Prepare release 1.4.0

This change introduces a new command line flag, '-b', that cause the
simulator to halt on the `BRK` instruction. By default, however, the
simulator will no longer halt on `BRK`.

As before, this behavior can be toggled in the preferences at run-time.

.gitignore

@@ -1,6 +1,8 @@
 *~
+*.jar
 *#
 target
 .DS_Store
 .idea
 symon.iml
+/dependency-reduced-pom.xml

README.md

@@ -1,9 +1,9 @@
 SYMON - A 6502 System Simulator
 ===============================
 
-**Version:** 1.3.1
+**Version:** 1.3.2
 
-**Last Updated:** 12 October, 2019
+**Last Updated:** 08 March, 2021
 
 See the file COPYING for license.
 
@@ -36,8 +36,8 @@ are always welcome.
 
 ## 3.0 Features
 
-Symon can simulate multiple 6502 based architectures. At present, three
+Symon can simulate multiple 6502 based architectures. At present, four
-machines are implemented: Symon (the default), MULTICOMP, and a "Simple"
+machines are implemented: Symon (the default), MULTICOMP, BenEater, and a "Simple"
 machine useful for debugging.
 
 ### 3.1 Memory Maps
@@ -64,19 +64,41 @@ memory.
 
   - `$0000`--`$FFFF`: 64KB RAM
 
+#### 3.1.4 BenEater Memory Map
+
+  - `$0000`--`$3FFF`: 16KB RAM
+  - `$5000`--`$5003`: MOS 6551 ACIA (Serial Console)
+  - `$6000`--`$600F`: 6522 VIA
+  - `$8000`--`$FFFF`: 16KB ROM
+
 ### 3.2 Serial Console and CPU Status
 
 ![Serial Console](https://github.com/sethm/symon/raw/master/screenshots/console.png)
 
 The main window of the simulator acts as the primary Input/Output
-system through a virtual serial terminal. The terminal is attached to
+system through a virtual serial terminal. It also provides CPU status.
-a simulated ACIA, including a programmable baud rate generator that
+Contents of the accumulator, index registers, processor status flags,
-tries to approximate the correct "feel" of the programmed baud rate.
+disassembly of the instruction register, and stack pointer are all displayed.
-(The sample Enhanced BASIC ROM image is programmed for 9600 baud)
 
-It also provides CPU status. Contents of the accumulator, index
+The terminal is attached to a simulated MOS 6551 ACIA. It behaves very much
-registers, processor status flags, disassembly of the instruction
+as described in the datasheet, with some exceptions:
-register, and stack pointer are all displayed.
+
+  - The simulated ACIA is permanently connected to the virtual terminal,
+    the Data Carrier Detect and Data Set Ready status bits always indicate
+    a connection is ready.
+  - The parity, stop-bits and bits-per-character settings are ignored. The
+    ACIA always sends and receives 8-bit characters, and parity errors
+    do not occur.
+  - The ACIA tries to honour the configured baud rate, but as a special case
+    the default "16x External Clock" rate is interpreted to mean "as fast as
+    possible" (The sample Enhanced BASIC ROM image is programmed for 9600 baud).
+  - The ACIA ignores the configured state of the Data Terminal Ready pin;
+    it is always ready to receive and transmit.
+
+For more information on the MOS 6551 ACIA and its programming model,
+see the official datasheet:
+
+  - [MOS 6551 ACIA](http://archive.6502.org/datasheets/mos_6551_acia.pdf)
 
 ![Font Selection](https://github.com/sethm/symon/raw/master/screenshots/font_selection.png)
 
@@ -198,12 +220,14 @@ interface.
 Two command line options may be passed to the JAR file on startup,
 to specify machine type and CPU type. The options are:
 
-  - `-cpu 6502`: Use the NMOS 6502 CPU type by default.
+  - `-c`,`-cpu 6502`: Use the NMOS 6502 CPU type by default.
-  - `-cpu 65c02`: Use the CMOS 65C02 CPU type by default.
+  - `-c`,`-cpu 65c02`: Use the CMOS 65C02 CPU type by default.
-  - `-machine symon`: Use the **Symon** machine type by default.
+  - `-c`,`-machine symon`: Use the **Symon** machine type by default.
-  - `-machine multicomp`: Use the **Multicomp** machine type by default.
+  - `-c`,`-machine multicomp`: Use the **Multicomp** machine type by default.
-  - `-machine simple`: Use the **Simple** machine type by default.
+  - `-m`,`-machine simple`: Use the **Simple** machine type by default.
-  - `-rom <file>`: Use the specified file as the ROM image.
+  - `-m`,`-machine beneater`: Use the **BenEater** machine type by default.
+  - `-r`,`-rom <file>`: Use the specified file as the ROM image.
+  - `-b`,`-brk`: Halt the simulator on a BRK instruction (default is to continue)
 
 ### 4.2 ROM images
 
@@ -212,10 +236,9 @@ properly. Without a ROM in memory, the simulator will not be able to
 reset, since the reset vector for the 6502 is located in the ROM
 address space.
 
-By default, any file named `rom.bin` that exists in the same directory
+ROM images can be loaded with the `-rom` argument when running
-where Symon is launched will be loaded as a ROM image. ROM images can
+Symon from the command line. ROM images can also be swapped out at
-also be swapped out at run-time with the "Load ROM Image..." in the
+run-time with the "Load ROM..." item in the File menu.
-File menu.
 
 The "samples" directory contains a ROM image for the Symon
 architecture named 'ehbasic.rom', containing Lee Davison's Enhanced
@@ -247,6 +270,16 @@ running.
 
 ## 5.0 Revision History
 
+  - **1.4.0:** 11 November 2023 - Adds a new machine, the Ben Eater
+    machine.  Correct handling of 6551 interrupts, and several 6551
+    bug fixes. Fixes power-on status of 6502 status register. Fixes a
+    bug with ASCII backspace character not moving the cursor
+    backwards. Finally, "halt on BRK" is no longer enabled by default,
+    but can be set at runtime or by a command line flag. Thank you to
+    Tim Allen and Chelsea Wilkinson for contributions!
+
+  - **1.3.2:** 8 March 2022 - Minor bug fixes.
+
   - **1.3.1:** 12 October, 2019 - Add support for new command line
     option `-cpu <type>` to specify one of `6502` or `65c02` on startup,
     and new option `-rom <file>` to specify a ROM file to load.
@@ -347,6 +380,8 @@ running.
 **Copyright (c) 2014 Seth J. Morabito &lt;web@loomcom.com&gt;**
 
 Portions Copyright (c) 2014 Maik Merten &lt;maikmerten@googlemail.com&gt;
+Portions Copyright (c) 2022 Tim Allen &lt;thristian@gmail.com&gt;
+Portions Copyright (c) 2023 Chelsea Wilkinson &lt;mail@chelseawilkinson.me&gt;
 
 Additional components used in this project are copyright their respective owners.
 
