTable {
         Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x24-0x27
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x28-0x2b
         Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x2c-0x2f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x30-0x33
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x30-0x33
         Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x34-0x37
         Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x38-0x3b
         Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x3c-0x3f
@@ -215,7 +221,7 @@ public interface InstructionTable {
         Mode.NUL, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x44-0x47
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x48-0x4b
         Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x4c-0x4f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x50-0x53
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x50-0x53
         Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x54-0x57
         Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x58-0x5b
         Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x5c-0x5f
@@ -223,15 +229,15 @@ public interface InstructionTable {
         Mode.NUL, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x64-0x67
         Mode.IMP, Mode.IMM, Mode.ACC, Mode.NUL,   // 0x68-0x6b
         Mode.IND, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x6c-0x6f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x70-0x73
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x70-0x73
         Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0x74-0x77
         Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0x78-0x7b
-        Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x7c-0x7f
+        Mode.ABX, Mode.ABX, Mode.ABX, Mode.NUL,   // 0x7c-0x7f
         Mode.REL, Mode.XIN, Mode.NUL, Mode.NUL,   // 0x80-0x83
         Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0x84-0x87
         Mode.IMP, Mode.NUL, Mode.IMP, Mode.NUL,   // 0x88-0x8b
         Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0x8c-0x8f
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0x90-0x93
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0x90-0x93
         Mode.ZPX, Mode.ZPX, Mode.ZPY, Mode.NUL,   // 0x94-0x97
         Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0x98-0x9b
         Mode.NUL, Mode.ABX, Mode.NUL, Mode.NUL,   // 0x9c-0x9f
@@ -239,7 +245,7 @@ public interface InstructionTable {
         Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0xa4-0xa7
         Mode.IMP, Mode.IMM, Mode.IMP, Mode.NUL,   // 0xa8-0xab
         Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0xac-0xaf
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0xb0-0xb3
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0xb0-0xb3
         Mode.ZPX, Mode.ZPX, Mode.ZPY, Mode.NUL,   // 0xb4-0xb7
         Mode.IMP, Mode.ABY, Mode.IMP, Mode.NUL,   // 0xb8-0xbb
         Mode.ABX, Mode.ABX, Mode.ABY, Mode.NUL,   // 0xbc-0xbf
@@ -247,7 +253,7 @@ public interface InstructionTable {
         Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0xc4-0xc7
         Mode.IMP, Mode.IMM, Mode.IMP, Mode.NUL,   // 0xc8-0xcb
         Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0xcc-0xcf
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0xd0-0xd3
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0xd0-0xd3
         Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0xd4-0xd7
         Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0xd8-0xdb
         Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL,   // 0xdc-0xdf
@@ -255,7 +261,7 @@ public interface InstructionTable {
         Mode.ZPG, Mode.ZPG, Mode.ZPG, Mode.NUL,   // 0xe4-0xe7
         Mode.IMP, Mode.IMM, Mode.IMP, Mode.NUL,   // 0xe8-0xeb
         Mode.ABS, Mode.ABS, Mode.ABS, Mode.NUL,   // 0xec-0xef
-        Mode.REL, Mode.INY, Mode.NUL, Mode.NUL,   // 0xf0-0xf3
+        Mode.REL, Mode.INY, Mode.ZPI, Mode.NUL,   // 0xf0-0xf3
         Mode.NUL, Mode.ZPX, Mode.ZPX, Mode.NUL,   // 0xf4-0xf7
         Mode.IMP, Mode.ABY, Mode.NUL, Mode.NUL,   // 0xf8-0xfb
         Mode.NUL, Mode.ABX, Mode.ABX, Mode.NUL    // 0xfc-0xff
@@ -263,47 +269,73 @@ public interface InstructionTable {
 
 
     /**
-     * Size, in bytes, required for each instruction.
+     * Size, in bytes, required for each instruction. This table
+     * includes sizes for all instructions for NMOS 6502, CMOS 65C02,
+     * and CMOS 65C816
      */
-    public static final int[] instructionSizes = {
+    int[] instructionSizes = {
-        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 0, 3, 3, 0,
+        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 0, 3, 3, 0,   // 0x00-0x0f
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
+        2, 2, 2, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,   // 0x10-0x1f
-        3, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
+        3, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,   // 0x20-0x2f
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
+        2, 2, 2, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,   // 0x30-0x3f
-        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
+        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,   // 0x40-0x4f
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
+        2, 2, 2, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,   // 0x50-0x5f
-        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
+        1, 2, 0, 0, 0, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,   // 0x60-0x6f
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
+        2, 2, 2, 0, 0, 2, 2, 0, 1, 3, 0, 0, 3, 3, 3, 0,   // 0x70-0x7f
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 0, 1, 0, 3, 3, 3, 0,
+        2, 2, 0, 0, 2, 2, 2, 0, 1, 0, 1, 0, 3, 3, 3, 0,   // 0x80-0x8f
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 3, 1, 0, 0, 3, 0, 0,
+        2, 2, 2, 0, 2, 2, 2, 0, 1, 3, 1, 0, 0, 3, 0, 0,   // 0x90-0x9f
-        2, 2, 2, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
+        2, 2, 2, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,   // 0xa0-0xaf
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 3, 1, 0, 3, 3, 3, 0,
+        2, 2, 2, 0, 2, 2, 2, 0, 1, 3, 1, 0, 3, 3, 3, 0,   // 0xb0-0xbf
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
+        2, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,   // 0xc0-0xcf
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,
+        2, 2, 2, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0,   // 0xd0-0xdf
-        2, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,
+        2, 2, 0, 0, 2, 2, 2, 0, 1, 2, 1, 0, 3, 3, 3, 0,   // 0xe0-0xef
-        2, 2, 0, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0
+        2, 2, 2, 0, 0, 2, 2, 0, 1, 3, 0, 0, 0, 3, 3, 0    // 0xf0-0xff
     };
 
     /**
-     * Number of clock cycles required for each instruction
+     * Number of clock cycles required for each instruction when
+     * in NMOS mode.
      */
-    public static final int[] instructionClocks = {
+    int[] instructionClocksNmos = {
-        7, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 0, 4, 6, 0,
+        7, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 0, 4, 6, 0,   // 0x00-0x0f
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
+        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x10-0x1f
-        6, 6, 0, 0, 3, 3, 5, 0, 4, 2, 2, 0, 4, 4, 6, 0,
+        6, 6, 0, 0, 3, 3, 5, 0, 4, 2, 2, 0, 4, 4, 6, 0,   // 0x20-0x2f
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
+        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x30-0x3f
-        6, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 3, 4, 6, 0,
+        6, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 3, 4, 6, 0,   // 0x40-0x4f
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
+        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x50-0x5f
-        6, 6, 0, 0, 0, 3, 5, 0, 4, 2, 2, 0, 5, 4, 6, 0,
+        6, 6, 0, 0, 0, 3, 5, 0, 4, 2, 2, 0, 5, 4, 6, 0,   // 0x60-0x6f
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
+        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x70-0x7f
-        2, 6, 0, 0, 3, 3, 3, 0, 2, 0, 2, 0, 4, 4, 4, 0,
+        2, 6, 0, 0, 3, 3, 3, 0, 2, 0, 2, 0, 4, 4, 4, 0,   // 0x80-0x8f
-        2, 6, 0, 0, 4, 4, 4, 0, 2, 5, 2, 0, 0, 5, 0, 0,
+        2, 6, 0, 0, 4, 4, 4, 0, 2, 5, 2, 0, 0, 5, 0, 0,   // 0x90-0x9f
-        2, 6, 2, 0, 3, 3, 3, 0, 2, 2, 2, 0, 4, 4, 4, 0,
+        2, 6, 2, 0, 3, 3, 3, 0, 2, 2, 2, 0, 4, 4, 4, 0,   // 0xa0-0xaf
-        2, 5, 0, 0, 4, 4, 4, 0, 2, 4, 2, 0, 4, 4, 4, 0,
+        2, 5, 0, 0, 4, 4, 4, 0, 2, 4, 2, 0, 4, 4, 4, 0,   // 0xb0-0xbf
-        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,
+        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,   // 0xc0-0xcf
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,
+        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0xd0-0xdf
-        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,
+        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,   // 0xe0-0xef
-        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0
+        2, 5, 0, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0    // 0xf0-0xff
+    };
+
+    /**
+     * Number of clock cycles required for each instruction when
+     * in CMOS mode
+     */
+    int[] instructionClocksCmos = {
+        7, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 0, 4, 6, 0,   // 0x00-0x0f
+        2, 5, 5, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x10-0x1f
+        6, 6, 0, 0, 3, 3, 5, 0, 4, 2, 2, 0, 4, 4, 6, 0,   // 0x20-0x2f
+        2, 5, 5, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x30-0x3f
+        6, 6, 0, 0, 0, 3, 5, 0, 3, 2, 2, 0, 3, 4, 6, 0,   // 0x40-0x4f
+        2, 5, 5, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x50-0x5f
+        6, 6, 0, 0, 0, 3, 5, 0, 4, 2, 2, 0, 5, 4, 6, 0,   // 0x60-0x6f
+        2, 5, 5, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0x70-0x7f
+        2, 6, 0, 0, 3, 3, 3, 0, 2, 0, 2, 0, 4, 4, 4, 0,   // 0x80-0x8f
+        2, 6, 5, 0, 4, 4, 4, 0, 2, 5, 2, 0, 0, 5, 0, 0,   // 0x90-0x9f
+        2, 6, 2, 0, 3, 3, 3, 0, 2, 2, 2, 0, 4, 4, 4, 0,   // 0xa0-0xaf
+        2, 5, 5, 0, 4, 4, 4, 0, 2, 4, 2, 0, 4, 4, 4, 0,   // 0xb0-0xbf
+        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,   // 0xc0-0xcf
+        2, 5, 5, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0,   // 0xd0-0xdf
+        2, 6, 0, 0, 3, 3, 5, 0, 2, 2, 2, 0, 4, 4, 6, 0,   // 0xe0-0xef
+        2, 5, 5, 0, 0, 4, 6, 0, 2, 4, 0, 0, 0, 4, 7, 0    // 0xf0-0xff
     };
 
 }

src/main/java/com/loomcom/symon/Main.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *                    Maik Merten <maikmerten@googlemail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -39,7 +39,7 @@ public class Main {
      * Main entry point to the simulator. Creates a simulator and shows the main
      * window.
      *
-     * @param args
+     * @param args Program arguments
      */
     public static void main(String args[]) throws Exception {
         
@@ -48,12 +48,16 @@ public class Main {
             String arg = args[i].toLowerCase(Locale.ENGLISH);
             if(arg.equals("-machine") && (i+1) < args.length) {
                 String machine = args[i+1].trim().toLowerCase(Locale.ENGLISH);
-                if(machine.equals("symon")) {
+                switch (machine) {
+                    case "symon":
                         machineClass = SymonMachine.class;
-                } else if(machine.equals("multicomp")) {
+                        break;
+                    case "multicomp":
                         machineClass = MulticompMachine.class;
-                } else if (machine.equals("simple")) {
+                        break;
+                    case "simple":
                         machineClass = SimpleMachine.class;
+                        break;
                 }
             }
         }
@@ -83,6 +87,7 @@ public class Main {
             final Simulator simulator = new Simulator(machineClass);
         
             SwingUtilities.invokeLater(new Runnable() {
+                @Override
                 public void run() {
                     try {
                         UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
@@ -95,8 +100,8 @@ public class Main {
             });
         
         
-            Simulator.MAIN_CMD cmd = simulator.waitForCommand();
+            Simulator.MainCommand cmd = simulator.waitForCommand();
-            if (cmd.equals(Simulator.MAIN_CMD.SELECTMACHINE)) {
+            if (cmd.equals(Simulator.MainCommand.SELECTMACHINE)) {
                 machineClass = null;
             } else {
                 break;

src/main/java/com/loomcom/symon/MemoryRange.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -34,9 +34,13 @@ import com.loomcom.symon.exceptions.*;
  */
 public class MemoryRange implements Comparable<MemoryRange> {
 
-  /** The starting address of the memory range. */
+    /**
+     * The starting address of the memory range.
+     */
     public int startAddress;
-  /** The ending address of the memory range. */
+    /**
+     * The ending address of the memory range.
+     */
     public int endAddress;
 
     public MemoryRange(int startAddress, int endAddress)
@@ -53,14 +57,14 @@ public class MemoryRange implements Comparable<MemoryRange> {
     }
 
     /**
-   * @returns the starting address.
+     * @return the starting address.
      */
     public int startAddress() {
         return startAddress;
     }
 
     /**
-   * @returns the ending address.
+     * @return the ending address.
      */
     public int endAddress() {
         return endAddress;
@@ -69,7 +73,7 @@ public class MemoryRange implements Comparable<MemoryRange> {
     /**
      * Checks for address inclusion in the range.
      *
-   * @returns true if the address is included within this range,
+     * @return true if the address is included within this range,
      * false otherwise.
      */
     public boolean includes(int address) {
@@ -80,7 +84,7 @@ public class MemoryRange implements Comparable<MemoryRange> {
     /**
      * Checks for overlapping memory ranges.
      *
-   * @returns true if this range overlaps in any way with the other.
+     * @return true if this range overlaps in any way with the other.
      */
     public boolean overlaps(MemoryRange other) {
         return (this.includes(other.startAddress()) ||
@@ -95,16 +99,13 @@ public class MemoryRange implements Comparable<MemoryRange> {
         if (this == other) {
             return 0;
         }
-    Integer thisStartAddr = new Integer(this.startAddress());
+        Integer thisStartAddr = this.startAddress();
-    Integer thatStartAddr = new Integer(other.startAddress());
+        Integer thatStartAddr = other.startAddress();
         return thisStartAddr.compareTo(thatStartAddr);
     }
 
     public String toString() {
-    StringBuffer desc = new StringBuffer("@");
+        return "@" + String.format("0x%04x", startAddress) + "-" +
-    desc.append(String.format("0x%04x", startAddress));
+                String.format("0x%04x", endAddress);
-    desc.append("-");
-    desc.append(String.format("0x%04x", endAddress));
-    return desc.toString();
     }
 }

src/main/java/com/loomcom/symon/Preferences.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -27,15 +27,15 @@ import javax.swing.*;
 
 public interface Preferences {
 
-    public static final int DEFAULT_PROGRAM_LOAD_ADDRESS = 0x0300;
+    int DEFAULT_PROGRAM_LOAD_ADDRESS = 0x0300;
 
-    public static final boolean DEFAULT_HALT_ON_BREAK = true;
+    boolean DEFAULT_HALT_ON_BREAK = true;
 
-    public JDialog getDialog();
+    JDialog getDialog();
 
-    public int getProgramStartAddress();
+    int getProgramStartAddress();
 
