Update README and pom.xml for release 1.5.0

This change adds a new "Step Over" button, which is enabled
when a "JSR" (Jump to Subroutine) instruction is encountered
while stepping through execution one instruction at a time.

Pressing "Step Over" will continue running instructions until a
corresponding "RTS" (Return from Subroutine) is encountered.
While stepping over a subroutine, the call stack depth is tracked
in an attempt to halt only when the *correct* RTS is encountered.
In other words, it should skip over other subroutines nested
inside the call you want to step over:

```
     JSR A # Step over here...
     ...
     JSR B
     ...
     RTS   # Returns from 'B', doesn't halt
     ...
     RTS   # Returns from 'A', halts after return
```

Implements feature request #18.

README.md

@@ -1,9 +1,9 @@
 SYMON - A 6502 System Simulator
 ===============================
 
-**Version:** 1.3.2
+**Version:** 1.5.0
 
-**Last Updated:** 08 March, 2021
+**Last Updated:** 30 March, 2025
 
 See the file COPYING for license.
 
@@ -25,20 +25,20 @@ Klaus Dormann's 6502 Functional Test Suite as of version 0.8.2
 (See [this thread on the 6502.org Forums](http://forum.6502.org/viewtopic.php?f=2&t=2241)
 for more information about this functional test suite).
 
-Symon is under constant, active development. Feedback and patches
+Symon is under active maintenance. Feedback and patches are always
-are always welcome.
+welcome.
 
 ## 2.0 Requirements
 
-  - Java 1.8 or higher
+  - Java 10 or higher
-  - Maven 2.0.x or higher (for building from source)
+  - Maven 3.0.x or higher (for building from source)
   - JUnit 4 or higher (for testing)
 
 ## 3.0 Features
 
 Symon can simulate multiple 6502 based architectures. At present, four
-machines are implemented: Symon (the default), MULTICOMP, BenEater, and a "Simple"
+machines are implemented: Symon (the default), MULTICOMP, BenEater, and
-machine useful for debugging.
+a "Simple" machine useful for debugging.
 
 ### 3.1 Memory Maps
 
@@ -270,6 +270,17 @@ running.
 
 ## 5.0 Revision History
 
+  - **1.5.0:** 30 March 2025 - Fixed a bug that caused some 6502
+    instructions to be disassembled improperly in the trace log
+    (GitHub issue #17).
+
+    Added a new "Step Over" button that allows stepping over the
+    current subroutine. This button only becomes active when the
+    next instruction is a "JSR" while stepping through execution 
+    one instruction at a time. It will continue execution until
+    the subroutine returns through a corresponding "RTS" instruction.
+    (GitHub feature request #18).
+
   - **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
@@ -355,17 +366,12 @@ running.
 
   - Feedback (in the form of dialogs, status bar, etc).
 
-  - Better debugging tools from the UI, including breakpoints
-    and disassembly.
-
   - UI needs a ton more polish.
 
   - More extensive testing.
 
   - Clean up JavaDoc.
 
-  - Implement CMOS 65C02 instructions and NMOS / CMOS mode flag.
-
   - Allow displaying ACIA status and dumping ACIA buffers, for
     debugging.
 
@@ -375,13 +381,19 @@ running.
 
   - Symbolic debugging.
 
+  - Better / correct disassembly and tracing of 65C02 and 65C816
+    instructions.
+
 ## 8.0 Copyright and Acknowledgements
 
-**Copyright (c) 2014 Seth J. Morabito <web@loomcom.com>**
+**Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>**
 
-Portions Copyright (c) 2014 Maik Merten <maikmerten@googlemail.com>
+  - Portions Copyright (c) 2014 Maik Merten 
-Portions Copyright (c) 2022 Tim Allen <thristian@gmail.com>
+    <maikmerten@googlemail.com>
-Portions Copyright (c) 2023 Chelsea Wilkinson <mail@chelseawilkinson.me>
+  - Portions Copyright (c) 2022 Tim Allen 
+    <thristian@gmail.com>
+  - Portions Copyright (c) 2023 Chelsea Wilkinson 
+    <mail@chelseawilkinson.me>
 
 Additional components used in this project are copyright their respective owners.
 

pom.xml

@@ -1,12 +1,12 @@
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/maven-v4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.loomcom.symon</groupId>
     <artifactId>symon</artifactId>
     <packaging>jar</packaging>
-    <version>1.4.0</version>
+    <version>1.5.0</version>
     <name>symon</name>
-    <url>http://www.loomcom.com/symon</url>
+    <url>https://git.loomcom.com/seth/symon</url>
     <properties>
         <project.build.sourceEncoding>
             UTF-8
@@ -19,7 +19,7 @@
         <dependency>
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-classic</artifactId>
-            <version>1.4.5</version>
+            <version>1.5.16</version>
         </dependency>
         <dependency>
             <groupId>junit</groupId>
@@ -30,7 +30,7 @@
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>
-            <version>4.8.0</version>
+            <version>4.11.0</version>
             <scope>test</scope>
         </dependency>
         <dependency>