@@ -356,7 +391,7 @@ Additional components used in this project are copyright their respective owners
 
 This project would not have been possible without the following resources:
 
-  - [Andrew Jacobs' 6502 Pages](http://www.obelisk.demon.co.uk/6502/), for
+  - [Andrew Jacobs' 6502 Pages](http://obelisk.me.uk/6502/), for
     wonderfully detailed information about the 6502
 
   - [Neil Parker's "The 6502/65C02/65C816 Instruction Set Decoded"](http://www.llx.com/~nparker/a2/opcodes.html),

pom.xml

@@ -4,7 +4,7 @@
     <groupId>com.loomcom.symon</groupId>
     <artifactId>symon</artifactId>
     <packaging>jar</packaging>
-    <version>1.3.1</version>
+    <version>1.4.0</version>
     <name>symon</name>
     <url>http://www.loomcom.com/symon</url>
     <properties>
@@ -19,24 +19,24 @@
         <dependency>
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-classic</artifactId>
-            <version>1.2.3</version>
+            <version>1.4.5</version>
         </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
-            <version>4.12</version>
+            <version>4.13.2</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>org.mockito</groupId>
-            <artifactId>mockito-all</artifactId>
+            <artifactId>mockito-core</artifactId>
-            <version>1.10.19</version>
+            <version>4.8.0</version>
             <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>commons-cli</groupId>
             <artifactId>commons-cli</artifactId>
-            <version>1.4</version>
+            <version>1.5.0</version>
         </dependency>
     </dependencies>
 
@@ -44,24 +44,31 @@
         <plugins>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-assembly-plugin</artifactId>
+                <artifactId>maven-shade-plugin</artifactId>
-                <version>2.6</version>
+                <version>3.2.0</version>
                 <configuration>
-                    <descriptorRefs>
+                    <transformers>
-                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                        <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
-                    </descriptorRefs>
-                    <appendAssemblyId>false</appendAssemblyId>
-                    <archive>
-                        <manifest>
                             <mainClass>com.loomcom.symon.Main</mainClass>
-                        </manifest>
+                        </transformer>
-                    </archive>
+                    </transformers>
+                    <filters>
+                        <filter>
+                            <artifact>*:*</artifact>
+                            <excludes>
+                                <exclude>META-INF/*.SF</exclude>
+                                <exclude>META-INF/*.DSA</exclude>
+                                <exclude>META-INF/*.RSA</exclude>
+                            </excludes>
+                        </filter>
+                    </filters>
                 </configuration>
                 <executions>
                     <execution>
+                        <id>make-assembly</id>
                         <phase>package</phase>
                         <goals>
-                            <goal>single</goal>
+                            <goal>shade</goal>
                         </goals>
                     </execution>
                 </executions>
@@ -72,8 +79,8 @@
                 <version>3.7.0</version>
                 <configuration>
                     <compilerArgument>-Xlint:unchecked</compilerArgument>
-                    <source>1.7</source>
+                    <source>11</source>
-                    <target>1.7</target>
+                    <target>11</target>
                 </configuration>
             </plugin>
 
@@ -81,7 +88,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-jar-plugin</artifactId>
-                <version>2.6</version>
+                <version>3.2.0</version>
                 <configuration>
                     <archive>
                         <manifest>

samples/README

@@ -11,7 +11,6 @@ Sample Programs
   When loaded at address $0300, this program will echo back to the console
   anything typed.
 
-
 Both hello.prg and echo_poll.prg were assembled with the Ophis assembler:
 
    https://hkn.eecs.berkeley.edu/~mcmartin/ophis/
@@ -19,23 +18,25 @@ Both hello.prg and echo_poll.prg were assembled with the Ophis assembler:
 3. echo_irq.rom
 
   This is another echo program, and behaves identically to echo_poll.prg,
-  except it is interrupt-driven.
+  except it is interrupt-driven. This ROM can be loaded either through the
+  "File->Load ROM..." menu in Symon, or by specifying the path to
+  "echo_irq.rom" with the "-jar" command line option when running Symon,
+  for example: `java -jar symon-1.3.2.jar -rom samples/echo_irq.rom`
 
 4. ehbasic.rom
 
    This is Lee Davison's Enhanced 6502 BASIC.
 
-   To use this ROM image, just copy the file 'ehbasic.rom' into the directory
+   The EhBASIC ROM can be loaded either through the "File -> Load ROM..."
-   where you run Symon. Rename the file to 'rom.bin'.  When you start Symon,
+   menu in Symon, or by specifying the path to "ehbasic.rom" with
-   the ROM file will be automatically loaded at address $d000.
+   the "-jar" command line option when running Symon, for example:
+   `java -jar symon-1.3.2.jar -rom samples/ehbasic.rom`
 
    Click the "Run" button and EhBASIC should automatically start running.
 
    Type 'C' to do a cold start.
 
-   Then, type $C000 when prompted for the memory size.
+   Then, type '49152' (without the quotes) when prompted for the memory size.
-
-   NOTE: EhBASIC only wants upper-case input. This confused me at first!
 
    More information can be found in the 'ehbasic' directory, and by visiting
    the EhBASIC web page:

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

@@ -15,7 +15,7 @@
  * 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
+ * NON-INFRINGEMENT. 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.
@@ -32,7 +32,7 @@ import org.slf4j.LoggerFactory;
 /**
  * This class provides a simulation of the MOS 6502 CPU's state machine.
  * A simple interface allows this 6502 to read and write to a simulated bus,
- * and exposes some of the internal state for inspection and debugging.
+ * and exposes some internal state for inspection and debugging.
  */
 public class Cpu implements InstructionTable {
 
@@ -126,7 +126,7 @@ public class Cpu implements InstructionTable {
         // Clear status register bits.
         state.carryFlag = false;
         state.zeroFlag = false;
-        state.irqDisableFlag = false;
+        state.irqDisableFlag = true;
         state.decimalModeFlag = false;
         state.breakFlag = false;
         state.overflowFlag = false;
@@ -283,7 +283,7 @@ public class Cpu implements InstructionTable {
         // Execute
         switch (state.ir) {
 
-            /** Single Byte Instructions; Implied and Relative **/
+            // Single Byte Instructions; Implied and Relative
             case 0x00: // BRK - Force Interrupt - Implied
                 handleBrk(state.pc + 1);
                 break;
@@ -457,7 +457,7 @@ public class Cpu implements InstructionTable {
                 setArithmeticFlags(state.x);
                 break;
 