-    public boolean getHaltOnBreak();
+    boolean getHaltOnBreak();
 
-    public void updateUi();
+    void updateUi();
 }

src/main/java/com/loomcom/symon/Simulator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyrighi (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -24,21 +24,20 @@
 package com.loomcom.symon;
 
 import com.loomcom.symon.devices.Memory;
-import com.loomcom.symon.exceptions.FifoUnderrunException;
+import com.loomcom.symon.exceptions.*;
-import com.loomcom.symon.exceptions.MemoryAccessException;
-import com.loomcom.symon.exceptions.MemoryRangeException;
-import com.loomcom.symon.exceptions.SymonException;
 import com.loomcom.symon.machines.Machine;
 import com.loomcom.symon.ui.*;
 import com.loomcom.symon.ui.Console;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import javax.swing.*;
 import javax.swing.border.EmptyBorder;
 import java.awt.*;
 import java.awt.event.*;
 import java.io.*;
-import java.util.logging.Level;
+import java.util.SortedSet;
-import java.util.logging.Logger;
+import java.util.TreeSet;
 
 /**
  * Symon Simulator Interface and Control.
@@ -50,11 +49,16 @@ import java.util.logging.Logger;
  */
 public class Simulator {
 
+    private final static Logger logger = LoggerFactory.getLogger(Simulator.class.getName());
+
     // UI constants
     private static final int DEFAULT_FONT_SIZE = 12;
     private static final Font DEFAULT_FONT = new Font(Font.MONOSPACED, Font.PLAIN, DEFAULT_FONT_SIZE);
     private static final int CONSOLE_BORDER_WIDTH = 10;
 
+    // Clock periods, in NS, for each speed. 0MHz, 1MHz, 2MHz, 3MHz, 4MHz, 5MHz, 6MHz, 7MHz, 8MHz.
+    private static final long[] CLOCK_PERIODS = {0, 1000, 500, 333, 250, 200, 167, 143, 125};
+
     // Since it is very expensive to update the UI with Swing's Event Dispatch Thread, we can't afford
     // to refresh the status view on every simulated clock cycle. Instead, we will only refresh the status view
     // after this number of steps when running normally.
@@ -66,14 +70,12 @@ public class Simulator {
     //
     private static final int MAX_STEPS_BETWEEN_UPDATES = 20000;
 
-    private final static Logger logger = Logger.getLogger(Simulator.class.getName());
-
     // The simulated machine
     private Machine machine;
 
     // Number of CPU steps between CRT repaints.
     // TODO: Dynamically refresh the value at runtime based on performance figures to reach ~ 30fps.
-    private long stepsBetweenCrtcRefreshes = 2500;
+    private static final long STEPS_BETWEEN_CRTC_REFRESHES = 2500;
 
     // A counter to keep track of the number of UI updates that have been
     // requested
@@ -93,14 +95,16 @@ public class Simulator {
     /**
      * The Trace Window shows the most recent 50,000 CPU states.
      */
-    private TraceLog traceLog;
+    private final TraceLog traceLog;
 
     /**
      * The Memory Window shows the contents of one page of memory.
      */
-    private MemoryWindow memoryWindow;
+    private final MemoryWindow memoryWindow;
 
-    private VideoWindow videoWindow;
+    private final VideoWindow videoWindow;
+
+    private final BreakpointsWindow breakpointsWindow;
 
     private SimulatorMenu menuBar;
 
@@ -110,16 +114,18 @@ public class Simulator {
 
     private JButton runStopButton;
     private JButton stepButton;
-    private JButton softResetButton;
-    private JButton hardResetButton;
     private JComboBox<String> stepCountBox;
 
     private JFileChooser fileChooser;
     private PreferencesDialog preferences;
 
+    private Breakpoints breakpoints;
+
     private final Object commandMonitorObject = new Object();
-    private MAIN_CMD command = MAIN_CMD.NONE;
+
-    public static enum MAIN_CMD  {
+    private MainCommand command = MainCommand.NONE;
+
+    public enum MainCommand {
         NONE,
         SELECTMACHINE
     }
@@ -130,7 +136,20 @@ public class Simulator {
     private static final String[] STEPS = {"1", "5", "10", "20", "50", "100"};
 
     public Simulator(Class machineClass) throws Exception {
+        this.breakpoints = new Breakpoints(this);
+
         this.machine = (Machine) machineClass.getConstructors()[0].newInstance();
+
+        // Initialize final fields in the constructor.
+        this.traceLog = new TraceLog();
+        this.memoryWindow = new MemoryWindow(machine.getBus());
+        this.breakpointsWindow = new BreakpointsWindow(breakpoints, mainWindow);
+
+        if (machine.getCrtc() != null) {
+            videoWindow = new VideoWindow(machine.getCrtc(), 2, 2);
+        } else {
+            videoWindow = null;
+        }
     }
 
     /**
@@ -143,7 +162,7 @@ public class Simulator {
         mainWindow.getContentPane().setLayout(new BorderLayout());
 
         // UI components used for I/O.
-        this.console = new com.loomcom.symon.ui.Console(80, 25, DEFAULT_FONT);
+        this.console = new com.loomcom.symon.ui.Console(80, 25, DEFAULT_FONT, false);
         this.statusPane = new StatusPanel(machine);
 
         console.setBorderWidth(CONSOLE_BORDER_WIDTH);
@@ -162,11 +181,12 @@ public class Simulator {
 
         runStopButton = new JButton("Run");
         stepButton = new JButton("Step");
-        softResetButton = new JButton("Soft Reset");
+        JButton softResetButton = new JButton("Soft Reset");
-        hardResetButton = new JButton("Hard Reset");
+        JButton hardResetButton = new JButton("Hard Reset");
 
-        stepCountBox = new JComboBox<String>(STEPS);
+        stepCountBox = new JComboBox<>(STEPS);
         stepCountBox.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
                 try {
                     JComboBox cb = (JComboBox) actionEvent.getSource();
@@ -195,47 +215,40 @@ public class Simulator {
         mainWindow.getContentPane().add(buttonContainer, BorderLayout.PAGE_END);
 
         runStopButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
                 if (runLoop != null && runLoop.isRunning()) {
-                    handleStop();
+                    Simulator.this.handleStop();
                 } else {
-                    handleStart();
+                    Simulator.this.handleStart();
                 }
             }
         });
 
         stepButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
-                handleStep(stepsPerClick);
+                Simulator.this.handleStep(stepsPerClick);
             }
         });
 
         softResetButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
                 // If this was a CTRL-click, do a hard reset.
-                handleReset(false);
+                Simulator.this.handleReset(false);
             }
         });
 
         hardResetButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
                 // If this was a CTRL-click, do a hard reset.
-                handleReset(true);
+                Simulator.this.handleReset(true);
             }
         });
 
-        // Prepare the log window
+        mainWindow.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
-        traceLog = new TraceLog();
-
-        // Prepare the memory window
-        memoryWindow = new MemoryWindow(machine.getBus());
-
-        // Composite Video and 6545 CRTC
-        if(machine.getCrtc() != null) {
-            videoWindow = new VideoWindow(machine.getCrtc(), 2, 2);
-        }
-
-        mainWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
         // The Menu. This comes last, because it relies on other components having
         // already been initialized.
@@ -249,7 +262,7 @@ public class Simulator {
         handleReset(false);
     }
 
-    public MAIN_CMD waitForCommand() {
+    public MainCommand waitForCommand() {
         synchronized (commandMonitorObject) {
             try {
                 commandMonitorObject.wait();
@@ -287,7 +300,7 @@ public class Simulator {
         }
 
         try {
-            logger.log(Level.INFO, "Reset requested. Resetting CPU.");
+            logger.debug("Reset requested. Resetting CPU.");
             // Reset CPU
             machine.getCpu().reset();
             // Clear the console.
@@ -302,15 +315,9 @@ public class Simulator {
                 }
             }
             // Update status.
-            SwingUtilities.invokeLater(new Runnable() {
+            updateVisibleState();
-                public void run() {
-                    // Now update the state
-                    statusPane.updateState();
-                    memoryWindow.updateState();
-                }
-            });
         } catch (MemoryAccessException ex) {
-            logger.log(Level.SEVERE, "Exception during simulator reset: " + ex.getMessage());
+            logger.error("Exception during simulator reset", ex);
         }
     }
 
@@ -322,17 +329,9 @@ public class Simulator {
             for (int i = 0; i < numSteps; i++) {
                 step();
             }
-            SwingUtilities.invokeLater(new Runnable() {
+            updateVisibleState();
-                public void run() {
-                    if (traceLog.isVisible()) {
-                        traceLog.refresh();
-                    }
-                    statusPane.updateState();
-                    memoryWindow.updateState();
-                }
-            });
         } catch (SymonException ex) {
-            logger.log(Level.SEVERE, "Exception during simulator step: " + ex.getMessage());
+            logger.error("Exception during simulator step", ex);
             ex.printStackTrace();
         }
     }
@@ -359,27 +358,23 @@ public class Simulator {
                 machine.getAcia().rxWrite((int) console.readInputChar());
             }
         } catch (FifoUnderrunException ex) {
-            logger.severe("Console type-ahead buffer underrun!");
+            logger.error("Console type-ahead buffer underrun!");
         }
 
-        if (videoWindow != null && stepsSinceLastCrtcRefresh++ > stepsBetweenCrtcRefreshes) {
+        if (videoWindow != null && stepsSinceLastCrtcRefresh++ > STEPS_BETWEEN_CRTC_REFRESHES) {
             stepsSinceLastCrtcRefresh = 0;
+            if (videoWindow.isVisible()) {
+                videoWindow.repaint();
+            }
         }
 
         // This is a very expensive update, and we're doing it without
         // a delay, so we don't want to overwhelm the Swing event processing thread
         // with requests. Limit the number of ui updates that can be performed.
         if (stepsSinceLastUpdate++ > MAX_STEPS_BETWEEN_UPDATES) {
-            SwingUtilities.invokeLater(new Runnable() {
+            updateVisibleState();
-                public void run() {
-                    // Now update the state
-                    statusPane.updateState();
-                    memoryWindow.updateState();
-                }
-            });
             stepsSinceLastUpdate = 0;
         }
-
     }
 
     /**
@@ -391,8 +386,7 @@ public class Simulator {
             machine.getBus().write(addr++, program[i] & 0xff);
         }
 
-        logger.log(Level.INFO, "Loaded " + i + " bytes at address 0x" +
+        logger.info("Loaded {} bytes at address 0x{}", i, Integer.toString(startAddress, 16));
-                               Integer.toString(startAddress, 16));
 
         // After loading, be sure to reset and
         // Reset (but don't clear memory, naturally)
@@ -402,15 +396,8 @@ public class Simulator {
         machine.getCpu().setProgramCounter(preferences.getProgramStartAddress());
 
         // Immediately update the UI.
-        SwingUtilities.invokeLater(new Runnable() {
+        updateVisibleState();
-            public void run() {
-                // Now update the state
-                statusPane.updateState();
-                memoryWindow.updateState();
     }
-        });
-    }
-
 
     /**
      * The main run thread.
@@ -427,10 +414,11 @@ public class Simulator {
         }
 
         public void run() {
-            logger.log(Level.INFO, "Starting main run loop.");
+            logger.debug("Starting main run loop.");
             isRunning = true;
 
             SwingUtilities.invokeLater(new Runnable() {
+                @Override
                 public void run() {
                     // Don't allow step while the simulator is running
                     stepButton.setEnabled(false);
@@ -446,11 +434,11 @@ public class Simulator {
                     step();
                 } while (shouldContinue());
             } catch (SymonException ex) {
-                logger.log(Level.SEVERE, "Exception in main simulator run thread. Exiting run.");
+                logger.error("Exception in main simulator run thread. Exiting run.", ex);
-                ex.printStackTrace();
             }
 
             SwingUtilities.invokeLater(new Runnable() {
+                @Override
                 public void run() {
                     statusPane.updateState();
                     memoryWindow.updateState();
@@ -469,15 +457,19 @@ public class Simulator {
         }
 
         /**
-         * Returns true if the run loop should proceed to the next step.
-         *
          * @return True if the run loop should proceed to the next step.
          */
         private boolean shouldContinue() {
-            return isRunning && !(preferences.getHaltOnBreak() && machine.getCpu().getInstruction() == 0x00);
+            return !breakpoints.contains(machine.getCpu().getProgramCounter()) &&
+                    isRunning &&
+                    !(preferences.getHaltOnBreak() && machine.getCpu().getInstruction() == 0x00);
         }
     }
 
+    public String disassembleOpAtAddress(int address) throws MemoryAccessException {
+        return machine.getCpu().disassembleOpAtAddress(address);
+    }
+
     class LoadProgramAction extends AbstractAction {
         public LoadProgramAction() {
             super("Load Program...", null);
@@ -508,14 +500,17 @@ public class Simulator {
                                 program[i++] = dis.readByte();
                             }
 
+                            // Now load the program at the starting address.
+                            loadProgram(program, preferences.getProgramStartAddress());
+
                             SwingUtilities.invokeLater(new Runnable() {
+                                @Override
                                 public void run() {
                                     console.reset();
+                                    breakpoints.refresh();
                                 }
                             });
 
-                            // Now load the program at the starting address.
-                            loadProgram(program, preferences.getProgramStartAddress());
                             // TODO: "Don't Show Again" checkbox
                             JOptionPane.showMessageDialog(mainWindow,
                                     "Loaded Successfully At " +
@@ -526,10 +521,10 @@ public class Simulator {
                     }
                 }
             } catch (IOException ex) {
-                logger.log(Level.SEVERE, "Unable to read program file: " + ex.getMessage());
+                logger.error("Unable to read program file.", ex);
                 JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             } catch (MemoryAccessException ex) {
-                logger.log(Level.SEVERE, "Memory access error loading program: " + ex.getMessage());
+                logger.error("Memory access error loading program", ex);
                 JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             }
         }
@@ -552,7 +547,7 @@ public class Simulator {
 
                         if (fileSize != machine.getRomSize()) {
                             throw new IOException("ROM file must be exactly " + String.valueOf(machine.getRomSize()) + " bytes.");
-                        } else {
+                        }
 
                         // Load the new ROM image
                         Memory rom = Memory.makeROM(machine.getRomBase(), machine.getRomBase() + machine.getRomSize() - 1, romFile);
@@ -561,7 +556,12 @@ public class Simulator {
                         // Now, reset
                         machine.getCpu().reset();
 