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

@@ -1,3 +1,26 @@
+/*
+ * Copyright (c) 2008-2025 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;
 
 import com.loomcom.symon.exceptions.MemoryAccessException;
@@ -9,8 +32,8 @@ import java.util.TreeSet;
 
 public class Breakpoints extends AbstractTableModel {
 
-    private TreeSet<Integer> breakpoints;
+    private final TreeSet<Integer> breakpoints;
-    private Simulator simulator;
+    private final Simulator simulator;
 
     public Breakpoints(Simulator simulator) {
         this.breakpoints = new TreeSet<>();
@@ -26,11 +49,6 @@ public class Breakpoints extends AbstractTableModel {
         fireTableDataChanged();
     }
 
-    public void removeBreakpoint(int address) {
-        this.breakpoints.remove(address);
-        fireTableDataChanged();
-    }
-
     public void removeBreakpointAtIndex(int index) {
         if (index < 0) {
             return;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -42,19 +42,19 @@ import java.util.TreeSet;
 public class Bus {
 
     // The default address at which to load programs
-    public static int DEFAULT_LOAD_ADDRESS = 0x0200;
+    public static final int DEFAULT_LOAD_ADDRESS = 0x0200;
 
     // By default, our bus starts at 0, and goes up to 64K
-    private int startAddress = 0x0000;
+    private final int startAddress;
-    private int endAddress = 0xffff;
+    private final int endAddress;
 
     // The CPU
     private Cpu cpu;
 
     // Ordered sets of IO devices, associated with their priority
-    private Map<Integer, SortedSet<Device>> deviceMap;
+    private final Map<Integer, SortedSet<Device>> deviceMap;
 
-    // an array for quick lookup of adresses, brute-force style
+    // an array for quick lookup of addresses, brute-force style
     private Device[] deviceAddressArray;
 
 
@@ -94,8 +94,8 @@ public class Bus {
      * Add a device to the bus.
      *
      * @param device   Device to add
-     * @param priority Bus prioirity.
+     * @param priority Bus priority.
-     * @throws MemoryRangeException
+     * @throws MemoryRangeException Invalid device address range.
      */
     public void addDevice(Device device, int priority) throws MemoryRangeException {
 
@@ -109,12 +109,7 @@ public class Bus {
             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);
+        SortedSet<Device> deviceSet = deviceMap.computeIfAbsent(priority, k -> new TreeSet<>());
-
-        if (deviceSet == null) {
-            deviceSet = new TreeSet<>();
-            deviceMap.put(priority, deviceSet);
-        }
 
         device.setBus(this);
         deviceSet.add(device);
@@ -125,7 +120,7 @@ public class Bus {
      * Add a device to the bus. Throws a MemoryRangeException if the device overlaps with any others.
      *
      * @param device Device to add
-     * @throws MemoryRangeException
+     * @throws MemoryRangeException Invalid device memory range.
      */
     public void addDevice(Device device) throws MemoryRangeException {
         addDevice(device, 0);
@@ -224,9 +219,7 @@ public class Bus {
 
         for (int priority : priorities) {
             SortedSet<Device> deviceSet = deviceMap.get(priority);
-            for (Device device : deviceSet) {
+            devices.addAll(deviceSet);
-                devices.add(device);
-            }
         }
 
         return devices;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -158,6 +158,8 @@ public class Cpu implements InstructionTable {
      * Performs an individual instruction cycle.
      */
     public void step() throws MemoryAccessException {
+        int hi, lo; // Address calculation
+
         opBeginTime = System.nanoTime();
 
         // Store the address from which the IR was read, for debugging
@@ -317,8 +319,8 @@ public class Cpu implements InstructionTable {
                 break;
             case 0x40: // RTI - Return from Interrupt - Implied
                 setProcessorStatus(stackPop());
-                int lo = stackPop();
+                lo = stackPop();
-                int hi = stackPop();
+                hi = stackPop();
                 setProgramCounter(Utils.address(lo, hi));
                 break;
             case 0x48: // PHA - Push Accumulator - Implied
@@ -1697,6 +1699,10 @@ public class Cpu implements InstructionTable {
         return state.ir;
     }
 