-            /** JMP *****************************************************************/
+            // JMP
             case 0x4c: // JMP - Absolute
                 state.pc = Utils.address(state.args[0], state.args[1]);
                 break;
@@ -495,7 +495,7 @@ public class Cpu implements InstructionTable {
                 state.pc = Utils.address(bus.read(lo, true), bus.read(hi, true));
                 break;
 
-            /** ORA - Logical Inclusive Or ******************************************/
+            // ORA - Logical Inclusive Or
             case 0x09: // #Immediate
                 state.a |= state.args[0];
                 setArithmeticFlags(state.a);
@@ -517,7 +517,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** ASL - Arithmetic Shift Left *****************************************/
+            // ASL - Arithmetic Shift Left
             case 0x0a: // Accumulator
                 state.a = asl(state.a);
                 setArithmeticFlags(state.a);
@@ -532,7 +532,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** BIT - Bit Test ******************************************************/
+            // BIT - Bit Test
             case 0x89: // 65C02 #Immediate
                 setZeroFlag((state.a & state.args[0]) == 0);
                 break;
@@ -551,7 +551,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** AND - Logical AND ***************************************************/
+            // AND - Logical AND
             case 0x29: // #Immediate
                 state.a &= state.args[0];
                 setArithmeticFlags(state.a);
@@ -573,7 +573,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** ROL - Rotate Left ***************************************************/
+            // ROL - Rotate Left
             case 0x2a: // Accumulator
                 state.a = rol(state.a);
                 setArithmeticFlags(state.a);
@@ -588,7 +588,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** EOR - Exclusive OR **************************************************/
+            // EOR - Exclusive OR
             case 0x49: // #Immediate
                 state.a ^= state.args[0];
                 setArithmeticFlags(state.a);
@@ -610,7 +610,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** LSR - Logical Shift Right *******************************************/
+            // LSR - Logical Shift Right
             case 0x4a: // Accumulator
                 state.a = lsr(state.a);
                 setArithmeticFlags(state.a);
@@ -625,7 +625,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** ADC - Add with Carry ************************************************/
+            // ADC - Add with Carry
             case 0x69: // #Immediate
                 if (state.decimalModeFlag) {
                     state.a = adcDecimal(state.a, state.args[0]);
@@ -653,7 +653,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** ROR - Rotate Right **************************************************/
+            // ROR - Rotate Right
             case 0x6a: // Accumulator
                 state.a = ror(state.a);
                 setArithmeticFlags(state.a);
@@ -668,7 +668,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** STA - Store Accumulator *********************************************/
+            // STA - Store Accumulator
             case 0x92: // 65C02 STA (ZP)
                 if (behavior == CpuBehavior.NMOS_6502 ||
                     behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
@@ -685,7 +685,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** STY - Store Y Register **********************************************/
+            // STY - Store Y Register
             case 0x84: // Zero Page
             case 0x8c: // Absolute
             case 0x94: // Zero Page,X
@@ -693,14 +693,14 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** STX - Store X Register **********************************************/
+            // STX - Store X Register
             case 0x86: // Zero Page
             case 0x8e: // Absolute
             case 0x96: // Zero Page,Y
                 bus.write(effectiveAddress, state.x);
                 break;
 
-            /** STZ - 65C02 Store Zero ****************************************************/
+            // STZ - 65C02 Store Zero
             case 0x64: // Zero Page
             case 0x74: // Zero Page,X
             case 0x9c: // Absolute
@@ -712,7 +712,7 @@ public class Cpu implements InstructionTable {
                 bus.write(effectiveAddress, 0);
                 break;
 
-            /** LDY - Load Y Register ***********************************************/
+            // LDY - Load Y Register
             case 0xa0: // #Immediate
                 state.y = state.args[0];
                 setArithmeticFlags(state.y);
@@ -726,7 +726,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** LDX - Load X Register ***********************************************/
+            // LDX - Load X Register
             case 0xa2: // #Immediate
                 state.x = state.args[0];
                 setArithmeticFlags(state.x);
@@ -740,7 +740,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** LDA - Load Accumulator **********************************************/
+            // LDA - Load Accumulator
             case 0xa9: // #Immediate
                 state.a = state.args[0];
                 setArithmeticFlags(state.a);
@@ -762,7 +762,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** CPY - Compare Y Register ********************************************/
+            // CPY - Compare Y Register
             case 0xc0: // #Immediate
                 cmp(state.y, state.args[0]);
                 break;
@@ -772,7 +772,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** CMP - Compare Accumulator *******************************************/
+            // CMP - Compare Accumulator
             case 0xc9: // #Immediate
                 cmp(state.a, state.args[0]);
                 break;
@@ -792,7 +792,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** DEC - Decrement Memory **********************************************/
+            // DEC - Decrement Memory
             case 0x3a: // 65C02 Immediate
                 if (behavior == CpuBehavior.NMOS_6502 ||
                     behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
@@ -811,7 +811,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** CPX - Compare X Register ********************************************/
+            // CPX - Compare X Register
             case 0xe0: // #Immediate
                 cmp(state.x, state.args[0]);
                 break;
@@ -821,7 +821,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** SBC - Subtract with Carry (Borrow) **********************************/
+            // SBC - Subtract with Carry (Borrow)
             case 0xe9: // #Immediate
                 if (state.decimalModeFlag) {
                     state.a = sbcDecimal(state.a, state.args[0]);
@@ -849,7 +849,7 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** INC - Increment Memory **********************************************/
+            // INC - Increment Memory
             case 0x1a: // 65C02 Increment Immediate
                 if (behavior == CpuBehavior.NMOS_6502 ||
                     behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
@@ -868,14 +868,14 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** 65C02 RMB - Reset Memory Bit **************************************/
+            // 65C02 RMB - Reset Memory Bit
             case 0x07: // 65C02 RMB0 - Zero Page
                 if (behavior == CpuBehavior.NMOS_6502 ||
                     behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true) & 0xff;
-                tmp &= ~(1 << 0);
+                tmp &= ~1;
                 bus.write(effectiveAddress, tmp);
                 break;
             case 0x17: // 65C02 RMB1 - Zero Page
@@ -943,14 +943,14 @@ public class Cpu implements InstructionTable {
                 break;
 
 
-            /** 65C02 SMB - Set Memory Bit **************************************/
+            // 65C02 SMB - Set Memory Bit
             case 0x87: // 65C02 SMB0 - Zero Page
                 if (behavior == CpuBehavior.NMOS_6502 ||
                     behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true) & 0xff;
-                tmp |= (1);
+                tmp |= 1;
                 bus.write(effectiveAddress, tmp);
                 break;
             case 0x97: // 65C02 SMB1 - Zero Page
@@ -1017,7 +1017,7 @@ public class Cpu implements InstructionTable {
                 bus.write(effectiveAddress, tmp);
                 break;
 