-                            logger.log(Level.INFO, "ROM File `" + romFile.getName() + "' loaded at " +
+                        updateVisibleState();
+
+                        // Refresh breakpoints to show new memory contents.
+                        breakpoints.refresh();
+
+                        logger.info("ROM File `{}' loaded at {}", romFile.getName(),
                                 String.format("0x%04X", machine.getRomBase()));
                         // TODO: "Don't Show Again" checkbox
                         JOptionPane.showMessageDialog(mainWindow,
@@ -569,17 +569,17 @@ public class Simulator {
                                         String.format("$%04X", machine.getRomBase()),
                                 "OK",
                                 JOptionPane.PLAIN_MESSAGE);
-                        }
+
                     }
                 }
             } catch (IOException ex) {
-                logger.log(Level.SEVERE, "Unable to read ROM file: " + ex.getMessage());
+                logger.error("Unable to read ROM file: {}", ex.getMessage());
                 JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             } catch (MemoryRangeException ex) {
-                logger.log(Level.SEVERE, "Memory range error while loading ROM file: " + ex.getMessage());
+                logger.error("Memory range error while loading ROM file: {}", ex.getMessage());
                 JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             } catch (MemoryAccessException ex) {
-                logger.log(Level.SEVERE, "Memory access error while loading ROM file: " + ex.getMessage());
+                logger.error("Memory access error while loading ROM file: {}", ex.getMessage());
                 JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             }
         }
@@ -616,7 +616,7 @@ public class Simulator {
             }
             mainWindow.dispose();
 
-            command = MAIN_CMD.SELECTMACHINE;
+            command = MainCommand.SELECTMACHINE;
             synchronized (commandMonitorObject) {
                 commandMonitorObject.notifyAll();
             }
@@ -645,11 +645,12 @@ public class Simulator {
         public SetFontAction(int size) {
             super(Integer.toString(size) + " pt", null);
             this.size = size;
-            putValue(SHORT_DESCRIPTION, "Set font to " + Integer.toString(size) + "pt.");
+            putValue(SHORT_DESCRIPTION, "Set font to " + size + "pt.");
         }
 
         public void actionPerformed(ActionEvent actionEvent) {
             SwingUtilities.invokeLater(new Runnable() {
+                @Override
                 public void run() {
                     console.setFont(new Font("Monospaced", Font.PLAIN, size));
                     mainWindow.pack();
@@ -658,6 +659,25 @@ public class Simulator {
         }
     }
 
+    class SetSpeedAction extends AbstractAction {
+        private int speed;
+
+        public SetSpeedAction(int speed) {
+            super(Integer.toString(speed) + " MHz", null);
+            this.speed = speed;
+            putValue(SHORT_DESCRIPTION, "Set simulated speed to " + speed + " MHz.");
+        }
+
+        @Override
+        public void actionPerformed(ActionEvent actionEvent) {
+            if (speed < 1 || speed > CLOCK_PERIODS.length - 1) {
+                return;
+            }
+
+            machine.getCpu().setClockPeriodInNs(CLOCK_PERIODS[speed]);
+        }
+    }
+
     class ToggleTraceWindowAction extends AbstractAction {
         public ToggleTraceWindowAction() {
             super("Trace Log", null);
@@ -710,6 +730,23 @@ public class Simulator {
         }
     }
 
+    class ToggleBreakpointWindowAction extends AbstractAction {
+        public ToggleBreakpointWindowAction() {
+            super("Breakpoints...", null);
+            putValue(SHORT_DESCRIPTION, "Show or Hide Breakpoints");
+        }
+
+        public void actionPerformed(ActionEvent actionEvent) {
+            synchronized (breakpointsWindow) {
+                if (breakpointsWindow.isVisible()) {
+                    breakpointsWindow.setVisible(false);
+                } else {
+                    breakpointsWindow.setVisible(true);
+                }
+            }
+        }
+    }
+
     class SimulatorMenu extends JMenuBar {
         // Menu Items
         private JMenuItem loadProgramItem;
@@ -762,9 +799,6 @@ public class Simulator {
             JMenuItem prefsItem = new JMenuItem(new ShowPrefsAction());
             fileMenu.add(prefsItem);
 
-            JMenuItem selectMachineItem = new JMenuItem(new SelectMachineAction());
-            fileMenu.add(selectMachineItem);
-
             JMenuItem quitItem = new JMenuItem(new QuitAction());
             fileMenu.add(quitItem);
 
@@ -822,16 +856,79 @@ public class Simulator {
             }
 
             add(viewMenu);
+
+            /*
+             * Simulator Menu
+             */
+
+
+            JMenu simulatorMenu = new JMenu("Simulator");
+
+            // "Select Machine..." item.
+            JMenuItem selectMachineItem = new JMenuItem(new SelectMachineAction());
+            simulatorMenu.add(selectMachineItem);
+
+            // "Clock Speed" sub-menu
+            JMenu speedSubMenu = new JMenu("Clock Speed");
+            ButtonGroup speedGroup = new ButtonGroup();
+
+            makeSpeedMenuItem(1, speedSubMenu, speedGroup);
+            makeSpeedMenuItem(2, speedSubMenu, speedGroup);
+            makeSpeedMenuItem(4, speedSubMenu, speedGroup);
+            makeSpeedMenuItem(8, speedSubMenu, speedGroup);
+
+            simulatorMenu.add(speedSubMenu);
+
+            // "Breakpoints"
+            final JCheckBoxMenuItem showBreakpoints = new JCheckBoxMenuItem(new ToggleBreakpointWindowAction());
+            // Un-check the menu item if the user closes the window directly
+            breakpointsWindow.addWindowListener(new WindowAdapter() {
+                @Override
+                public void windowClosing(WindowEvent e) {
+                    showBreakpoints.setSelected(false);
+                }
+            });
+            simulatorMenu.add(showBreakpoints);
+
+            add(simulatorMenu);
         }
 
-        private void makeFontSizeMenuItem(int size, JMenu fontSubMenu, ButtonGroup group) {
+        private void makeFontSizeMenuItem(int size, JMenu subMenu, ButtonGroup group) {
             Action action = new SetFontAction(size);
 
             JCheckBoxMenuItem item = new JCheckBoxMenuItem(action);
             item.setSelected(size == DEFAULT_FONT_SIZE);
-            fontSubMenu.add(item);
+            subMenu.add(item);
+            group.add(item);
+        }
+
+        private void makeSpeedMenuItem(int speed, JMenu subMenu, ButtonGroup group) {
+            if (speed < 1 || speed > CLOCK_PERIODS.length - 1) {
+                return;
+            }
+
+            Action action = new SetSpeedAction(speed);
+
+            JCheckBoxMenuItem item = new JCheckBoxMenuItem(action);
+            item.setSelected(CLOCK_PERIODS[speed] == Cpu.DEFAULT_CLOCK_PERIOD_IN_NS);
+            subMenu.add(item);
             group.add(item);
         }
     }
 
+    private void updateVisibleState() {
+        // Immediately update the UI.
+        SwingUtilities.invokeLater(new Runnable() {
+            @Override
+            public void run() {
+                // Now update the state
+                statusPane.updateState();
+                memoryWindow.updateState();
+                if (traceLog.shouldUpdate()) {
+                    traceLog.refresh();
+                }
+            }
+        });
+    }
+
 }

src/main/java/com/loomcom/symon/devices/Acia.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -82,6 +82,7 @@ public abstract class Acia extends Device {
     /**
      * @return The simulated baud rate in bps.
      */
+    @SuppressWarnings("unused")
     public int getBaudRate() {
         return baudRate;
     }
@@ -153,6 +154,7 @@ public abstract class Acia extends Device {
     /**
      * @return true if there is character data in the RX register.
      */
+    @SuppressWarnings("unused")
     public boolean hasRxChar() {
         return rxFull;
     }

src/main/java/com/loomcom/symon/devices/Acia6551.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -26,7 +26,6 @@ package com.loomcom.symon.devices;
 import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
-
 /**
  * This is a simulation of the MOS 6551 ACIA, with limited
  * functionality.  Interrupts are not supported.
@@ -45,7 +44,6 @@ public class Acia6551 extends Acia {
     static final int CMND_REG = 2;
     static final int CTRL_REG = 3;
 
-
     /**
      * Registers. These are ignored in the current implementation.
      */
@@ -106,7 +104,7 @@ public class Acia6551 extends Acia {
     /**
      * Set the control register and associated state.
      *
-     * @param data
+     * @param data Data to write into the control register
      */
     private void setControlRegister(int data) {
         controlRegister = data;

src/main/java/com/loomcom/symon/devices/Acia6850.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *                    Maik Merten <maikmerten@googlemail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -41,20 +41,12 @@ public class Acia6850 extends Acia {
 
     public static final int ACIA_SIZE = 2;
 
-
     static final int STAT_REG = 0;	// read-only
     static final int CTRL_REG = 0;	// write-only
 	
     static final int RX_REG = 1;	// read-only
     static final int TX_REG = 1;	// write-only
 
-    
-    /**
-     * Registers. These are ignored in the current implementation.
-     */
-    private int commandRegister;
-
-
     public Acia6850(int address) throws MemoryRangeException {
         super(address, ACIA_SIZE, "ACIA6850");
         setBaudRate(2400);
@@ -88,17 +80,15 @@ public class Acia6850 extends Acia {
     }
     
     private void setCommandRegister(int data) {
-        commandRegister = data;
-		
         // Bits 0 & 1 control the master reset
-        if((commandRegister & 0x01) != 0 && (commandRegister & 0x02) != 0) {
+        if((data & 0x01) != 0 && (data & 0x02) != 0) {
             reset();
         }
 
         // Bit 7 controls receiver IRQ behavior
-        receiveIrqEnabled = (commandRegister & 0x80) != 0;
+        receiveIrqEnabled = (data & 0x80) != 0;
         // Bits 5 & 6 controls transmit IRQ behavior
-        transmitIrqEnabled = (commandRegister & 0x20) != 0 && (commandRegister & 0x40) == 0;
+        transmitIrqEnabled = (data & 0x20) != 0 && (data & 0x40) == 0;
     }
 
 

src/main/java/com/loomcom/symon/devices/Crtc.java

@@ -1,20 +1,37 @@
+/*
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
 package com.loomcom.symon.devices;
 
 import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
 import java.io.IOException;
-import java.util.logging.Logger;
-
 
 /**
  * Simulation of a 6545 CRTC and virtual CRT output.
  */
 public class Crtc extends Device {
-
-    private static final Logger logger = Logger.getLogger(Crtc.class.getName());
-
-
     // Memory locations in the CRTC address space
     public static final int REGISTER_SELECT          = 0;
     public static final int REGISTER_RW              = 1;
@@ -65,6 +82,11 @@ public class Crtc extends Device {
 
     private int currentRegister = 0;
 
+    // Status bits
+    private boolean rowColumnAddressing = false;
+    private boolean displayEnableSkew = false;
+    private boolean cursorSkew = false;
+
     private Memory memory;
 
     public Crtc(int deviceAddress, Memory memory) throws MemoryRangeException, IOException {
@@ -118,8 +140,9 @@ public class Crtc extends Device {
         return null;
     }
 
-    public int[] getDmaAccess() {
+    public int getCharAtAddress(int address) throws MemoryAccessException {
-        return memory.getDmaAccess();
+        // TODO: Row/Column addressing
+        return memory.read(address);
     }
 
     public int getHorizontalDisplayed() {
@@ -162,6 +185,18 @@ public class Crtc extends Device {
         return pageSize;
     }
 
+    public boolean getRowColumnAddressing() {
+        return rowColumnAddressing;
+    }
+
+    public boolean getDisplayEnableSkew() {
+        return displayEnableSkew;
+    }
+
+    public boolean getCursorSkew() {
+        return cursorSkew;
+    }
+
     private void setCurrentRegister(int registerNumber) {
         this.currentRegister = registerNumber;
     }
@@ -180,7 +215,9 @@ public class Crtc extends Device {
                 pageSize = horizontalDisplayed * verticalDisplayed;
                 break;
             case MODE_CONTROL:
-                // TODO: Implement multiple addressing modes and cursor skew.
+                rowColumnAddressing = (data & 0x04) != 0;
+                displayEnableSkew = (data & 0x10) != 0;
+                cursorSkew = (data & 0x20) != 0;
                 break;
             case SCAN_LINE:
                 scanLinesPerRow = data;

src/main/java/com/loomcom/symon/devices/Device.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -62,16 +62,11 @@ public abstract class Device implements Comparable<Device> {
      */
     private Set<DeviceChangeListener> deviceChangeListeners;
 
-    public Device(int startAddress, int endAddress, String name)
+    public Device(int startAddress, int endAddress, String name) throws MemoryRangeException {
-            throws MemoryRangeException {
         this.memoryRange = new MemoryRange(startAddress, endAddress);
         this.size = endAddress - startAddress + 1;
         this.name = name;
-        this.deviceChangeListeners = new HashSet<DeviceChangeListener>();
+        this.deviceChangeListeners = new HashSet<>();
-    }
-
-    public Device(int startAddress, int endAddress) throws MemoryRangeException {
-        this(startAddress, endAddress, null);
     }
 
     /* Methods required to be implemented by inheriting classes. */
@@ -97,6 +92,7 @@ public abstract class Device implements Comparable<Device> {
         return memoryRange.endAddress();
     }
 
+    @SuppressWarnings("unused")
     public int startAddress() {
         return memoryRange.startAddress();
     }
@@ -105,6 +101,7 @@ public abstract class Device implements Comparable<Device> {
         return name;
     }
 
+    @SuppressWarnings("unused")
     public void setName(String name) {
         this.name = name;
     }
@@ -118,8 +115,8 @@ public abstract class Device implements Comparable<Device> {
     }
 
     public void notifyListeners() {
-        for (DeviceChangeListener l : deviceChangeListeners) {
+        for (DeviceChangeListener listener : deviceChangeListeners) {
-            l.deviceStateChanged();
+            listener.deviceStateChanged();
         }
     }
 

src/main/java/com/loomcom/symon/devices/DeviceChangeListener.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -24,5 +24,5 @@
 package com.loomcom.symon.devices;
 
 public interface DeviceChangeListener {
-    public void deviceStateChanged();
+    void deviceStateChanged();
 }

src/main/java/com/loomcom/symon/devices/Memory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -28,8 +28,6 @@ import java.util.*;
 
 import com.loomcom.symon.exceptions.*;
 
-import javax.swing.*;
-
 public class Memory extends Device {
 
     private boolean readOnly;
@@ -57,8 +55,7 @@ public class Memory extends Device {
     }
 
     public static Memory makeRAM(int startAddress, int endAddress) throws MemoryRangeException {
-        Memory memory = new Memory(startAddress, endAddress, false);
+        return new Memory(startAddress, endAddress, false);
-        return memory;
     }
 
     public void write(int address, int data) throws MemoryAccessException {
@@ -108,8 +105,4 @@ public class Memory extends Device {
     public String toString() {
         return "Memory: " + getMemoryRange().toString();
     }
-
-    public int[] getDmaAccess() {
-        return mem;
-    }
 }

src/main/java/com/loomcom/symon/devices/Pia.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,45 +23,19 @@
 
 package com.loomcom.symon.devices;
 