+    public int getNextIr() {
+        return state.nextIr;
+    }
+
     /**
      * @value The value of the Process Status Register bits to be set.
      */
@@ -1923,6 +1929,7 @@ public class Cpu implements InstructionTable {
                 break;
             case AIX:
                 sb.append(" ($").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(",X)");
+                break;
             case ABX:
                 sb.append(" $").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(",X");
                 break;
@@ -1935,6 +1942,9 @@ public class Cpu implements InstructionTable {
             case IND:
                 sb.append(" ($").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(")");
                 break;
+            case ZPI:
+                sb.append(" ($").append(Utils.byteToHex(args[0])).append(")");
+                break;
             case XIN:
                 sb.append(" ($").append(Utils.byteToHex(args[0])).append(",X)");
                 break;

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

@@ -1,3 +1,26 @@
+/*
+ * Copyright (c) 2008-2025 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;
 
 import com.loomcom.symon.util.Utils;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -25,26 +25,24 @@ package com.loomcom.symon;
 
 public interface InstructionTable {
 
+    int BRK = 0x00;
+    int JSR = 0x20;
+    int RTS = 0x60;
+
     /**
      * Enumeration of valid CPU behaviors. These determine what behavior and instruction
      * set will be simulated, depending on desired version of 6502.
-     *
-     * TODO: As of version 0.6, this is still not used! All CPUs are "idealized" NMOS 6502 only.
      */
     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
          * is very rare in the wild.
-         *
-         * NB: Does NOT implement "unimplemented" NMOS instructions.
          */
         NMOS_WITH_ROR_BUG,
 
         /**
          * All NMOS 6502's have a bug with the indirect JMP instruction. If the
-         *
-         * NB: Does NOT implement "unimplemented" NMOS instructions.
          */
         NMOS_6502,
 
@@ -68,11 +66,13 @@ public interface InstructionTable {
                 return "Accumulator";
             }
         },
+
         AIX {
             public String toString() {
                 return "Absolute, X-Indexed Indirect";
             }
         },
+
         ABS {
             public String toString() {
                 return "Absolute";
@@ -168,41 +168,44 @@ public interface InstructionTable {
 