-            /** 65C02 TRB/TSB - Test and Reset Bit/Test and Set Bit ***************/
+            // 65C02 TRB/TSB - Test and Reset Bit/Test and Set Bit
             case 0x14: // 65C02 TRB - Test and Reset bit - Zero Page
             case 0x1c: // 65C02 TRB - Test and Reset bit - Absolute
                 if (behavior == CpuBehavior.NMOS_6502 ||
@@ -1026,8 +1026,9 @@ public class Cpu implements InstructionTable {
                 }
                 tmp = bus.read(effectiveAddress, true);
                 setZeroFlag((state.a & tmp) == 0);
-                tmp = (tmp &= ~(state.a)) & 0xff;
+                tmp &= ~(state.a);
-                bus.write(effectiveAddress,tmp);
+                tmp &= 0xff;
+                bus.write(effectiveAddress, tmp);
                 break;
 
             case 0x04: // 65C02 TSB - Test and Set bit - Zero Page
@@ -1038,18 +1039,19 @@ public class Cpu implements InstructionTable {
                 }
                 tmp = bus.read(effectiveAddress, true);
                 setZeroFlag((state.a & tmp) == 0);
-                tmp = (tmp |= (state.a)) & 0xff;
+                tmp |= state.a;
+                tmp = tmp & 0xff;
                 bus.write(effectiveAddress,tmp);
                 break;
 
-            /** 65C02 BBR - Branch if Bit Reset *************************************/
+            // 65C02 BBR - Branch if Bit Reset
             case 0x0f: // 65C02 BBR - Branch if bit 0 reset - Zero Page
                 if (behavior == CpuBehavior.NMOS_6502 ||
                     behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 0) == 0) {
+                if ((tmp & 1) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1060,7 +1062,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 1) == 0) {
+                if ((tmp & (1 << 1)) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1071,7 +1073,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 2) == 0) {
+                if ((tmp & (1 << 2)) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1082,7 +1084,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 3) == 0) {
+                if ((tmp & (1 << 3)) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1093,7 +1095,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 4) == 0) {
+                if ((tmp & (1 << 4)) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1105,7 +1107,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 5) == 0) {
+                if ((tmp & (1 << 5)) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1116,7 +1118,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 6) == 0) {
+                if ((tmp & (1 << 6)) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1127,20 +1129,20 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 7) == 0) {
+                if ((tmp & (1 << 7)) == 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
 
 
-            /** 65C02 BBS - Branch if Bit Set  ************************************/
+            // 65C02 BBS - Branch if Bit Set
             case 0x8f: // 65C02 BBS - Branch if bit 0 set - Zero Page
                 if (behavior == CpuBehavior.NMOS_6502 ||
                     behavior == CpuBehavior.NMOS_WITH_ROR_BUG) {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 0) > 0) {
+                if ((tmp & 1) != 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1151,7 +1153,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 1) > 0) {
+                if ((tmp & (1 << 1)) != 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1162,7 +1164,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 2) > 0) {
+                if ((tmp & (1 << 2)) > 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1173,7 +1175,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 3) > 0) {
+                if ((tmp & (1 << 3)) > 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1185,7 +1187,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 4) > 0) {
+                if ((tmp & (1 << 4)) > 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1197,7 +1199,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 5) > 0) {
+                if ((tmp & (1 << 5)) > 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1208,7 +1210,7 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 6) > 0) {
+                if ((tmp & (1 << 6)) > 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
@@ -1219,13 +1221,13 @@ public class Cpu implements InstructionTable {
                     break;
                 }
                 tmp = bus.read(effectiveAddress, true);
-                if ((tmp & 1 << 7) > 0) {
+                if ((tmp & (1 << 7)) > 0) {
                     state.pc = relAddress(state.args[1]);
                 }
                 break;
 
 
-            /** Unimplemented Instructions ****************************************/
+            // Unimplemented Instructions
             // TODO: Create a flag to enable highly-accurate emulation of unimplemented instructions.
             default:
                 setOpTrap();
@@ -1234,7 +1236,7 @@ public class Cpu implements InstructionTable {
 
         delayLoop(state.ir);
 
-        // Peek ahead to the next insturction and arguments
+        // Peek ahead to the next instruction and arguments
         peekAhead();
     }
 
@@ -1265,7 +1267,7 @@ public class Cpu implements InstructionTable {
     /**
      * Handle the common behavior of BRK, /IRQ, and /NMI
      *
-     * @throws MemoryAccessException
+     * @throws MemoryAccessException on memory access failure
      */
     private void handleInterrupt(int returnPc, int vectorLow, int vectorHigh, boolean isBreak) throws MemoryAccessException {
 
@@ -1674,7 +1676,7 @@ public class Cpu implements InstructionTable {
     public void setProgramCounter(int addr) {
         state.pc = addr;
 
-        // As a side-effect of setting the program counter,
+        // As a side effect of setting the program counter,
         // we want to peek ahead at the next state.
         try {
             peekAhead();
@@ -1971,7 +1973,7 @@ public class Cpu implements InstructionTable {
      */
     public String disassembleOpAtAddress(int address) throws MemoryAccessException {
         int opCode = bus.read(address, true);
-        int args[] = new int[2];
+        int[] args = new int[2];
         int size = Cpu.instructionSizes[opCode];
         for (int i = 1; i < size; i++) {
             int nextRead = (address + i) % bus.endAddress();

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

@@ -12,7 +12,7 @@ public class CpuState {
     public int a;
 
     /**
-     * X index regsiter
+     * X index register
      */
     public int x;
 
@@ -61,13 +61,12 @@ public class CpuState {
     public CpuState() {}
 
     /**
-     * Snapshot a copy of the 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)
-     * (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.
      */
+    @SuppressWarnings("CopyConstructorMissesField")
     public CpuState(CpuState s) {
         this.a = s.a;
         this.x = s.x;
@@ -83,6 +82,7 @@ public class CpuState {
         this.nextArgs[1] = s.nextArgs[1];
         this.instSize = s.instSize;
         this.opTrap = s.opTrap;
+        this.nmiAsserted = s.nmiAsserted;
         this.irqAsserted = s.irqAsserted;
         this.carryFlag = s.carryFlag;
         this.negativeFlag = s.negativeFlag;