-import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
-public class Via extends Device {
+public abstract class Pia extends Device {
-    public static final int VIA_SIZE = 16;
 
-    private static final int ORB = 0;
+    private final String name;
-    private static final int ORA = 1;
-    private static final int DDRB = 2;
-    private static final int DDRA = 3;
-    private static final int T1C_L = 4;
-    private static final int T1C_H = 5;
-    private static final int T1L_L = 6;
-    private static final int T1L_H = 7;
-    private static final int T2C_L = 8;
-    private static final int T2C_H = 9;
-    private static final int SR = 10;
-    private static final int ACR = 11;
-    private static final int PCR = 12;
-    private static final int IFR = 13;
-    private static final int IER = 14;
-    private static final int ORA_H = 15;
 
-    public Via(int address) throws MemoryRangeException {
+    public Pia(int startAddress, int endAddress, String name) throws MemoryRangeException {
-      super(address, address + VIA_SIZE - 1, "VIA");
+        super(startAddress, endAddress, name);
-    }
+        this.name = name;
-
-    @Override
-    public void write(int address, int data) throws MemoryAccessException {
-
-    }
-
-    @Override
-    public int read(int address) throws MemoryAccessException {
-        return 0;
     }
 
     @Override
     public String toString() {
-        return null;
+        return name;
     }
 }

src/main/java/com/loomcom/symon/devices/SdController.java

@@ -0,0 +1,210 @@
+/*
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ *                    Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Emulation for the SD-card controller of the MULTICOMP system.
+ * Neiter comlete nor correct.
+ */
+public class SdController extends Device {
+
+    private enum Status {
+        IDLE,
+        READ,
+        WRITE
+    }
+
+    public static final int CONTROLLER_SIZE = 8;
+    private final int SECTOR_SIZE = 512;
+    private final static Logger logger = Logger.getLogger(SdController.class.getName());
+
+    private File sdImageFile;
+    private int lba0, lba1, lba2;
+    private int position;
+    private Status status = Status.IDLE;
+
+    private final byte[] readBuffer = new byte[SECTOR_SIZE];
+    private final byte[] writeBuffer = new byte[SECTOR_SIZE];
+    private int readPosition = 0;
+    private int writePosition = 0;
+
+
+    public SdController(int address) throws MemoryRangeException {
+        super(address, address + CONTROLLER_SIZE - 1, "SDCONTROLLER");
+
+        sdImageFile = new File("sd.img");
+        if (!sdImageFile.exists()) {
+            sdImageFile = null;
+            logger.log(Level.INFO, "Could not find SD card image 'sd.img'");
+        }
+    }
+
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        switch (address) {
+            case 0:
+                writeData(data);
+                return;
+            case 1:
+                writeCommand(data);
+                return;
+            case 2:
+                this.lba0 = data;
+                return;
+            case 3:
+                this.lba1 = data;
+                return;
+            case 4:
+                this.lba2 = data;
+        }
+    }
+
+    @Override
+    public int read(int address) throws MemoryAccessException {
+        switch (address) {
+            case 0:
+                return readData();
+            case 1:
+                return readStatus();
+            default:
+                return 0;
+        }
+    }
+
+    private void computePosition() {
+        this.position = lba0 + (lba1 << 8) + (lba2 << 16);
+        // each sector is 512 bytes, so multiply accordingly
+        this.position <<= 9;
+    }
+
+    private void prepareRead() {
+        this.status = Status.READ;
+        this.readPosition = 0;
+        computePosition();
+
+        if (sdImageFile != null) {
+            try {
+                FileInputStream fis = new FileInputStream(sdImageFile);
+                fis.skip(this.position);
+                int read = fis.read(readBuffer);
+                if (read < SECTOR_SIZE) {
+                    logger.log(Level.WARNING, "not enough data to fill read buffer from SD image file");
+                }
+                fis.close();
+            } catch (IOException ex) {
+                logger.log(Level.WARNING, "could not fill read buffer from SD image file", ex);
+            }
+        }
+    }
+
+    private void prepareWrite() {
+        this.status = Status.WRITE;
+        this.writePosition = 0;
+        computePosition();
+    }
+
+
+    private int readData() {
+        if (status != Status.READ) {
+            return 0;
+        }
+
+        int data = readBuffer[readPosition++];
+
+        if (readPosition >= SECTOR_SIZE) {
+            this.status = Status.IDLE;
+        }
+
+        return data;
+    }
+
+    private void writeData(int data) {
+        if (status != Status.WRITE) {
+            return;
+        }
+
+        writeBuffer[writePosition++] = (byte) data;
+
+        if (writePosition >= SECTOR_SIZE) {
+            if (sdImageFile != null) {
+                try {
+                    RandomAccessFile raf = new RandomAccessFile(sdImageFile, "rw");
+                    raf.skipBytes(this.position);
+                    raf.write(writeBuffer, 0, writeBuffer.length);
+                    raf.close();
+                } catch (IOException ex) {
+                    logger.log(Level.WARNING, "could not write data back to SD image file!", ex);
+                }
+            }
+
+            this.status = Status.IDLE;
+        }
+
+    }
+
+    private int readStatus() {
+        switch (this.status) {
+            case IDLE:
+                return 128;
+            case READ:
+                return 224;
+            case WRITE:
+                return 160;
+            default:
+                return 0;
+        }
+    }
+
+    private void writeCommand(int data) {
+        switch (data) {
+            case 0:
+                prepareRead();
+                return;
+            case 1:
+                prepareWrite();
+                return;
+            default:
+                this.status = Status.IDLE;
+        }
+    }
+
+    @Override
+    public String toString() {
+        return getName() + "@" + String.format("%04X", this.getMemoryRange().startAddress);
+    }
+
+}

src/main/java/com/loomcom/symon/devices/Via6522.java

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.devices;
+
+import com.loomcom.symon.exceptions.MemoryAccessException;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+/**
+ * Very basic implementation of a MOS 6522 VIA.
+ *
+ * TODO: Implement timers as threads.
+ */
+public class Via6522 extends Pia {
+    public static final int VIA_SIZE = 16;
+
+    enum Register {
+        ORB, ORA, DDRB, DDRA, T1C_L, T1C_H, T1L_L, T1L_H,
+        T2C_L, T2C_H, SR, ACR, PCR, IFR, IER, ORA_H
+    }
+
+    public Via6522(int address) throws MemoryRangeException {
+        super(address, address + VIA_SIZE - 1, "MOS 6522 VIA");
+    }
+
+    @Override
+    public void write(int address, int data) throws MemoryAccessException {
+        Register[] registers = Register.values();
+
+        if (address >= registers.length) {
+            throw new MemoryAccessException("Unknown register: " + address);
+        }
+
+        Register r = registers[address];
+
+        switch (r) {
+            case ORA:
+            case ORB:
+            case DDRA:
+            case DDRB:
+            case T1C_L:
+            case T1C_H:
+            case T1L_L:
+            case T1L_H:
+            case T2C_L:
+            case T2C_H:
+            case SR:
+            case ACR:
+            case PCR:
+            case IFR:
+            case IER:
+            case ORA_H:
+            default:
+        }
+    }
+
+    @Override
+    public int read(int address) throws MemoryAccessException {
+        Register[] registers = Register.values();
+
+        if (address >= registers.length) {
+            throw new MemoryAccessException("Unknown register: " + address);
+        }
+
+        Register r = registers[address];
+
+        switch (r) {
+            case ORA:
+            case ORB:
+            case DDRA:
+            case DDRB:
+            case T1C_L:
+            case T1C_H:
+            case T1L_L:
+            case T1L_H:
+            case T2C_L:
+            case T2C_H:
+            case SR:
+            case ACR:
+            case PCR:
+            case IFR:
+            case IER:
+            case ORA_H:
+            default:
+        }
+
+        return 0;
+    }
+}

src/main/java/com/loomcom/symon/exceptions/FifoUnderrunException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the

src/main/java/com/loomcom/symon/exceptions/MemoryAccessException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the

src/main/java/com/loomcom/symon/exceptions/MemoryRangeException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the

src/main/java/com/loomcom/symon/exceptions/SymonException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -31,7 +31,4 @@ public class SymonException extends Exception {
     public SymonException(String msg) {
         super(msg);
     }
-    public SymonException() {
-        super();
-    }
 }

src/main/java/com/loomcom/symon/machines/Machine.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2014 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *                    Maik Merten <maikmerten@googlemail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -29,33 +29,33 @@ import com.loomcom.symon.Cpu;
 import com.loomcom.symon.devices.Acia;
 import com.loomcom.symon.devices.Crtc;
 import com.loomcom.symon.devices.Memory;
-import com.loomcom.symon.devices.Via;
+import com.loomcom.symon.devices.Pia;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
 
 public interface Machine {
     
-    public Bus getBus();
+    Bus getBus();
 
-    public Cpu getCpu();
+    Cpu getCpu();
     
-    public Memory getRam();
+    Memory getRam();
     
-    public Acia getAcia();
+    Acia getAcia();
     
-    public Via getVia();
+    Pia getPia();
     
-    public Crtc getCrtc();
+    Crtc getCrtc();
     
-    public Memory getRom();
+    Memory getRom();
     
-    public void setRom(Memory rom) throws MemoryRangeException;
+    void setRom(Memory rom) throws MemoryRangeException;
     
-    public int getRomBase();
+    int getRomBase();
     
-    public int getRomSize();
+    int getRomSize();
     
-    public int getMemorySize();
+    int getMemorySize();
 
     String getName();
 }

src/main/java/com/loomcom/symon/machines/MulticompMachine.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2014 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *                    Maik Merten <maikmerten@googlemail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -30,7 +30,8 @@ import com.loomcom.symon.devices.Acia;
 import com.loomcom.symon.devices.Acia6850;
 import com.loomcom.symon.devices.Crtc;
 import com.loomcom.symon.devices.Memory;
-import com.loomcom.symon.devices.Via;
+import com.loomcom.symon.devices.Pia;
+import com.loomcom.symon.devices.SdController;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 import java.io.File;
 import java.util.logging.Logger;
@@ -51,6 +52,8 @@ public class MulticompMachine implements Machine {
     // ACIA at $FFD0-$FFD1
     private static final int ACIA_BASE = 0xFFD0;
 
+    // SD controller at $FFD8-$FFDF
+    private static final int SD_BASE = 0xFFD8;
 
     // 8KB ROM at $E000-$FFFF
     private static final int ROM_BASE = 0xE000;
@@ -70,10 +73,12 @@ public class MulticompMachine implements Machine {
         this.cpu = new Cpu();
         this.ram = new Memory(MEMORY_BASE, MEMORY_BASE + MEMORY_SIZE - 1, false);
         this.acia = new Acia6850(ACIA_BASE);
+        this.acia.setBaudRate(0);
 
         bus.addCpu(cpu);
         bus.addDevice(ram);
         bus.addDevice(acia, 1);
+        bus.addDevice(new SdController(SD_BASE), 1);
         
         // TODO: Make this configurable, of course.
         File romImage = new File("rom.bin");
@@ -111,7 +116,7 @@ public class MulticompMachine implements Machine {
     }
 
     @Override
-    public Via getVia() {
+    public Pia getPia() {
         return null;
     }
 

src/main/java/com/loomcom/symon/machines/SimpleMachine.java

@@ -1,3 +1,27 @@
+/*
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ *                    Maik Merten <maikmerten@googlemail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
 package com.loomcom.symon.machines;
 
 import com.loomcom.symon.Bus;
@@ -5,7 +29,7 @@ import com.loomcom.symon.Cpu;
 import com.loomcom.symon.devices.Acia;
 import com.loomcom.symon.devices.Crtc;
 import com.loomcom.symon.devices.Memory;
-import com.loomcom.symon.devices.Via;
+import com.loomcom.symon.devices.Pia;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
 /**
@@ -52,7 +76,7 @@ public class SimpleMachine implements Machine {
     }
 
     @Override
-    public Via getVia() {
+    public Pia getPia() {
         return null;
     }
 

src/main/java/com/loomcom/symon/machines/SymonMachine.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2014 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *                    Maik Merten <maikmerten@googlemail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -26,19 +26,16 @@ package com.loomcom.symon.machines;
 
 import com.loomcom.symon.Bus;
 import com.loomcom.symon.Cpu;
-import com.loomcom.symon.devices.Acia;
+import com.loomcom.symon.devices.*;
-import com.loomcom.symon.devices.Acia6551;
-import com.loomcom.symon.devices.Crtc;
-import com.loomcom.symon.devices.Memory;
-import com.loomcom.symon.devices.Via;
 import com.loomcom.symon.exceptions.MemoryRangeException;
-import java.io.File;
+import org.slf4j.Logger;
-import java.util.logging.Logger;
+import org.slf4j.LoggerFactory;
 
+import java.io.File;
 
 public class SymonMachine implements Machine {
     
-    private final static Logger logger = Logger.getLogger(SymonMachine.class.getName());
+    private final static Logger logger = LoggerFactory.getLogger(SymonMachine.class.getName());
     
     // Constants used by the simulated system. These define the memory map.
     private static final int BUS_BOTTOM = 0x0000;
@@ -48,16 +45,15 @@ public class SymonMachine implements Machine {
     private static final int MEMORY_BASE = 0x0000;
     private static final int MEMORY_SIZE = 0x8000;
 
-    // VIA at $8000-$800F
+    // PIA at $8000-$800F
 
-    private static final int VIA_BASE = 0x8000;
+    private static final int PIA_BASE = 0x8000;
 
     // ACIA at $8800-$8803
     private static final int ACIA_BASE = 0x8800;
 
     // CRTC at $9000-$9001
     private static final int CRTC_BASE = 0x9000;
-    private static final int VIDEO_RAM_BASE = 0x7000;
 
     // 16KB ROM at $C000-$FFFF
     private static final int ROM_BASE = 0xC000;
@@ -68,7 +64,7 @@ public class SymonMachine implements Machine {
     private final Bus    bus;
     private final Cpu    cpu;
     private final Acia   acia;
-    private final Via    via;
+    private final Pia    pia;
     private final Crtc   crtc;
     private final Memory ram;
     private       Memory rom;
@@ -78,24 +74,23 @@ public class SymonMachine implements Machine {
         this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
         this.cpu = new Cpu();
         this.ram = new Memory(MEMORY_BASE, MEMORY_BASE + MEMORY_SIZE - 1, false);
-        this.via = new Via(VIA_BASE);
+        this.pia = new Via6522(PIA_BASE);
         this.acia = new Acia6551(ACIA_BASE);
         this.crtc = new Crtc(CRTC_BASE, ram);
 
         bus.addCpu(cpu);
         bus.addDevice(ram);
-        bus.addDevice(via);
+        bus.addDevice(pia);
         bus.addDevice(acia);
         bus.addDevice(crtc);
         