     /**
      * Instruction opcode names. This lists all opcodes for
-     * NMOS 6502, CMOS 65C02, and CMOS 65C816
+     * NMOS 6502, CMOS 65C02, and CMOS 65C816.
+     * <p>
+     * TODO (2025-03-14): This table is clearly wrong for 65C816.
+     * TODO (2025-03-14): Rockwell/WDC 65C02 names conflict with 65C816 names.
      */
     String[] opcodeNames = {
-        "BRK", "ORA", "NOP", "NOP", "TSB", "ORA", "ASL",  "RMB0",  // 0x00-0x07
+        "BRK", "ORA", "NOP", "NOP", "TSB", "ORA", "ASL", "RMB0",  // 0x00-0x07
-        "PHP", "ORA", "ASL", "NOP", "TSB", "ORA", "ASL",  "BBR0",  // 0x08-0x0f
+        "PHP", "ORA", "ASL", "NOP", "TSB", "ORA", "ASL", "BBR0",  // 0x08-0x0f
-        "BPL", "ORA", "ORA", "NOP", "TRB", "ORA", "ASL",  "RMB1",  // 0x10-0x17
+        "BPL", "ORA", "ORA", "NOP", "TRB", "ORA", "ASL", "RMB1",  // 0x10-0x17
-        "CLC", "ORA", "INC", "NOP", "TRB", "ORA", "ASL",  "BBR1",  // 0x18-0x1f
+        "CLC", "ORA", "INC", "NOP", "TRB", "ORA", "ASL", "BBR1",  // 0x18-0x1f
-        "JSR", "AND", "NOP", "NOP", "BIT", "AND", "ROL",  "RMB2",  // 0x20-0x27
+        "JSR", "AND", "NOP", "NOP", "BIT", "AND", "ROL", "RMB2",  // 0x20-0x27
-        "PLP", "AND", "ROL", "NOP", "BIT", "AND", "ROL",  "BBR2",  // 0x28-0x2f
+        "PLP", "AND", "ROL", "NOP", "BIT", "AND", "ROL", "BBR2",  // 0x28-0x2f
-        "BMI", "AND", "AND", "NOP", "BIT", "AND", "ROL",  "RMB3",  // 0x30-0x37
+        "BMI", "AND", "AND", "NOP", "BIT", "AND", "ROL", "RMB3",  // 0x30-0x37
-        "SEC", "AND", "DEC", "NOP", "BIT", "AND", "ROL",  "BBR3",  // 0x38-0x3f
+        "SEC", "AND", "DEC", "NOP", "BIT", "AND", "ROL", "BBR3",  // 0x38-0x3f
-        "RTI", "EOR", "NOP", "NOP", "NOP", "EOR", "LSR",  "RMB4",  // 0x40-0x47
+        "RTI", "EOR", "NOP", "NOP", "NOP", "EOR", "LSR", "RMB4",  // 0x40-0x47
-        "PHA", "EOR", "LSR", "NOP", "JMP", "EOR", "LSR",  "BBR4",  // 0x48-0x4f
+        "PHA", "EOR", "LSR", "NOP", "JMP", "EOR", "LSR", "BBR4",  // 0x48-0x4f
-        "BVC", "EOR", "EOR", "NOP", "NOP", "EOR", "LSR",  "RMB5",  // 0x50-0x57
+        "BVC", "EOR", "EOR", "NOP", "NOP", "EOR", "LSR", "RMB5",  // 0x50-0x57
-        "CLI", "EOR", "PHY", "NOP", "NOP", "EOR", "LSR",  "BBR5",  // 0x58-0x5f
+        "CLI", "EOR", "PHY", "NOP", "NOP", "EOR", "LSR", "BBR5",  // 0x58-0x5f
-        "RTS", "ADC", "NOP", "NOP", "STZ", "ADC", "ROR",  "RMB6",  // 0x60-0x67
+        "RTS", "ADC", "NOP", "NOP", "STZ", "ADC", "ROR", "RMB6",  // 0x60-0x67
-        "PLA", "ADC", "ROR", "NOP", "JMP", "ADC", "ROR",  "BBR6",  // 0x68-0x6f
+        "PLA", "ADC", "ROR", "NOP", "JMP", "ADC", "ROR", "BBR6",  // 0x68-0x6f
-        "BVS", "ADC", "ADC", "NOP", "STZ", "ADC", "ROR",  "RMB7",  // 0x70-0x77
+        "BVS", "ADC", "ADC", "NOP", "STZ", "ADC", "ROR", "RMB7",  // 0x70-0x77
-        "SEI", "ADC", "PLY", "NOP", "JMP", "ADC", "ROR",  "BBR7",  // 0x78-0x7f
+        "SEI", "ADC", "PLY", "NOP", "JMP", "ADC", "ROR", "BBR7",  // 0x78-0x7f
-        "BRA", "STA", "NOP", "NOP", "STY", "STA", "STX",  "SMB0",  // 0x80-0x87
+        "BRA", "STA", "NOP", "NOP", "STY", "STA", "STX", "SMB0",  // 0x80-0x87
-        "DEY", "BIT", "TXA", "NOP", "STY", "STA", "STX",  "BBS0",  // 0x88-0x8f
+        "DEY", "BIT", "TXA", "NOP", "STY", "STA", "STX", "BBS0",  // 0x88-0x8f
-        "BCC", "STA", "STA", "NOP", "STY", "STA", "STX",  "SMB1",  // 0x90-0x97
+        "BCC", "STA", "STA", "NOP", "STY", "STA", "STX", "SMB1",  // 0x90-0x97
-        "TYA", "STA", "TXS", "NOP", "STZ", "STA", "STZ",  "BBS1",  // 0x98-0x9f
+        "TYA", "STA", "TXS", "NOP", "STZ", "STA", "STZ", "BBS1",  // 0x98-0x9f
-        "LDY", "LDA", "LDX", "NOP", "LDY", "LDA", "LDX",  "SMB2",  // 0xa0-0xa7
+        "LDY", "LDA", "LDX", "NOP", "LDY", "LDA", "LDX", "SMB2",  // 0xa0-0xa7
-        "TAY", "LDA", "TAX", "NOP", "LDY", "LDA", "LDX",  "BBS2",  // 0xa8-0xaf
+        "TAY", "LDA", "TAX", "NOP", "LDY", "LDA", "LDX", "BBS2",  // 0xa8-0xaf
-        "BCS", "LDA", "LDA", "NOP", "LDY", "LDA", "LDX",  "SMB3",  // 0xb0-0xb7
+        "BCS", "LDA", "LDA", "NOP", "LDY", "LDA", "LDX", "SMB3",  // 0xb0-0xb7
-        "CLV", "LDA", "TSX", "NOP", "LDY", "LDA", "LDX",  "BBS3",  // 0xb8-0xbf
+        "CLV", "LDA", "TSX", "NOP", "LDY", "LDA", "LDX", "BBS3",  // 0xb8-0xbf
-        "CPY", "CMP", "NOP", "NOP", "CPY", "CMP", "DEC",  "SMB4",  // 0xc0-0xc7
+        "CPY", "CMP", "NOP", "NOP", "CPY", "CMP", "DEC", "SMB4",  // 0xc0-0xc7
-        "INY", "CMP", "DEX", "NOP", "CPY", "CMP", "DEC",  "BBS4",  // 0xc8-0xcf
+        "INY", "CMP", "DEX", "NOP", "CPY", "CMP", "DEC", "BBS4",  // 0xc8-0xcf
-        "BNE", "CMP", "CMP", "NOP", "NOP", "CMP", "DEC",  "SMB5",  // 0xd0-0xd7
+        "BNE", "CMP", "CMP", "NOP", "NOP", "CMP", "DEC", "SMB5",  // 0xd0-0xd7
-        "CLD", "CMP", "PHX", "NOP", "NOP", "CMP", "DEC",  "BBS5",  // 0xd8-0xdf
+        "CLD", "CMP", "PHX", "NOP", "NOP", "CMP", "DEC", "BBS5",  // 0xd8-0xdf
-        "CPX", "SBC", "NOP", "NOP", "CPX", "SBC", "INC",  "SMB6",  // 0xe0-0xe7
+        "CPX", "SBC", "NOP", "NOP", "CPX", "SBC", "INC", "SMB6",  // 0xe0-0xe7
-        "INX", "SBC", "NOP", "NOP", "CPX", "SBC", "INC",  "BBS6",  // 0xe8-0xef
+        "INX", "SBC", "NOP", "NOP", "CPX", "SBC", "INC", "BBS6",  // 0xe8-0xef
-        "BEQ", "SBC", "SBC", "NOP", "NOP", "SBC", "INC",  "SMB7",  // 0xf0-0xf7
+        "BEQ", "SBC", "SBC", "NOP", "NOP", "SBC", "INC", "SMB7",  // 0xf0-0xf7
-        "SED", "SBC", "PLX", "NOP", "NOP", "SBC", "INC",  "BBS7"   // 0xf8-0xff
+        "SED", "SBC", "PLX", "NOP", "NOP", "SBC", "INC", "BBS7"   // 0xf8-0xff
     };
 