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

@@ -28,6 +28,7 @@ package com.loomcom.symon;
 import com.loomcom.symon.machines.MulticompMachine;
 import com.loomcom.symon.machines.SimpleMachine;
 import com.loomcom.symon.machines.SymonMachine;
+import com.loomcom.symon.machines.BenEaterMachine;
 import org.apache.commons.cli.*;
 
 import java.util.Locale;
@@ -52,6 +53,7 @@ public class Main {
         options.addOption(new Option("m", "machine", true, "Specify machine type."));
         options.addOption(new Option("c", "cpu", true, "Specify CPU type."));
         options.addOption(new Option("r", "rom", true, "Specify ROM file."));
+        options.addOption(new Option("b", "brk", false, "Halt on BRK"));
 
         CommandLineParser parser = new DefaultParser();
 
@@ -59,6 +61,7 @@ public class Main {
             CommandLine line = parser.parse(options, args);
             InstructionTable.CpuBehavior cpuBehavior = null;
             String romFile = null;
+            boolean haltOnBreak = false;
 
             if (line.hasOption("machine")) {
                 String machine = line.getOptionValue("machine").toLowerCase(Locale.ENGLISH);
@@ -72,6 +75,9 @@ public class Main {
                     case "symon":
                         machineClass = SymonMachine.class;
                         break;
+                    case "beneater":
+                        machineClass = BenEaterMachine.class;
+                        break;
                     default:
                         System.err.println("Could not start Symon. Unknown machine type " + machine);
                         return;
@@ -100,9 +106,13 @@ public class Main {
                 romFile = line.getOptionValue("rom");
             }
 
+            if (line.hasOption("brk")) {
+                haltOnBreak = true;
+            }
+
             while (true) {
                 if (machineClass == null) {
-                    Object[] possibilities = {"Symon", "Multicomp", "Simple"};
+                    Object[] possibilities = {"Symon", "Multicomp", "Simple", "BenEater"};
                     String s = (String)JOptionPane.showInputDialog(
                             null,
                             "Please choose the machine type to be emulated:",
@@ -117,6 +127,8 @@ public class Main {
                         machineClass = MulticompMachine.class;
                     } else if (s != null && s.equals("Simple")) {
                         machineClass = SimpleMachine.class;
+                    } else if (s != null && s.equals("BenEater")) {
+                        machineClass = BenEaterMachine.class;
                     } else {
                         machineClass = SymonMachine.class;
                     }
@@ -126,7 +138,7 @@ public class Main {
                     cpuBehavior = InstructionTable.CpuBehavior.NMOS_6502;
                 }
 
-                final Simulator simulator = new Simulator(machineClass, cpuBehavior, romFile);
+                final Simulator simulator = new Simulator(machineClass, cpuBehavior, romFile, haltOnBreak);
 
                 SwingUtilities.invokeLater(new Runnable() {
                     @Override

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

@@ -29,8 +29,6 @@ public interface Preferences {
 
     int DEFAULT_PROGRAM_LOAD_ADDRESS = 0x0300;
 
-    boolean DEFAULT_HALT_ON_BREAK = true;
-
     JDialog getDialog();
 
     int getProgramStartAddress();

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

@@ -126,6 +126,8 @@ public class Simulator {
 
     private MainCommand command = MainCommand.NONE;
 
+    private boolean haltOnBreak;
+
     public enum MainCommand {
         NONE,
         SELECTMACHINE
@@ -137,16 +139,17 @@ public class Simulator {
     private static final String[] STEPS = {"1", "5", "10", "20", "50", "100"};
 
     public Simulator(Class machineClass) throws Exception {
-        this(machineClass, InstructionTable.CpuBehavior.NMOS_6502, null);
+        this(machineClass, InstructionTable.CpuBehavior.NMOS_6502, null, false);
     }
 
-    public Simulator(Class machineClass, InstructionTable.CpuBehavior cpuType, String romFile) throws Exception {
+    public Simulator(Class machineClass, InstructionTable.CpuBehavior cpuType,
+                     String romFile, boolean haltOnBreak) throws Exception {
+        this.haltOnBreak = haltOnBreak;
         this.breakpoints = new Breakpoints(this);
 
         this.machine = (Machine) machineClass.getConstructors()[0].newInstance(romFile);
         this.machine.getCpu().setBehavior(cpuType);
 
-
         // Initialize final fields in the constructor.
         this.traceLog = new TraceLog();
         this.memoryWindow = new MemoryWindow(machine.getBus());
@@ -176,7 +179,7 @@ public class Simulator {
 
         // File Chooser
         fileChooser = new JFileChooser(System.getProperty("user.dir"));
-        preferences = new PreferencesDialog(mainWindow, true);
+        preferences = new PreferencesDialog(mainWindow, true, haltOnBreak);
 
         // Panel for Console and Buttons
         JPanel consoleContainer = new JPanel();

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

@@ -28,7 +28,7 @@ import com.loomcom.symon.exceptions.MemoryRangeException;
 
 /**
  * This is a simulation of the MOS 6551 ACIA, with limited
- * functionality.  Interrupts are not supported.
+ * functionality.
  * <p/>
  * Unlike a 16550 UART, the 6551 ACIA has only one-byte transmit and
  * receive buffers. It is the programmer's responsibility to check the
@@ -53,6 +53,14 @@ public class Acia6551 extends Acia {
 
     public Acia6551(int address) throws MemoryRangeException {
         super(address, ACIA_SIZE, "ACIA");
+
+        // Figure 6 in the 6551 ACIA data sheet says the "hardware reset"
+        // state of the Control Register is all zeros.
+        setControlRegister(0b00000000);
+        // Figure 7 of the 6551 ACIA data sheet says the "hardware reset"
+        // state of the Command Register is zeros, but Transmitter Control
+        // is set to "interrupt disabled, ready to send".
+        setCommandRegister(0b00000010);
     }
 
     @Override
@@ -74,16 +82,16 @@ public class Acia6551 extends Acia {
     @Override
     public void write(int address, int data) throws MemoryAccessException {
         switch (address) {
-            case 0:
+            case DATA_REG:
                 txWrite(data);
                 break;
-            case 1:
+            case STAT_REG:
                 reset();
                 break;
-            case 2:
+            case CMND_REG:
                 setCommandRegister(data);
                 break;
-            case 3:
+            case CTRL_REG:
                 setControlRegister(data);
                 break;
             default:
@@ -110,67 +118,60 @@ public class Acia6551 extends Acia {
         controlRegister = data;
         int rate = 0;
 