         // TODO: Make this configurable, of course.
         File romImage = new File("rom.bin");
         if (romImage.canRead()) {
-            logger.info("Loading ROM image from file " + romImage);
+            logger.info("Loading ROM image from file {}", romImage);
             this.rom = Memory.makeROM(ROM_BASE, ROM_BASE + ROM_SIZE - 1, romImage);
         } else {
-            logger.info("Default ROM file " + romImage +
+            logger.info("Default ROM file {} not found, loading empty R/W memory image.", romImage);
-                        " not found, loading empty R/W memory image.");
             this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
         }
 
@@ -124,8 +119,8 @@ public class SymonMachine implements Machine {
     }
 
     @Override
-    public Via getVia() {
+    public Pia getPia() {
-        return via;
+        return pia;
     }
 
     @Override

src/main/java/com/loomcom/symon/ui/BreakpointsWindow.java

@@ -0,0 +1,152 @@
+/*
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package com.loomcom.symon.ui;
+
+import com.loomcom.symon.Breakpoints;
+import com.loomcom.symon.util.Utils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.swing.*;
+import javax.swing.border.EmptyBorder;
+import javax.swing.event.ListSelectionEvent;
+import javax.swing.event.ListSelectionListener;
+import java.awt.*;
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
+
+/**
+ * Simple window to enter breakpoints.
+ */
+public class BreakpointsWindow extends JFrame {
+
+    private static final Logger logger = LoggerFactory.getLogger(BreakpointsWindow.class);
+
+    private static final Dimension FRAME_SIZE = new Dimension(240, 280);
+    private static final String EMPTY_STRING = "";
+
+    private JFrame mainWindow;
+    private Breakpoints breakpoints;
+
+    public BreakpointsWindow(Breakpoints breakpoints,
+                             JFrame mainWindow) {
+        this.breakpoints = breakpoints;
+        this.mainWindow = mainWindow;
+        createUi();
+    }
+
+    private void createUi() {
+        setTitle("Breakpoints");
+
+        JPanel breakpointsPanel = new JPanel();
+        JPanel controlPanel = new JPanel();
+
+        breakpointsPanel.setLayout(new BorderLayout());
+        breakpointsPanel.setBorder(new EmptyBorder(10, 10, 10, 10));
+
+        final JButton addButton = new JButton("Add");
+        final JButton removeButton = new JButton("Del");
+        removeButton.setEnabled(false);
+
+        final JTextField addTextField = new JTextField(4);
+
+        final JTable breakpointsTable = new JTable(breakpoints);
+        breakpointsTable.setShowGrid(true);
+        breakpointsTable.setGridColor(Color.LIGHT_GRAY);
+        breakpointsTable.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
+        breakpointsTable.getSelectionModel().addListSelectionListener(new ListSelectionListener() {
+            @Override
+            public void valueChanged(ListSelectionEvent e) {
+                if (e.getFirstIndex() > -1) {
+                    removeButton.setEnabled(true);
+                } else {
+                    removeButton.setEnabled(false);
+                }
+            }
+        });
+
+        JScrollPane scrollPane = new JScrollPane(breakpointsTable);
+        scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
+        scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
+
+        breakpointsPanel.add(scrollPane, BorderLayout.CENTER);
+
+        ActionListener addBreakpointListener = new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                int value;
+
+                String newBreakpoint = addTextField.getText();
+
+                if (newBreakpoint == null || newBreakpoint.isEmpty()) {
+                    return;
+                }
+
+                try {
+                    value = (Integer.parseInt(addTextField.getText(), 16) & 0xffff);
+                } catch (NumberFormatException ex) {
+                    logger.warn("Can't parse page number {}", newBreakpoint);
+                    return;
+                }
+
+                if (value < 0) {
+                    return;
+                }
+
+                breakpoints.addBreakpoint(value);
+
+                logger.debug("Added breakpoint ${}", Utils.wordToHex(value));
+
+                addTextField.setText(EMPTY_STRING);
+            }
+        };
+
+        addButton.addActionListener(addBreakpointListener);
+        addTextField.addActionListener(addBreakpointListener);
+
+        removeButton.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                breakpoints.removeBreakpointAtIndex(breakpointsTable.getSelectedRow());
+            }
+        });
+
+        controlPanel.add(addTextField);
+        controlPanel.add(addButton);
+        controlPanel.add(removeButton);
+
+        setLayout(new BorderLayout());
+        getContentPane().add(breakpointsPanel, BorderLayout.CENTER);
+        getContentPane().add(controlPanel, BorderLayout.SOUTH);
+
+        setMinimumSize(FRAME_SIZE);
+        setMaximumSize(FRAME_SIZE);
+        setPreferredSize(FRAME_SIZE);
+
+        setLocationRelativeTo(mainWindow);
+        setResizable(false);
+
+        pack();
+    }
+}

src/main/java/com/loomcom/symon/ui/Console.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -44,21 +44,20 @@ import java.awt.event.MouseListener;
 
 public class Console extends JTerminal implements KeyListener, MouseListener {
 
-    private static final int     DEFAULT_COLUMNS      = 80;
-    private static final int     DEFAULT_ROWS         = 24;
     private static final int     DEFAULT_BORDER_WIDTH = 10;
     // If true, swap CR and LF characters.
     private static final boolean SWAP_CR_AND_LF       = true;
-    // If true, send CRLF (0x0d 0x0a) whenever CR is typed
-    private static final boolean SEND_CR_LF_FOR_CR    = false;
 
+    // If true, send CRLF (0x0d 0x0a) whenever CR is typed
+    private boolean sendCrForLf = false;
     private FifoRingBuffer<Character> typeAheadBuffer;
 
-    public Console(int columns, int rows, Font font) {
+    public Console(int columns, int rows, Font font, boolean sendCrForLf) {
         super(new Vt100TerminalModel(columns, rows), font);
         // A small type-ahead buffer, as might be found in any real
         // VT100-style serial terminal.
-        this.typeAheadBuffer = new FifoRingBuffer<Character>(128);
+        this.typeAheadBuffer = new FifoRingBuffer<>(128);
+        this.sendCrForLf = sendCrForLf;
         setBorderWidth(DEFAULT_BORDER_WIDTH);
         addKeyListener(this);
         addMouseListener(this);
@@ -83,7 +82,7 @@ public class Console extends JTerminal implements KeyListener, MouseListener {
     /**
      * Returns true if a key has been pressed since the last time input was read.
      *
-     * @return
+     * @return true if the type-ahead buffer has data
      */
     public boolean hasInput() {
         return !typeAheadBuffer.isEmpty();
@@ -105,7 +104,7 @@ public class Console extends JTerminal implements KeyListener, MouseListener {
             }
         }
 
-        if (SEND_CR_LF_FOR_CR && keyTyped == 0x0d) {
+        if (sendCrForLf && keyTyped == 0x0d) {
             typeAheadBuffer.push((char) 0x0d);
             typeAheadBuffer.push((char) 0x0a);
         } else {

src/main/java/com/loomcom/symon/ui/MemoryWindow.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -25,7 +25,9 @@ package com.loomcom.symon.ui;
 
 import com.loomcom.symon.Bus;
 import com.loomcom.symon.exceptions.MemoryAccessException;
-import com.loomcom.symon.util.HexUtil;
+import com.loomcom.symon.util.Utils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import javax.swing.*;
 import javax.swing.border.EmptyBorder;
@@ -37,8 +39,7 @@ import java.awt.*;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.util.EventObject;
-import java.util.logging.Level;
+
-import java.util.logging.Logger;
 
 /**
  * This Frame displays the contents of a page of memory. The page number to be displayed
@@ -46,6 +47,8 @@ import java.util.logging.Logger;
  */
 public class MemoryWindow extends JFrame implements ActionListener {
 
+    private static final Logger logger = LoggerFactory.getLogger(MemoryWindow.class);
+
     private MemoryTableModel memoryTableModel;
     private JTable memoryTable;
     private JTextField pageNumberTextField;
@@ -104,7 +107,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
 
         previousPageButton.setEnabled(pageNumber > 0x00);
         nextPageButton.setEnabled(pageNumber < 0xff);
-        pageNumberTextField.setText(HexUtil.byteToHex(pageNumber));
+        pageNumberTextField.setText(Utils.byteToHex(pageNumber));
     }
 
     /**
@@ -209,9 +212,9 @@ public class MemoryWindow extends JFrame implements ActionListener {
             } catch (NumberFormatException ex) {
                 // An invalid number was entered. Log the error, but otherwise
                 // take no action.
-                Logger.getLogger(this.getClass().getName()).log(Level.WARNING, "Can't parse page number " +
+                logger.warn("Can't parse page number {}", pageNumberInput);
-                        pageNumberInput);
             }
+
             updateControls();
         }
     }
@@ -325,13 +328,13 @@ public class MemoryWindow extends JFrame implements ActionListener {
         public Object getValueAt(int row, int column) {
             try {
                 if (column == 0) {
-                    return HexUtil.wordToHex(fullAddress(row, 1));
+                    return Utils.wordToHex(fullAddress(row, 1));
                 } else if (column < 9) {
                     // Display hex value of the data
-                    return HexUtil.byteToHex(bus.read(fullAddress(row, column)));
+                    return Utils.byteToHex(bus.read(fullAddress(row, column)));
                 } else {
                     // Display the ASCII equivalent (if printable)
-                    return HexUtil.byteToAscii(bus.read(fullAddress(row, column - 8)));
+                    return Utils.byteToAscii(bus.read(fullAddress(row, column - 8)));
                 }
             } catch (MemoryAccessException ex) {
                 return "??";
@@ -346,12 +349,8 @@ public class MemoryWindow extends JFrame implements ActionListener {
                     int fullAddress = fullAddress(row, column);
                     int newValue = Integer.parseInt(hexValue, 16) & 0xff;
                     bus.write(fullAddress, newValue);
-                } catch (MemoryAccessException ex) {
+                } catch (MemoryAccessException | NumberFormatException | ClassCastException ex) {
-                    ;
+                    // Intentionally swallow exception
-                } catch (NumberFormatException ex) {
-                    ;
-                } catch (ClassCastException ex) {
-                    ;
                 }
                 fireTableCellUpdated(row, column);
             }

src/main/java/com/loomcom/symon/ui/PreferencesDialog.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -98,19 +98,21 @@ public class PreferencesDialog extends Observable implements Preferences {
         JButton cancelButton = new JButton("Cancel");
 
         cancelButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
-                updateUi();
+                PreferencesDialog.this.updateUi();
                 dialog.setVisible(false);
             }
         });
 
         applyButton.addActionListener(new ActionListener() {
+            @Override
             public void actionPerformed(ActionEvent actionEvent) {
                 haltOnBreak = haltOnBreakCheckBox.isSelected();
-                programLoadAddress = hexToInt(programLoadAddressField.getText());
+                programLoadAddress = PreferencesDialog.this.hexToInt(programLoadAddressField.getText());
-                updateUi();
+                PreferencesDialog.this.updateUi();
                 // TODO: Actually check to see if values have changed, don't assume.
-                setChanged();
+                PreferencesDialog.this.setChanged();
                 PreferencesDialog.this.notifyObservers();
                 dialog.setVisible(false);
             }

src/main/java/com/loomcom/symon/ui/StatusPanel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -24,6 +24,7 @@
 package com.loomcom.symon.ui;
 
 import com.loomcom.symon.Cpu;
+import com.loomcom.symon.CpuState;
 import com.loomcom.symon.machines.Machine;
 
 import javax.swing.*;
@@ -32,9 +33,6 @@ import javax.swing.border.EtchedBorder;
 import java.awt.*;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
-import java.util.logging.Level;
-import java.util.logging.Logger;
-import java.util.regex.Pattern;
 
 /**
  * UI component that displays the current state of the simulated CPU.
@@ -56,7 +54,6 @@ public class StatusPanel extends JPanel {
     private ImageIcon negativeOn;
     private ImageIcon negativeOff;
 
-    private JLabel statusFlagsLabel;
     private JLabel carryFlagLabel;
     private JLabel zeroFlagLabel;
     private JLabel irqDisableFlagLabel;
@@ -72,13 +69,6 @@ public class StatusPanel extends JPanel {
     private JTextField xField;
     private JTextField yField;
 
-    private JLabel opcodeLabel;
-    private JLabel pcLabel;
-    private JLabel spLabel;
-    private JLabel aLabel;
-    private JLabel xLabel;
-    private JLabel yLabel;
-
     private Machine machine;
 
     private static final int EMPTY_BORDER = 10;
@@ -153,13 +143,13 @@ public class StatusPanel extends JPanel {
         statusFlagsPanel.add(carryFlagLabel);
 
         // Create and add register and address labels
-        statusFlagsLabel = makeLabel("Flags");
+        JLabel statusFlagsLabel = makeLabel("Flags");
-        opcodeLabel = makeLabel("IR");
+        JLabel opcodeLabel = makeLabel("Next IR");
-        pcLabel = makeLabel("PC");
+        JLabel pcLabel = makeLabel("PC");
-        spLabel = makeLabel("SP");
+        JLabel spLabel = makeLabel("SP");
-        aLabel = makeLabel("A");
+        JLabel aLabel = makeLabel("A");
-        xLabel = makeLabel("X");
+        JLabel xLabel = makeLabel("X");
-        yLabel = makeLabel("Y");
+        JLabel yLabel = makeLabel("Y");
 
         statusFlagsLabel.setToolTipText("6502 Processor Status Flags");
         opcodeLabel.setToolTipText("Instruction Register");
@@ -178,13 +168,13 @@ public class StatusPanel extends JPanel {
             @Override
             public void actionPerformed(ActionEvent e) {
                 try {
-                    int newVal = getHexVal(pcField) & 0xffff;
+                    int newVal = StatusPanel.this.getHexVal(pcField) & 0xffff;
                     machine.getCpu().setProgramCounter(newVal);
                 } catch (Exception ex) {
                     // Swallow exception
                 }
 
-                updateState();
+                StatusPanel.this.updateState();
             }
         });
 
@@ -192,13 +182,13 @@ public class StatusPanel extends JPanel {
             @Override
             public void actionPerformed(ActionEvent e) {
                 try {
-                    int newVal = getHexVal(spField) & 0xff;
+                    int newVal = StatusPanel.this.getHexVal(spField) & 0xff;
                     machine.getCpu().setStackPointer(newVal);
                 } catch (Exception ex) {
                     // Swallow exception
                 }
 