-        // If the value of the data is 0, this is a request to reset,
+        // Mask the lower four bits to get the baud rate.
-        // otherwise it's a control update.
+        int baudSelector = data & 0x0f;
-
+        switch (baudSelector) {
-        if (data == 0) {
+            case 0:
-            reset();
+                rate = 0;
-        } else {
+                break;
-            // Mask the lower three bits to get the baud rate.
+            case 1:
-            int baudSelector = data & 0x0f;
+                rate = 50;
-            switch (baudSelector) {
+                break;
-                case 0:
+            case 2:
-                    rate = 0;
+                rate = 75;
-                    break;
+                break;
-                case 1:
+            case 3:
-                    rate = 50;
+                rate = 110; // Real rate is actually 109.92
-                    break;
+                break;
-                case 2:
+            case 4:
-                    rate = 75;
+                rate = 135; // Real rate is actually 134.58
-                    break;
+                break;
-                case 3:
+            case 5:
-                    rate = 110; // Real rate is actually 109.92
+                rate = 150;
-                    break;
+                break;
-                case 4:
+            case 6:
-                    rate = 135; // Real rate is actually 134.58
+                rate = 300;
-                    break;
+                break;
-                case 5:
+            case 7:
-                    rate = 150;
+                rate = 600;
-                    break;
+                break;
-                case 6:
+            case 8:
-                    rate = 300;
+                rate = 1200;
-                    break;
+                break;
-                case 7:
+            case 9:
-                    rate = 600;
+                rate = 1800;
-                    break;
+                break;
-                case 8:
+            case 10:
-                    rate = 1200;
+                rate = 2400;
-                    break;
+                break;
-                case 9:
+            case 11:
-                    rate = 1800;
+                rate = 3600;
-                    break;
+                break;
-                case 10:
+            case 12:
-                    rate = 2400;
+                rate = 4800;
-                    break;
+                break;
-                case 11:
+            case 13:
-                    rate = 3600;
+                rate = 7200;
-                    break;
+                break;
-                case 12:
+            case 14:
-                    rate = 4800;
+                rate = 9600;
-                    break;
+                break;
-                case 13:
+            case 15:
-                    rate = 7200;
+                rate = 19200;
-                    break;
+                break;
-                case 14:
-                    rate = 9600;
-                    break;
-                case 15:
-                    rate = 19200;
-                    break;
-            }
-
-            setBaudRate(rate);
         }
+
+        setBaudRate(rate);
     }
 
 
@@ -203,13 +204,16 @@ public class Acia6551 extends Acia {
 
 
     private synchronized void reset() {
-        txChar = 0;
+        // Figure 6 in the 6551 ACIA data sheet says the "program reset"
-        txEmpty = true;
+        // event does not modify the control register.
-        rxChar = 0;
-        rxFull = false;
-        receiveIrqEnabled = false;
-        transmitIrqEnabled = false;
-        interrupt = false;
-    }
 
+        // Figure 7 in the 6551 ACIA data sheet says the "program reset"
+        // event keeps the "parity check" configuration in the command
+        // register, but resets the other bits to defaults.
+        setCommandRegister((commandRegister & 0xe0) | 0x02);
+
+        // Figure 8 in the 6551 ACIA data sheet says the "program reset"
+        // event clears the "overrun" flag but otherwise has no effect.
+        overrun = false;
+    }
 }

src/main/java/com/loomcom/symon/jterminal/vt100/Vt100TerminalModel.java

@@ -215,7 +215,8 @@ public class Vt100TerminalModel extends AbstractTerminalModel {
 				case '\t':
 					while ((++cursorColumn % TAB_WIDTH) != 0);
 					continue;
-				case 127:
+				case 8:   // ASCII Backspace
+				case 127: // ASCII Delete
 					if (cursorColumn > 0) {
 						cells[cursorRow][--cursorColumn] = null;
 					}

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

@@ -0,0 +1,169 @@
+/*
+ * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ *                    Maik Merten <maikmerten@googlemail.com>
+ *                    Chelsea Wilkinson <mail@chelseawilkinson.me>
+ *
+ * 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;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.*;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.File;
+
+public class BenEaterMachine implements Machine {
+
+    private final static Logger logger = LoggerFactory.getLogger(BenEaterMachine.class.getName());
+
+    // Constants used by the simulated system. These define the memory map.
+    private static final int BUS_BOTTOM = 0x0000;
+    private static final int BUS_TOP    = 0xffff;
+
+    // 16K of RAM from $0000 - $3FFF
+    private static final int MEMORY_BASE = 0x0000;
+    private static final int MEMORY_SIZE = 0x4000;
+
+    // VIA at $6000-$600F
+    private static final int PIA_BASE = 0x6000;
+
+    // ACIA at $5000-$5003
+    private static final int ACIA_BASE = 0x5000;
+
+    // CRTC at $4000-$4001
+    private static final int CRTC_BASE = 0x4000;
+
+    // 32KB ROM at $8000-$FFFF
+    private static final int ROM_BASE = 0x8000;
+    private static final int ROM_SIZE = 0x8000;
+
+
+        // The simulated peripherals
+    private final Bus    bus;
+    private final Cpu    cpu;
+    private final Acia   acia;
+    private final Pia    pia;
+    private final Crtc   crtc;
+    private final Memory ram;
+    private       Memory rom;
+
+
+    public BenEaterMachine(String romFile) throws Exception {
+        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.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(pia);
+        bus.addDevice(acia);
+        bus.addDevice(crtc);
+
+        if (romFile != null) {
+            File romImage = new File(romFile);
+            if (romImage.canRead()) {
+                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 {} not found, loading empty R/W memory image.", romImage);
+                this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+            }
+        } else {
+            logger.info("No ROM file specified, loading empty R/W memory image.");
+            this.rom = Memory.makeRAM(ROM_BASE, ROM_BASE + ROM_SIZE - 1);
+        }
+
+        bus.addDevice(rom);
+
+    }
+
+    @Override
+    public Bus getBus() {
+        return bus;
+    }
+
+    @Override
+    public Cpu getCpu() {
+        return cpu;
+    }
+
+    @Override
+    public Memory getRam() {
+        return ram;
+    }
+
+    @Override
+    public Acia getAcia() {
+        return acia;
+    }
+
+    @Override
+    public Pia getPia() {
+        return pia;
+    }
+
+    @Override
+    public Crtc getCrtc() {
+        return crtc;
+    }
+
+    @Override
+    public Memory getRom() {
+        return rom;
+    }
+
+    public void setRom(Memory rom) throws MemoryRangeException {
+        if(this.rom != null) {
+            bus.removeDevice(this.rom);
+        }
+        this.rom = rom;
+        bus.addDevice(this.rom);
+    }
+
+    @Override
+    public int getRomBase() {
+        return ROM_BASE;
+    }
+
+    @Override
+    public int getRomSize() {
+        return ROM_SIZE;
+    }
+
+    @Override
+    public int getMemorySize() {
+        return MEMORY_SIZE;
+    }
+
+    @Override
+    public String getName() {
+        return "benEater";
+    }
+
+
+}

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

@@ -42,11 +42,11 @@ public class PreferencesDialog extends Observable implements Preferences {
     private JTextField programLoadAddressField;
 
     private int programLoadAddress = DEFAULT_PROGRAM_LOAD_ADDRESS;
-    private boolean haltOnBreak = DEFAULT_HALT_ON_BREAK;
+    private boolean haltOnBreak;
 
-    public PreferencesDialog(Frame parent, boolean modal) {
+    public PreferencesDialog(Frame parent, boolean modal, boolean haltOnBreak) {
         this.dialog = new JDialog(parent, modal);
-
+        this.haltOnBreak = haltOnBreak;
         createUi();
         updateUi();
     }

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

@@ -30,6 +30,7 @@ import com.loomcom.symon.machines.Machine;
 import javax.swing.*;
 import javax.swing.border.Border;
 import javax.swing.border.EtchedBorder;
+import javax.swing.plaf.metal.MetalTextFieldUI;
 import java.awt.*;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
@@ -69,7 +70,7 @@ public class StatusPanel extends JPanel {
     private JTextField xField;
     private JTextField yField;
 
-    private Machine machine;
+    private final Machine machine;
 
     private static final int EMPTY_BORDER = 10;
     private static final Border LABEL_BORDER = BorderFactory.createEmptyBorder(0, 5, 0, 0);
@@ -392,6 +393,13 @@ public class StatusPanel extends JPanel {
         textField.setMaximumSize(size);
         textField.setPreferredSize(size);
         textField.setBackground(Color.WHITE);
+        // Although we usually defer to the system look-and-feel, for
+        // these small text fields in particular, we use a Metal
+        // look-and-feel because native look-and-feel breaks very small
+        // text fields under GTK+ (they are drawn with an inner margin
+        // even if the margin is set to 0)
+        textField.setUI(new MetalTextFieldUI());
+
         return textField;
     }
 

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

@@ -61,6 +61,7 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
     private static final Logger logger = Logger.getLogger(VideoWindow.class.getName());
 
+    private static final long WINDOW_REPAINT_INTERVAL = 66; // 30fps rate
     private static final int CHAR_WIDTH = 8;
     private static final int CHAR_HEIGHT = 8;
 
@@ -127,6 +128,18 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
                 public void run() {
                     if (cursorBlinkRate > 0) {
                         hideCursor = !hideCursor;
+                    }
+                }
+            });
+        }
+    }
+
+    private class WindowPainter implements Runnable {
+        public void run() {
+            SwingUtilities.invokeLater(new Runnable () {
+                @Override
+                public void run() {
+                    if (VideoWindow.this.isVisible()) {
                         VideoWindow.this.repaint();
                     }
                 }
@@ -152,6 +165,11 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
                                                                TimeUnit.MILLISECONDS);
         }
 
+        scheduler.scheduleAtFixedRate(new WindowPainter(),
+                WINDOW_REPAINT_INTERVAL,
+                WINDOW_REPAINT_INTERVAL,
+                TimeUnit.MILLISECONDS);
+
         // Capture some state from the CRTC that will define the
         // window size. When these values change, the window will
         // need to re-pack and redraw.

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

@@ -254,4 +254,76 @@ public class AciaTest {
 
         assertEquals(0x08, acia.read(0x0001, true));
     }
+
+    @Test
+    public void statusRegisterInitializedAtHardwareReset() throws Exception {
+        Acia6551 acia = new Acia6551(0x0000);
+
+        assertEquals(0x10, acia.read(0x0001, false));
+    }
+
+    @Test
+    public void commandRegisterInitializedAtHardwareReset() throws Exception {
+        Acia6551 acia = new Acia6551(0x0000);
+
+        assertEquals(0x02, acia.read(0x0002, false));
+    }
+
+    @Test
+    public void controlRegisterInitializedAtHardwareReset() throws Exception {
+        Acia6551 acia = new Acia6551(0x0000);
+
+        assertEquals(0x00, acia.read(0x0003, false));
+    }
+
+    @Test
+    public void programResetClearsOverrunStatus() throws Exception {
+        Acia6551 acia = new Acia6551(0x0000);
+        Bus bus = new Bus(acia.ACIA_SIZE);
+        acia.setBus(bus);
+
+        // Change as many status bits as we can.
+        acia.write(0x0002, 0x00); // enable receive interrupt
+        acia.rxWrite('a');
+        acia.rxWrite('b'); // overrun, receive full, interrupt signalled
+        acia.write(0x0000, 'c'); // Transmitter Data Register not empty
+
+        // Check that all the bits we expected to be set actually are
+        assertEquals(0x8C, acia.read(0x0001, false));
+
+        // Do a "program reset". The value is ignored.
+        acia.write(0x0001, 0xFF);
+
+        // Check that only bit 2 was cleared.
+        assertEquals(0x88, acia.read(0x0001, false));
+    }
+
+    @Test
+    public void programResetKeepsParitySettings() throws Exception {
+        Acia6551 acia = new Acia6551(0x0000);
+
+        // Set all the command register bits
+        acia.write(0x0002, 0xFF);
+
+        // Do a "program reset". The value is ignored.
+        acia.write(0x0001, 0xFF);
+
+        // The top 3 bits should be kept as-is,
+        // the bottom 5 bits should be reset to defaults.
+        assertEquals(0xE2, acia.read(0x0002, false));
+    }
+
+    @Test
+    public void programResetLeavesControlRegisterUnchanged() throws Exception {
+        Acia6551 acia = new Acia6551(0x0000);
+
+        // Set all the control register bits
+        acia.write(0x0003, 0xFF);
+
+        // Do a "program reset". The value is ignored.
+        acia.write(0x0001, 0xFF);
+
+        // No bits should have changed.
+        assertEquals(0xFF, acia.read(0x0003, false));
+    }
 }

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

@@ -29,7 +29,7 @@ public class CpuAbsoluteModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*
@@ -169,7 +169,7 @@ public class CpuAbsoluteModeTest extends TestCase {
         assertEquals(0x04, bus.read(0x1fe, true));
 
         // No flags should have changed.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /* BIT - Bit Test - $2c */
@@ -362,7 +362,7 @@ public class CpuAbsoluteModeTest extends TestCase {
         cpu.step();
         assertEquals(0x3400, cpu.getProgramCounter());
         // No change to status flags.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /* EOR - Exclusive OR - $4d */

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

@@ -29,7 +29,7 @@ public class CpuAbsoluteXModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*

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

@@ -29,7 +29,7 @@ public class CpuAbsoluteYModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*