-                updateState();
+                StatusPanel.this.updateState();
             }
         });
 
@@ -206,13 +196,13 @@ public class StatusPanel extends JPanel {
             @Override
             public void actionPerformed(ActionEvent e) {
                 try {
-                    int newVal = getHexVal(aField) & 0xff;
+                    int newVal = StatusPanel.this.getHexVal(aField) & 0xff;
                     machine.getCpu().setAccumulator(newVal);
                 } catch (Exception ex) {
                     // Swallow exception
                 }
 
-                updateState();
+                StatusPanel.this.updateState();
             }
         });
 
@@ -220,13 +210,13 @@ public class StatusPanel extends JPanel {
             @Override
             public void actionPerformed(ActionEvent e) {
                 try {
-                    int newVal = getHexVal(xField) & 0xff;
+                    int newVal = StatusPanel.this.getHexVal(xField) & 0xff;
                     machine.getCpu().setXRegister(newVal);
                 } catch (Exception ex) {
                     // Swallow exception
                 }
 
-                updateState();
+                StatusPanel.this.updateState();
             }
         });
 
@@ -234,13 +224,13 @@ public class StatusPanel extends JPanel {
             @Override
             public void actionPerformed(ActionEvent e) {
                 try {
-                    int newVal = getHexVal(yField) & 0xff;
+                    int newVal = StatusPanel.this.getHexVal(yField) & 0xff;
                     machine.getCpu().setYRegister(newVal);
                 } catch (Exception ex) {
                     // Swallow exception
                 }
 
-                updateState();
+                StatusPanel.this.updateState();
             }
         });
 
@@ -303,7 +293,7 @@ public class StatusPanel extends JPanel {
      */
     public void updateState() {
         Cpu cpu = machine.getCpu();
-        Cpu.CpuState cpuState = cpu.getCpuState();
+        CpuState cpuState = cpu.getCpuState();
 
         // Update the Processor Status Flag display
         int status = cpuState.getStatusFlag();
@@ -317,7 +307,9 @@ public class StatusPanel extends JPanel {
         negativeFlagLabel.setIcon(iconForFlag(status, 7));
 
         // Update the register and address displays
-        opcodeField.setText(cpu.getCpuState().disassembleOp());
+
+        // We always want to show the NEXT instruction that will be executed
+        opcodeField.setText(cpu.disassembleNextOp());
         pcField.setText(cpu.getProgramCounterStatus());
         spField.setText(cpu.getStackPointerStatus());
         aField.setText(cpu.getAccumulatorStatus());

src/main/java/com/loomcom/symon/ui/TraceLog.java

@@ -1,5 +1,6 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ *                    Maik Merten <maikmerten@googlemail.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -23,7 +24,7 @@
 
 package com.loomcom.symon.ui;
 
-import com.loomcom.symon.Cpu;
+import com.loomcom.symon.CpuState;
 import com.loomcom.symon.util.FifoRingBuffer;
 
 import javax.swing.*;
@@ -35,15 +36,15 @@ import java.awt.*;
  */
 public class TraceLog extends JFrame {
 
-    private FifoRingBuffer<Cpu.CpuState> traceLog;
+    private final FifoRingBuffer<CpuState> traceLog;
-    private JTextArea                    traceLogTextArea;
+    private final JTextArea                    traceLogTextArea;
 
     private static final Dimension MIN_SIZE       = new Dimension(320, 200);
     private static final Dimension PREFERRED_SIZE = new Dimension(640, 480);
     private static final int       MAX_LOG_LENGTH = 50000;
 
     public TraceLog() {
-        traceLog = new FifoRingBuffer<Cpu.CpuState>(MAX_LOG_LENGTH);
+        traceLog = new FifoRingBuffer<>(MAX_LOG_LENGTH);
         setMinimumSize(MIN_SIZE);
         setPreferredSize(PREFERRED_SIZE);
         setResizable(true);
@@ -67,11 +68,15 @@ public class TraceLog extends JFrame {
      * call.
      */
     public void refresh() {
-        synchronized (this) {
         StringBuilder logString = new StringBuilder();        
-            for (Cpu.CpuState state : traceLog) {
+        
+        synchronized(traceLog) {
+            for (CpuState state : traceLog) {
                 logString.append(state.toTraceEvent());
             }
+        }
+
+        synchronized(traceLogTextArea) {
             traceLogTextArea.setText(logString.toString());
         }
     }
@@ -80,8 +85,10 @@ public class TraceLog extends JFrame {
      * Reset the log area.
      */
     public void reset() {
-        synchronized (this) {
+        synchronized(traceLog) {
             traceLog.reset();
+        }
+        synchronized(traceLogTextArea) {
             traceLogTextArea.setText("");
             traceLogTextArea.setEnabled(true);
         }
@@ -92,9 +99,9 @@ public class TraceLog extends JFrame {
      *
      * @param state The CPU State to append.
      */
-    public void append(Cpu.CpuState state) {
+    public void append(CpuState state) {
-        synchronized(this) {
+        synchronized(traceLog) {
-            traceLog.push(new Cpu.CpuState(state));
+            traceLog.push(new CpuState(state));
         }
     }
 
@@ -106,4 +113,8 @@ public class TraceLog extends JFrame {
         traceLogTextArea.setEnabled(true);
     }
 
+    public boolean shouldUpdate() {
+        return isVisible() && traceLogTextArea.isEnabled();
+    }
+
 }

src/main/java/com/loomcom/symon/ui/VideoWindow.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2013 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -25,6 +25,7 @@ package com.loomcom.symon.ui;
 
 import com.loomcom.symon.devices.Crtc;
 import com.loomcom.symon.devices.DeviceChangeListener;
+import com.loomcom.symon.exceptions.MemoryAccessException;
 
 import javax.swing.*;
 import java.awt.*;
@@ -36,8 +37,11 @@ import java.util.concurrent.Executors;
 import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
+import java.util.logging.Level;
 import java.util.logging.Logger;
 
+import static java.lang.System.*;
+
 /**
  * VideoWindow represents a graphics framebuffer backed by a 6545 CRTC.
  * Each time the window's VideoPanel is repainted, the video memory is
@@ -65,7 +69,6 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
     private BufferedImage image;
     private int[] charRom;
-    private int[] videoRam;
 
     private int horizontalDisplayed;
     private int verticalDisplayed;
@@ -85,6 +88,7 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
     private class VideoPanel extends JPanel {
         @Override
         public void paintComponent(Graphics g) {
+            try {
                 for (int i = 0; i < crtc.getPageSize(); i++) {
                     int address = crtc.getStartAddress() + i;
                     int originX = (i % horizontalDisplayed) * CHAR_WIDTH;
@@ -96,6 +100,9 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
                     g2d.scale(scaleX, scaleY);
                 }
                 g2d.drawImage(image, 0, 0, null);
+            } catch (MemoryAccessException ex) {
+                logger.log(Level.SEVERE, "Memory Access Exception, can't paint video window! " + ex.getMessage());
+            }
         }
 
         @Override
@@ -116,10 +123,11 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
     private class CursorBlinker implements Runnable {
         public void run() {
             SwingUtilities.invokeLater(new Runnable() {
+                @Override
                 public void run() {
                     if (cursorBlinkRate > 0) {
                         hideCursor = !hideCursor;
-                        repaint();
+                        VideoWindow.this.repaint();
                     }
                 }
             });
@@ -131,8 +139,7 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
         this.scheduler = Executors.newSingleThreadScheduledExecutor();
         this.crtc = crtc;
-        this.charRom = loadCharRom("/pet.rom");
+        this.charRom = loadCharRom("/ascii.rom");
-        this.videoRam = crtc.getDmaAccess();
         this.scaleX = scaleX;
         this.scaleY = scaleY;
         this.shouldScale = (scaleX > 1 || scaleY > 1);
@@ -158,13 +165,6 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
     }
 
-    public void refreshDisplay() {
-        // TODO: Verify whether this is necessary. Does `repaint()' do anything if the window is not visible?
-        if (isVisible()) {
-            repaint();
-        }
-    }
-
     /**
      * Called by the CRTC on state change.
      */
@@ -239,15 +239,13 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
      * @param address The address of the character being requested.
      * @return An array of integers representing the pixel data.
      */
-    private int[] getGlyph(int address) {
+    private int[] getGlyph(int address) throws MemoryAccessException {
-        int chr = videoRam[address];
+        int chr = crtc.getCharAtAddress(address);
         int romOffset = (chr & 0xff) * (CHAR_HEIGHT * CHAR_WIDTH);
         int[] glyph = new int[CHAR_WIDTH * scanLinesPerRow];
 
         // Populate the character
-        for (int i = 0; i < (CHAR_WIDTH * Math.min(CHAR_HEIGHT, scanLinesPerRow)); i++) {
+        arraycopy(charRom, romOffset, glyph, 0, CHAR_WIDTH * Math.min(CHAR_HEIGHT, scanLinesPerRow));
-            glyph[i] = charRom[romOffset + i];
-        }
 
         // Overlay the cursor
         if (!hideCursor && crtc.isCursorEnabled() && crtc.getCursorPosition() == address) {

src/main/java/com/loomcom/symon/util/FifoRingBuffer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -38,7 +38,7 @@ public class FifoRingBuffer<E> implements Iterable<E> {
     private int maxLength;
 
     public FifoRingBuffer(int maxLength) {
-        this.fifoBuffer = new LinkedList<E>();
+        this.fifoBuffer = new LinkedList<>();
         this.maxLength = maxLength;
     }
 

src/main/java/com/loomcom/symon/util/Utils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008-2013 Seth J. Morabito <sethm@loomcom.com>
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining
  * a copy of this software and associated documentation files (the
@@ -24,24 +24,9 @@
 package com.loomcom.symon.util;
 
 /**
- * Hex String Utilities.
+ * Various Utilities
- *
- * <p/>
- *
- * But why? Java, after all, has a number of ways to convert an integer into a hex string,
- * so it may look absurd to go to the trouble of writing yet another conversion! The answer is
- * performance.
- *
- * <p/>
- *
- * The most convenient way to get a formatted hex value from an integer is with the <code>String.format</code>
- * method, but this turns out to be extremely inefficient. Formatting a million integers
- * with <code>String.format</code> takes something like 1600ms. Formatting the same number of integers
- * with <code>HexUtil</code> takes only 160ms. This is on par with <code>Integer.toHexString</code>,
- * but also gives the desired padding.
- *
  */
-public class HexUtil {
+public class Utils {
 
     static final String NON_PRINTABLE = ".";
 
@@ -93,6 +78,7 @@ public class HexUtil {
 
     /**
      * Very fast 8-bit int to ASCII conversion.
+     *
      * @param val The value of an ASCII character.
      * @return A string representing the ASCII character.
      */
@@ -121,9 +107,13 @@ public class HexUtil {
      * @return Four digit, zero padded hexadecimal string.
      */
     public static String wordToHex(int val) {
-        StringBuilder sb = new StringBuilder(4);
+        return HEX_CONSTANTS[(val >> 8) & 0xff] + HEX_CONSTANTS[val & 0xff];
-        sb.append(HEX_CONSTANTS[(val >> 8) & 0xff]);
+    }
-        sb.append(HEX_CONSTANTS[val & 0xff]);
+
-        return sb.toString();
+    /**
+     * Given two bytes, return an address.
+     */
+    public static int address(int lowByte, int hiByte) {
+        return ((hiByte << 8) | lowByte) & 0xffff;
     }
 }

src/test/java/com/loomcom/symon/CpuImpliedModeTest.java

@@ -117,9 +117,22 @@ public class CpuImpliedModeTest {
     }
 
     @Test
-    public void test_BRK_HonorsIrqDisableFlag() throws MemoryAccessException {
+    public void test_BRK_IgnoresIrqDisableFlag() throws MemoryAccessException {
         cpu.setIrqDisableFlag();
 
+        cpu.setCarryFlag();
+        cpu.setOverflowFlag();
+        assertEquals(0x20 | Cpu.P_CARRY | Cpu.P_OVERFLOW | Cpu.P_IRQ_DISABLE,
+                     cpu.getProcessorStatus());
+        assertEquals(0x00, cpu.stackPeek());
+        assertFalse(cpu.getBreakFlag());
+        assertEquals(0x0200, cpu.getProgramCounter());
+        assertEquals(0xff, cpu.getStackPointer());
+        
+        // Set the IRQ vector
+        bus.write(0xffff, 0x12);
+        bus.write(0xfffe, 0x34);
+
         bus.loadProgram(0xea,
                         0xea,
                         0xea,
@@ -131,23 +144,26 @@ public class CpuImpliedModeTest {
 
         assertEquals(0x203, cpu.getProgramCounter());
 
-        // Triggers the BRK, which should do nothing because
+        // Triggers the BRK
-        // of the Interrupt Disable flag
         cpu.step();
 
-        // Reset to original contents of PC
-        assertEquals(0x0204, cpu.getProgramCounter());
-        // Empty stack
-        assertEquals(0xff, cpu.getStackPointer());
 
-        cpu.step(2); // Two more NOPs
+        // Was at PC = 0x204.  PC+1 should now be on the stack
+        assertEquals(0x02, bus.read(0x1ff)); // PC high byte
+        assertEquals(0x05, bus.read(0x1fe)); // PC low byte
+        assertEquals(0x20 | Cpu.P_CARRY | Cpu.P_OVERFLOW | Cpu.P_BREAK | Cpu.P_IRQ_DISABLE,
+                     bus.read(0x1fd));       // Processor Status, with B set
 
-        // Reset to original contents of PC
+        // Interrupt vector held 0x1234, so we should be there.
-        assertEquals(0x0206, cpu.getProgramCounter());
+        assertEquals(0x1234, cpu.getProgramCounter());
-        // Empty stack
+        assertEquals(0xfc, cpu.getStackPointer());
-        assertEquals(0xff, cpu.getStackPointer());
+
+        // B and I flags should have been set on P
+        assertEquals(0x20 | Cpu.P_CARRY | Cpu.P_OVERFLOW | Cpu.P_BREAK | Cpu.P_IRQ_DISABLE,
+                     cpu.getProcessorStatus());
     }
 
+
     /* CLC - Clear Carry Flag - $18 */
     @Test
     public void test_CLC() throws MemoryAccessException {

src/test/java/com/loomcom/symon/CpuIndirectIndexedModeTest.java

@@ -25,18 +25,10 @@ public class CpuIndirectIndexedModeTest {
         bus.write(0xfffd, (Bus.DEFAULT_LOAD_ADDRESS & 0xff00) >>> 8);
 
         cpu.reset();
-        // Assert initial state
-        assertEquals(0, cpu.getAccumulator());
-        assertEquals(0, cpu.getXRegister());
-        assertEquals(0, cpu.getYRegister());
-        assertEquals(0x200, cpu.getProgramCounter());
-        assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
     }
 