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

@@ -30,7 +30,7 @@ public class CpuAccumulatorModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
    /*
@@ -306,4 +306,4 @@ public class CpuAccumulatorModeTest extends TestCase {
         assertFalse(cpu.getCarryFlag());
     }
 
-}
+}

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

@@ -29,7 +29,7 @@ public class CpuImmediateModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*

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

@@ -33,7 +33,7 @@ public class CpuImpliedModeTest {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*
@@ -76,6 +76,7 @@ public class CpuImpliedModeTest {
     public void test_BRK() throws MemoryAccessException {
         cpu.setCarryFlag();
         cpu.setOverflowFlag();
+        cpu.clearIrqDisableFlag();
         assertEquals(0x20 | Cpu.P_CARRY | Cpu.P_OVERFLOW,
                      cpu.getProcessorStatus());
         assertEquals(0x00, cpu.stackPeek());
@@ -343,7 +344,7 @@ public class CpuImpliedModeTest {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x201, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /* PHA - Push Accumulator - $48 */
@@ -432,7 +433,7 @@ public class CpuImpliedModeTest {
         cpu.step();
 
         assertEquals(0x0f12, cpu.getProgramCounter());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /* SEC - Set Carry Flag - $38 */
@@ -641,4 +642,4 @@ public class CpuImpliedModeTest {
         assertFalse(cpu.getZeroFlag());
         assertTrue(cpu.getNegativeFlag());
     }
-}
+}

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

@@ -31,7 +31,7 @@ public class CpuIndexedIndirectModeTest {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     @Test
@@ -105,4 +105,4 @@ public class CpuIndexedIndirectModeTest {
         assertEquals(0x11, cpu.getAccumulator());
         assertEquals(0x31, bus.read(0xc51f, true));
     }
-}
+}

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

@@ -31,7 +31,7 @@ public class CpuIndirectIndexedModeTest {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     @Test
@@ -81,4 +81,4 @@ public class CpuIndirectIndexedModeTest {
         assertEquals(0xe3, bus.read(0xd828, true));
     }
 
-}
+}

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

@@ -29,7 +29,7 @@ public class CpuIndirectModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*
@@ -48,7 +48,7 @@ public class CpuIndirectModeTest extends TestCase {
         cpu.step();
         assertEquals(0x5400, cpu.getProgramCounter());
         // No change to status flags.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     public void test_JMP_with_ROR_Bug() throws MemoryAccessException {
@@ -60,7 +60,7 @@ public class CpuIndirectModeTest extends TestCase {
         cpu.step();
         assertEquals(0x2200, cpu.getProgramCounter());
         // No change to status flags.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     public void test_JMP_withIndirectBug() throws MemoryAccessException {
@@ -72,7 +72,7 @@ public class CpuIndirectModeTest extends TestCase {
         cpu.step();
         assertEquals(0x2200, cpu.getProgramCounter());
         // No change to status flags.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     public void test_JMP_withOutIndirectBug() throws MemoryAccessException {
@@ -84,7 +84,7 @@ public class CpuIndirectModeTest extends TestCase {
         cpu.step();
         assertEquals(0x5400, cpu.getProgramCounter());
         // No change to status flags.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     public void test_JMP_cmos() throws MemoryAccessException {
@@ -96,7 +96,7 @@ public class CpuIndirectModeTest extends TestCase {
         cpu.step();
         assertEquals(0x5400, cpu.getProgramCounter());
         // No change to status flags.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
-}
+}

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

@@ -28,7 +28,7 @@ public class CpuIndirectXModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*

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

@@ -29,7 +29,7 @@ public class CpuRelativeModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
   /*
@@ -278,4 +278,4 @@ public class CpuRelativeModeTest extends TestCase {
         assertEquals(0x202, cpu.getProgramCounter());
     }
 
-}
+}

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

@@ -44,7 +44,7 @@ public class CpuTest extends TestCase {
         assertEquals(0x0200, cpu.getProgramCounter());
         assertFalse(cpu.getCarryFlag());
         assertFalse(cpu.getZeroFlag());
-        assertFalse(cpu.getIrqDisableFlag());
+        assertTrue(cpu.getIrqDisableFlag());
         assertFalse(cpu.getDecimalModeFlag());
         assertFalse(cpu.getBreakFlag());
         assertFalse(cpu.getOverflowFlag());
@@ -205,14 +205,12 @@ public class CpuTest extends TestCase {
     }
 
     public void testGetProcessorStatus() {
-        // By default, no flags are set.  Remember, bit 5
+        // By default, only "interrupt disable" is set.  Remember, bit 5
         // is always '1'.
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
         cpu.setCarryFlag();
-        assertEquals(0x21, cpu.getProcessorStatus());
+        assertEquals(0x25, cpu.getProcessorStatus());
         cpu.setZeroFlag();
-        assertEquals(0x23, cpu.getProcessorStatus());
-        cpu.setIrqDisableFlag();
         assertEquals(0x27, cpu.getProcessorStatus());
         cpu.setDecimalModeFlag();
         assertEquals(0x2f, cpu.getProcessorStatus());
@@ -237,13 +235,16 @@ public class CpuTest extends TestCase {
         assertEquals(0xa0, cpu.getProcessorStatus());
         cpu.clearNegativeFlag();
         assertEquals(0x20, cpu.getProcessorStatus());
+
+        cpu.setIrqDisableFlag();
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     public void testSetProcessorStatus() {
         // Default
         assertFalse(cpu.getZeroFlag());
         assertFalse(cpu.getZeroFlag());
-        assertFalse(cpu.getIrqDisableFlag());
+        assertTrue(cpu.getIrqDisableFlag());
         assertFalse(cpu.getDecimalModeFlag());
         assertFalse(cpu.getBreakFlag());
         assertFalse(cpu.getOverflowFlag());
@@ -669,4 +670,4 @@ public class CpuTest extends TestCase {
         cpu.step();
         assertEquals(0x3E, cpu.getAccumulator());
     }
-}
+}

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

@@ -29,7 +29,7 @@ public class CpuZeroPageModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*

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

@@ -29,7 +29,7 @@ public class CpuZeroPageXModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*

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

@@ -29,7 +29,7 @@ public class CpuZeroPageYModeTest extends TestCase {
         assertEquals(0, cpu.getYRegister());
         assertEquals(0x200, cpu.getProgramCounter());
         assertEquals(0xff, cpu.getStackPointer());
-        assertEquals(0x20, cpu.getProcessorStatus());
+        assertEquals(0x24, cpu.getProcessorStatus());
     }
 
     /*

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

@@ -8,7 +8,7 @@ import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
-import org.mockito.runners.MockitoJUnitRunner;
+import org.mockito.junit.MockitoJUnitRunner;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;