     @Test
     public void test_LDA() throws Exception {
-        assertEquals(cpu.toString(), 0x00, cpu.getAccumulator());
         bus.write(0x0014, 0x00);
         bus.write(0x0015, 0xd8);
         bus.write(0xd828, 0x03);

src/test/java/com/loomcom/symon/CpuIndirectModeTest.java

@@ -3,15 +3,19 @@ package com.loomcom.symon;
 import com.loomcom.symon.devices.Memory;
 import com.loomcom.symon.exceptions.MemoryAccessException;
 
-import junit.framework.TestCase;
+import org.junit.Before;
+import org.junit.Test;
 
-public class CpuIndirectModeTest extends TestCase {
+import static org.junit.Assert.assertEquals;
+
+public class CpuIndirectModeTest {
 
     protected Cpu    cpu;
     protected Bus    bus;
     protected Memory mem;
 
-    protected void setUp() throws Exception {
+    @Before
+    public void setUp() throws Exception {
         this.cpu = new Cpu();
         this.bus = new Bus(0x0000, 0xffff);
         this.mem = new Memory(0x0000, 0xffff);
@@ -41,6 +45,7 @@ public class CpuIndirectModeTest extends TestCase {
 
     /* JMP - Jump - $6c */
 
+    @Test
     public void test_JMP_notOnPageBoundary() throws MemoryAccessException {
         bus.write(0x3400, 0x00);
         bus.write(0x3401, 0x54);
@@ -51,6 +56,7 @@ public class CpuIndirectModeTest extends TestCase {
         assertEquals(0x20, cpu.getProcessorStatus());
     }
 
+    @Test
     public void test_JMP_with_ROR_Bug() throws MemoryAccessException {
         cpu.setBehavior(Cpu.CpuBehavior.NMOS_WITH_ROR_BUG);
         bus.write(0x3400, 0x22);
@@ -63,8 +69,9 @@ public class CpuIndirectModeTest extends TestCase {
         assertEquals(0x20, cpu.getProcessorStatus());
     }
 
+    @Test
     public void test_JMP_withIndirectBug() throws MemoryAccessException {
-        cpu.setBehavior(Cpu.CpuBehavior.NMOS_WITH_INDIRECT_JMP_BUG);
+        cpu.setBehavior(Cpu.CpuBehavior.NMOS_6502);
         bus.write(0x3400, 0x22);
         bus.write(0x34ff, 0x00);
         bus.write(0x3500, 0x54);
@@ -75,8 +82,9 @@ public class CpuIndirectModeTest extends TestCase {
         assertEquals(0x20, cpu.getProcessorStatus());
     }
 
+    @Test
     public void test_JMP_withOutIndirectBug() throws MemoryAccessException {
-        cpu.setBehavior(Cpu.CpuBehavior.NMOS_WITHOUT_INDIRECT_JMP_BUG);
+        cpu.setBehavior(Cpu.CpuBehavior.CMOS_6502);
         bus.write(0x3400, 0x22);
         bus.write(0x34ff, 0x00);
         bus.write(0x3500, 0x54);
@@ -87,8 +95,9 @@ public class CpuIndirectModeTest extends TestCase {
         assertEquals(0x20, cpu.getProcessorStatus());
     }
 
+    @Test
     public void test_JMP_cmos() throws MemoryAccessException {
-        cpu.setBehavior(Cpu.CpuBehavior.CMOS);
+        cpu.setBehavior(Cpu.CpuBehavior.CMOS_6502);
         bus.write(0x3400, 0x22);
         bus.write(0x34ff, 0x00);
         bus.write(0x3500, 0x54);

src/test/java/com/loomcom/symon/CpuIndirectXModeTest.java

@@ -3,14 +3,21 @@ package com.loomcom.symon;
 import com.loomcom.symon.devices.Memory;
 import com.loomcom.symon.exceptions.MemoryAccessException;
 import junit.framework.TestCase;
+import org.junit.Before;
+import org.junit.Test;
 
-public class CpuIndirectXModeTest extends TestCase {
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class CpuIndirectXModeTest {
 
     protected Cpu    cpu;
     protected Bus    bus;
     protected Memory mem;
 
-    protected void setUp() throws Exception {
+    @Before
+    public void setUp() throws Exception {
         this.cpu = new Cpu();
         this.bus = new Bus(0x0000, 0xffff);
         this.mem = new Memory(0x0000, 0xffff);
@@ -47,7 +54,7 @@ public class CpuIndirectXModeTest extends TestCase {
     */
 
     /* ORA - Logical Inclusive OR - $1d */
-
+    @Test
     public void test_ORA() throws MemoryAccessException {
         // Set some initial values in memory
         bus.write(0x2c30, 0x00);
@@ -93,7 +100,7 @@ public class CpuIndirectXModeTest extends TestCase {
     }
 
     /* AND - Logical AND - $3d */
-
+    @Test
     public void test_AND() throws MemoryAccessException {
         bus.write(0x1a30, 0x00);
         bus.write(0x1a31, 0x11);
@@ -153,7 +160,7 @@ public class CpuIndirectXModeTest extends TestCase {
     }
 
     /* EOR - Exclusive OR - $5d */
-
+    @Test
     public void test_EOR() throws MemoryAccessException {
         bus.write(0xab40, 0x00);
         bus.write(0xab41, 0xff);
@@ -189,7 +196,7 @@ public class CpuIndirectXModeTest extends TestCase {
     }
 
     /* ADC - Add with Carry - $7d */
-
+    @Test
     public void test_ADC() throws MemoryAccessException {
         bus.write(0xab40, 0x01);
         bus.write(0xab41, 0xff);
@@ -290,6 +297,7 @@ public class CpuIndirectXModeTest extends TestCase {
         assertTrue(cpu.getCarryFlag());
     }
 
+    @Test
     public void test_ADC_IncludesCarry() throws MemoryAccessException {
         bus.write(0xab40, 0x01);
 
@@ -307,6 +315,7 @@ public class CpuIndirectXModeTest extends TestCase {
         assertFalse(cpu.getCarryFlag());
     }
 
+    @Test
     public void test_ADC_DecimalMode() throws MemoryAccessException {
         bus.write(0xab40, 0x01);
         bus.write(0xab41, 0x99);
@@ -404,7 +413,7 @@ public class CpuIndirectXModeTest extends TestCase {
     }
 
     /* STA - Store Accumulator - $9d */
-
+    @Test
     public void test_STA() throws MemoryAccessException {
         cpu.setXRegister(0x30);
 
@@ -438,7 +447,7 @@ public class CpuIndirectXModeTest extends TestCase {
     }
 
     /* LDA - Load Accumulator - $bd */
-
+    @Test
     public void test_LDA() throws MemoryAccessException {
         bus.write(0xab42, 0x00);
         bus.write(0xab43, 0x0f);
@@ -467,7 +476,7 @@ public class CpuIndirectXModeTest extends TestCase {
     }
 
     /* CMP - Compare Accumulator - $dd */
-
+    @Test
     public void test_CMP() throws MemoryAccessException {
         bus.write(0xab40, 0x00);
         bus.write(0xab41, 0x80);
@@ -498,7 +507,7 @@ public class CpuIndirectXModeTest extends TestCase {
     }
 
     /* SBC - Subtract with Carry - $fd */
-
+    @Test
     public void test_SBC() throws MemoryAccessException {
         bus.write(0xab40, 0x01);
 
@@ -557,6 +566,7 @@ public class CpuIndirectXModeTest extends TestCase {
         assertTrue(cpu.getCarryFlag());
     }
 
+    @Test
     public void test_SBC_IncludesNotOfCarry() throws MemoryAccessException {
         bus.write(0xab40, 0x01);
 
@@ -602,6 +612,7 @@ public class CpuIndirectXModeTest extends TestCase {
 
     }
 
+    @Test
     public void test_SBC_DecimalMode() throws MemoryAccessException {
         bus.write(0xab40, 0x01);
         bus.write(0xab50, 0x11);

src/test/java/com/loomcom/symon/CpuTest.java

@@ -1,5 +1,6 @@
 package com.loomcom.symon;
 
+import com.loomcom.symon.util.Utils;
 import junit.framework.*;
 
 import com.loomcom.symon.devices.*;
@@ -240,6 +241,7 @@ public class CpuTest extends TestCase {
 
     public void testSetProcessorStatus() {
         // Default
+
         assertFalse(cpu.getZeroFlag());
         assertFalse(cpu.getZeroFlag());
         assertFalse(cpu.getIrqDisableFlag());
@@ -383,6 +385,41 @@ public class CpuTest extends TestCase {
         assertFalse(cpu.getCpuState().irqAsserted);
     }
 
+    public void testIrqDoesNotSetBRK() throws Exception {
+        // Ensure the IRQ disable flag is cleared
+        cpu.clearIrqDisableFlag();
+
+        // Set the IRQ vector
+        bus.write(0xffff, 0x12);
+        bus.write(0xfffe, 0x34);
+
+        // Create an IRQ handler at 0x1234
+        cpu.setProgramCounter(0x1234);
+        bus.loadProgram(0xa9, 0x33,  // LDA #$33
+                        0x69, 0x01); // ADC #$01
+
+        cpu.setProgramCounter(0x0200);
+        // Create a little program at 0x0200
+        bus.loadProgram(0x18,        // CLC
+                        0xa9, 0x01,  // LDA #$00
+                        0x69, 0x01); // ADC #$01
+
+        cpu.step();
+        assertEquals(0x0201, cpu.getProgramCounter()); // First instruction executed.
+        assertEquals(0x00, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x0203, cpu.getProgramCounter());
+        assertEquals(0x01, cpu.getAccumulator());
+
+        cpu.assertIrq();
+
+        cpu.step();
+        assertTrue(cpu.getIrqDisableFlag()); // Should have been set by the IRQ
+        assertFalse(cpu.getBreakFlag());
+
+    }
+
     public void testIrqHonorsIrqDisabledFlag() throws Exception {
         // Ensure the IRQ disable flag is set
         cpu.setIrqDisableFlag();
@@ -497,6 +534,37 @@ public class CpuTest extends TestCase {
         assertFalse(cpu.getCpuState().nmiAsserted);
     }
 
+    public void testNmiDoesNotSetBRK() throws Exception {
+        // Set the NMI vector to 0x1000
+        bus.write(0xfffb, 0x10);
+        bus.write(0xfffa, 0x00);
+
+        // Create an NMI handler at 0x1000
+        cpu.setProgramCounter(0x1000);
+        bus.loadProgram(0xa9, 0x33,  // LDA #$33
+                        0x69, 0x01); // ADC #$01
+
+        // Create a little program at 0x0200
+        cpu.setProgramCounter(0x0200);
+        bus.loadProgram(0x18,        // CLC
+                        0xa9, 0x01,  // LDA #$00
+                        0x69, 0x01); // ADC #$01
+
+        cpu.step();
+        assertEquals(0x0201, cpu.getProgramCounter()); // First instruction executed.
+        assertEquals(0x00, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x0203, cpu.getProgramCounter());
+        assertEquals(0x01, cpu.getAccumulator());
+
+        cpu.assertNmi();
+
+        cpu.step();
+        assertFalse(cpu.getBreakFlag());
+
+}
+
     public void testNmiIgnoresIrqDisableFlag() throws Exception {
         // Set the IRQ disable flag, which should be ignored by the NMI
         cpu.setIrqDisableFlag();
@@ -537,11 +605,11 @@ public class CpuTest extends TestCase {
 
 
     public void testAddress() {
-        assertEquals(0xf1ea, cpu.address(0xea, 0xf1));
+        assertEquals(0xf1ea, Utils.address(0xea, 0xf1));
-        assertEquals(0x00ea, cpu.address(0xea, 0x00));
+        assertEquals(0x00ea, Utils.address(0xea, 0x00));
-        assertEquals(0xf100, cpu.address(0x00, 0xf1));
+        assertEquals(0xf100, Utils.address(0x00, 0xf1));
-        assertEquals(0x1234, cpu.address(0x34, 0x12));
+        assertEquals(0x1234, Utils.address(0x34, 0x12));
-        assertEquals(0xffff, cpu.address(0xff, 0xff));
+        assertEquals(0xffff, Utils.address(0xff, 0xff));
     }
 
     public void testZpxAddress() {

src/test/java/com/loomcom/symon/CpuZeroPageIndirectTest.java

@@ -0,0 +1,329 @@
+package com.loomcom.symon;
+
+import com.loomcom.symon.devices.Memory;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertFalse;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Test for Zero Page Indirect addressing mode, found on some instructions
+ * in the 65C02 and 65816
+ */
+public class CpuZeroPageIndirectTest {
+    protected Cpu    cpu;
+    protected Bus    bus;
+    protected Memory mem;
+
+    private void makeCmosCpu() throws Exception {
+        makeCpu(InstructionTable.CpuBehavior.CMOS_6502);
+    }
+
+    private void makeNmosCpu() throws Exception {
+        makeCpu(InstructionTable.CpuBehavior.NMOS_6502);
+    }
+
+    private void makeCpu(InstructionTable.CpuBehavior behavior) throws Exception {
+        this.cpu = new Cpu(behavior);
+        this.bus = new Bus(0x0000, 0xffff);
+        this.mem = new Memory(0x0000, 0xffff);
+        bus.addCpu(cpu);
+        bus.addDevice(mem);
+
+        // Load the reset vector.
+        bus.write(0xfffc, Bus.DEFAULT_LOAD_ADDRESS & 0x00ff);
+        bus.write(0xfffd, (Bus.DEFAULT_LOAD_ADDRESS & 0xff00) >>> 8);
+
+        cpu.reset();
+    }
+
+    @Test
+    public void test_ora() throws Exception {
+        makeCmosCpu();
+
+        // Set some initial values in zero page.
+        bus.write(0x30, 0x00);
+        bus.write(0x31, 0x10);
+
+        bus.write(0x40, 0x01);
+        bus.write(0x41, 0x10);
+
+        bus.write(0x50, 0x02);
+        bus.write(0x51, 0x10);
+
+        bus.write(0x60, 0x03);
+        bus.write(0x61, 0x10);
+
+        bus.write(0x1000, 0x11);
+        bus.write(0x1001, 0x22);
+        bus.write(0x1002, 0x44);
+        bus.write(0x1003, 0x88);
+
+        bus.loadProgram(0x12, 0x30,  // ORA ($30)
+                        0x12, 0x40,  // ORA ($40)
+                        0x12, 0x50,  // ORA ($50)
+                        0x12, 0x60); // ORA ($60)
+
+
+        assertEquals(0x00, cpu.getAccumulator());
+
+        // 0x00 | 0x11 = 0x11
+        cpu.step();
+        assertEquals(0x11, cpu.getAccumulator());
+        assertFalse(cpu.getZeroFlag());
+        assertFalse(cpu.getNegativeFlag());
+
+        // 0x11 | 0x22 = 0x33
+        cpu.step();
+        assertEquals(0x33, cpu.getAccumulator());
+        assertFalse(cpu.getZeroFlag());
+        assertFalse(cpu.getNegativeFlag());
+
+        // 0x33 | 0x44 = 0x77
+        cpu.step();
+        assertEquals(0x77, cpu.getAccumulator());
+        assertFalse(cpu.getZeroFlag());
+        assertFalse(cpu.getNegativeFlag());
+
+        // 0x77 | 0x88 = 0xff
+        cpu.step();
+        assertEquals(0xff, cpu.getAccumulator());
+        assertFalse(cpu.getZeroFlag());
+        assertTrue(cpu.getNegativeFlag());
+    }
+
+    @Test
+    public void test_ora_requiresCmosCpu() throws Exception {
+        makeNmosCpu();
+
+        // Set some initial values in zero page.
+        bus.write(0x30, 0x00);
+        bus.write(0x31, 0x10);
+
+        bus.write(0x40, 0x01);
+        bus.write(0x41, 0x10);
+
+        bus.write(0x50, 0x02);
+        bus.write(0x51, 0x10);
+
+        bus.write(0x60, 0x03);
+        bus.write(0x61, 0x10);
+
+        bus.write(0x1000, 0x11);
+        bus.write(0x1001, 0x22);
+        bus.write(0x1002, 0x44);
+        bus.write(0x1003, 0x88);
+
+        bus.loadProgram(0x12, 0x30,  // ORA ($30)
+                        0x12, 0x40,  // ORA ($40)
+                        0x12, 0x50,  // ORA ($50)
+                        0x12, 0x60); // ORA ($60)
+
+
+        assertEquals(0x00, cpu.getAccumulator());
+
+        boolean zState = cpu.getZeroFlag();
+        boolean nState = cpu.getNegativeFlag();
+
+        // 0x00 | 0x11 = 0x11, but not implemented in NMOS cpu
+        cpu.step();
+        assertEquals(0x00, cpu.getAccumulator());
+        assertEquals(zState, cpu.getZeroFlag());         // unchanged
+        assertEquals(nState, cpu.getNegativeFlag());     // unchanged
+
+        // 0x11 | 0x22 = 0x33, but not implemented in NMOS cpu
+        cpu.step();
+        assertEquals(0x00, cpu.getAccumulator());
+        assertEquals(zState, cpu.getZeroFlag());         // unchanged
+        assertEquals(nState, cpu.getNegativeFlag());     // unchanged
+
+        // 0x33 | 0x44 = 0x77, but not implemented in NMOS cpu
+        cpu.step();
+        assertEquals(0x00, cpu.getAccumulator());
+        assertEquals(zState, cpu.getZeroFlag());         // unchanged
+        assertEquals(nState, cpu.getNegativeFlag());     // unchanged
+
+        // 0x77 | 0x88 = 0xff, but not implemented in NMOS cpu
+        cpu.step();
+        assertEquals(0x00, cpu.getAccumulator());
+        assertEquals(zState, cpu.getZeroFlag());         // unchanged
+        assertEquals(nState, cpu.getNegativeFlag());     // unchanged
+    }
+
+    @Test
+    public void test_and() throws Exception {
+        makeCmosCpu();
+
+        // Set some initial values in zero page.
+        bus.write(0x30, 0x00);
+        bus.write(0x31, 0x10);
+
+        bus.write(0x40, 0x01);
+        bus.write(0x41, 0x10);
+
+        bus.write(0x50, 0x02);
+        bus.write(0x51, 0x10);
+
+        bus.write(0x1000, 0x33);
+        bus.write(0x1001, 0x11);
+        bus.write(0x1002, 0x88);
+
+        bus.loadProgram(0x32, 0x30,  // AND ($30)
+                        0x32, 0x40,  // AND ($40)
+                        0x32, 0x50); // AND ($50)
+
+        cpu.setAccumulator(0xff);
+
+        // 0xFF & 0x33 == 0x33
+        cpu.step();
+        assertEquals(0x33, cpu.getAccumulator());
+        assertFalse(cpu.getZeroFlag());
+        assertFalse(cpu.getNegativeFlag());
+
+        // 0x33 & 0x11 == 0x11
+        cpu.step();
+        assertEquals(0x11, cpu.getAccumulator());
+        assertFalse(cpu.getZeroFlag());
+        assertFalse(cpu.getNegativeFlag());
+
+        // 0x11 & 0x80 == 0
+        cpu.step();
+        assertEquals(0, cpu.getAccumulator());
+        assertTrue(cpu.getZeroFlag());
+        assertFalse(cpu.getNegativeFlag());
+    }
+
+    @Test
+    public void test_and_requiresCmosCpu() throws Exception {
+        makeNmosCpu();
+
+        // Set some initial values in zero page.
+        bus.write(0x30, 0x00);
+        bus.write(0x31, 0x10);
+
+        bus.write(0x40, 0x01);
+        bus.write(0x41, 0x10);
+
+        bus.write(0x50, 0x02);
+        bus.write(0x51, 0x10);
+
+        bus.write(0x1000, 0x33);
+        bus.write(0x1001, 0x11);
+        bus.write(0x1002, 0x88);
+
+        bus.loadProgram(0x32, 0x30,  // AND ($30)
+                        0x32, 0x40,  // AND ($40)
+                        0x32, 0x50); // AND ($50)
+
+
+        cpu.setAccumulator(0xff);
+
+        boolean zState = cpu.getZeroFlag();
+        boolean nState = cpu.getNegativeFlag();
+
+        // 0xFF & 0x33 == 0x33, but not implemented in NMOS cpu
+        cpu.step();
+        assertEquals(0xff, cpu.getAccumulator());
+        assertEquals(zState, cpu.getZeroFlag());
+        assertEquals(nState, cpu.getNegativeFlag());
+
+        // 0x33 & 0x11 == 0x11, but not implemented in NMOS cpu
+        cpu.step();
+        assertEquals(0xff, cpu.getAccumulator());
+        assertEquals(zState, cpu.getZeroFlag());
+        assertEquals(nState, cpu.getNegativeFlag());
+
+        // 0x11 & 0x80 == 0, but not implemented in NMOS cpu
+        cpu.step();
+        assertEquals(0xff, cpu.getAccumulator());
+        assertEquals(zState, cpu.getZeroFlag());
+        assertEquals(nState, cpu.getNegativeFlag());
+    }
+
+    @Test
+    public void test_eor() throws Exception {
+        makeCmosCpu();
+
+        // Set some initial values in zero page.
+        bus.write(0x30, 0x00);
+        bus.write(0x31, 0x10);
+
+        bus.write(0x40, 0x01);
+        bus.write(0x41, 0x10);
+
+        bus.write(0x50, 0x02);
+        bus.write(0x51, 0x10);
+
+        bus.write(0x60, 0x03);
+        bus.write(0x61, 0x10);
+
+        bus.write(0x1000, 0x00);
+        bus.write(0x1001, 0xff);
+        bus.write(0x1002, 0x33);
+        bus.write(0x1003, 0x44);
+
+        bus.loadProgram(0x52, 0x30,  // AND ($30)
+                        0x52, 0x40,  // AND ($40)
+                        0x52, 0x50,  // EOR ($50)
+                        0x52, 0x60); // AND ($60)
+
+
+        cpu.setAccumulator(0x88);
+
+        cpu.step();
+        assertEquals(0x88, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x77, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x44, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x00, cpu.getAccumulator());
+    }
+
+    @Test
+    public void test_eor_requiresCmosCpu() throws Exception {
+        makeNmosCpu();
+
+        // Set some initial values in zero page.
+        bus.write(0x30, 0x00);
+        bus.write(0x31, 0x10);
+
+        bus.write(0x40, 0x01);
+        bus.write(0x41, 0x10);
+
+        bus.write(0x50, 0x02);
+        bus.write(0x51, 0x10);
+
+        bus.write(0x60, 0x03);
+        bus.write(0x61, 0x10);
+
+        bus.write(0x1000, 0x00);
+        bus.write(0x1001, 0xff);
+        bus.write(0x1002, 0x33);
+        bus.write(0x1003, 0x44);
+
+        bus.loadProgram(0x52, 0x30,  // AND ($30)
+                        0x52, 0x40,  // AND ($40)
+                        0x52, 0x50,  // EOR ($50)
+                        0x52, 0x60); // AND ($60)
+
+
+        cpu.setAccumulator(0x88);
+
+        cpu.step();
+        assertEquals(0x88, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x88, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x88, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x88, cpu.getAccumulator());
+    }
+}

src/test/java/com/loomcom/symon/CrtcTest.java

@@ -19,19 +19,17 @@ import static org.mockito.Mockito.*;
 public class CrtcTest {
 
     Crtc crtc;
+    Memory memory;
 
     @Mock
     DeviceChangeListener changeListener;
-    @Mock
-    Memory memory;
 
     @Before
     public void createDevices() throws Exception {
+        memory = new Memory(0, 0x7fff);
+
         crtc = new Crtc(0x9000, memory);
         crtc.registerListener(changeListener);
-
-        when(memory.startAddress()).thenReturn(0);
-        when(memory.endAddress()).thenReturn(0x7fff);
     }
 
     @Test
@@ -340,4 +338,58 @@ public class CrtcTest {
         crtc.write(1, 0x80); // Can't position cursor
     }
 
+    @Test
+    public void shouldSetRowColumnAddressing() throws Exception {
+        assertEquals(false, crtc.getRowColumnAddressing());
+        crtc.write(0, 8);        // Select mode control register
+        crtc.write(1, 0x04);
+        assertEquals(true, crtc.getRowColumnAddressing());
+    }
+
+    @Test
+    public void shouldSetDisplayEnableSkew() throws Exception {
+        assertEquals(false, crtc.getDisplayEnableSkew());
+        crtc.write(0, 8);        // Select mode control register
+        crtc.write(1, 0x10);
+        assertEquals(true, crtc.getDisplayEnableSkew());
+    }
+
+    @Test
+    public void shouldSetCursorSkew() throws Exception {
+        assertEquals(false, crtc.getCursorSkew());
+        crtc.write(0, 8);        // Select mode control register
+        crtc.write(1, 0x20);
+        assertEquals(true, crtc.getCursorSkew());
+    }
+
+    @Test
+    public void shouldDoStraightBinaryAddressing() throws Exception {
+        crtc.write(0, 8);
+        crtc.write(1, 0); // Select straight binary addressing
+
+        // Fill the memory with a repeating pattern
+        int videoMemoryBase = 0x7000;
+        int j = 0;
+
+        for (int i = 0; i < 2048; i++) {
+            memory.write(videoMemoryBase + i, j);
+            if (j == 255) {
+                j = 0;
+            } else {
+                j++;
+            }
+        }
+
+        // Now verify that straight-binary addressing of the CRTC works
+        j = 0;
+
+        for (int i = 0; i < 2048; i++) {
+            assertEquals(j, crtc.getCharAtAddress(videoMemoryBase + i));
+            if (j == 255) {
+                j = 0;
+            } else {
+                j++;
+            }
+        }
+    }
 }

src/test/java/com/loomcom/symon/HexUtilTest.java

@@ -1,42 +0,0 @@
-package com.loomcom.symon;
-
-import com.loomcom.symon.util.HexUtil;
-import junit.framework.TestCase;
-
-public class HexUtilTest extends TestCase {
-    public void testByteToHex() {
-        assertEquals("FE", HexUtil.byteToHex(0xfe));
-        assertEquals("00", HexUtil.byteToHex(0));
-        assertEquals("0A", HexUtil.byteToHex(10));
-    }
-
-    public void testByteToHexIgnoresSign() {
-        assertEquals("FF", HexUtil.byteToHex(-1));
-    }
-
-    public void testByteToHexMasksLowByte() {
-        assertEquals("FE", HexUtil.byteToHex(0xfffe));
-        assertEquals("00", HexUtil.byteToHex(0xff00));
-    }
-
-    public void testWordToHex() {
-        assertEquals("0000", HexUtil.wordToHex(0));
-        assertEquals("FFFF", HexUtil.wordToHex(65535));
-        assertEquals("FFFE", HexUtil.wordToHex(65534));
-    }
-
-    public void testWordToHexIgnoresSign() {
-        assertEquals("FFFF", HexUtil.wordToHex(-1));
-    }
-
-    public void testWordToHexMasksTwoLowBytes() {
-        assertEquals("FFFE", HexUtil.wordToHex(0xfffffe));
-        assertEquals("FF00", HexUtil.wordToHex(0xffff00));
-    }
-
-    public void testAllBytesAreCorrect() {
-        for (int i = 0; i <= 0xff; i++) {
-            assertEquals(String.format("%02X", i), HexUtil.byteToHex(i));
-        }
-    }
-}

src/test/java/com/loomcom/symon/UtilsTest.java

@@ -0,0 +1,42 @@
+package com.loomcom.symon;
+
+import com.loomcom.symon.util.Utils;
+import junit.framework.TestCase;
+
+public class UtilsTest extends TestCase {
+    public void testByteToHex() {
+        assertEquals("FE", Utils.byteToHex(0xfe));
+        assertEquals("00", Utils.byteToHex(0));
+        assertEquals("0A", Utils.byteToHex(10));
+    }
+
+    public void testByteToHexIgnoresSign() {
+        assertEquals("FF", Utils.byteToHex(-1));
+    }
+
+    public void testByteToHexMasksLowByte() {
+        assertEquals("FE", Utils.byteToHex(0xfffe));
+        assertEquals("00", Utils.byteToHex(0xff00));
+    }
+
+    public void testWordToHex() {
+        assertEquals("0000", Utils.wordToHex(0));
+        assertEquals("FFFF", Utils.wordToHex(65535));
+        assertEquals("FFFE", Utils.wordToHex(65534));
+    }
+
+    public void testWordToHexIgnoresSign() {
+        assertEquals("FFFF", Utils.wordToHex(-1));
+    }
+
+    public void testWordToHexMasksTwoLowBytes() {
+        assertEquals("FFFE", Utils.wordToHex(0xfffffe));
+        assertEquals("FF00", Utils.wordToHex(0xffff00));
+    }
+
+    public void testAllBytesAreCorrect() {
+        for (int i = 0; i <= 0xff; i++) {
+            assertEquals(String.format("%02X", i), Utils.byteToHex(i));
+        }
+    }
+}