     /**

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

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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
@@ -22,14 +22,12 @@
  * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
-
 package com.loomcom.symon;
 
-import com.loomcom.symon.machines.MulticompMachine;
+import com.loomcom.symon.machines.*;
-import com.loomcom.symon.machines.SimpleMachine;
-import com.loomcom.symon.machines.SymonMachine;
-import com.loomcom.symon.machines.BenEaterMachine;
 import org.apache.commons.cli.*;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.util.Locale;
 import javax.swing.JOptionPane;
@@ -37,6 +35,7 @@ import javax.swing.SwingUtilities;
 import javax.swing.UIManager;
 
 public class Main {
+    private final static Logger logger = LoggerFactory.getLogger(Main.class.getName());
 
      /**
      * Main entry point to the simulator. Creates a simulator and shows the main
@@ -46,7 +45,7 @@ public class Main {
      */
     public static void main(String[] args) throws Exception {
 
-        Class machineClass = SymonMachine.class;
+        Class<?> machineClass = null;
 
         Options options = new Options();
 
@@ -79,7 +78,7 @@ public class Main {
                         machineClass = BenEaterMachine.class;
                         break;
                     default:
-                        System.err.println("Could not start Symon. Unknown machine type " + machine);
+                        logger.error("Could not start Symon. Unknown machine type {}", machine);
                         return;
                 }
             }
@@ -97,7 +96,7 @@ public class Main {
                         cpuBehavior = InstructionTable.CpuBehavior.CMOS_65816;
                         break;
                     default:
-                        System.err.println("Could not start Symon. Unknown cpu type " + cpu);
+                        logger.error("Could not start Symon. Unknown cpu type {}", cpu);
                         return;
                 }
             }
@@ -140,16 +139,14 @@ public class Main {
 
                 final Simulator simulator = new Simulator(machineClass, cpuBehavior, romFile, haltOnBreak);
 
-                SwingUtilities.invokeLater(new Runnable() {
+                SwingUtilities.invokeLater(() -> {
-                    @Override
+                    try {
-                    public void run() {
+                        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
-                        try {
+                        // Create the main UI window
-                            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
+                        simulator.createAndShowUi();
-                            // Create the main UI window
+                    } catch (Exception e) {
-                            simulator.createAndShowUi();
+                        logger.error("Error during Symon UI initialization: {}", e.getMessage());
-                        } catch (Exception e) {
+                        System.exit(-1);
-                            e.printStackTrace();
-                        }
                     }
                 });
 
@@ -163,7 +160,7 @@ public class Main {
                 }
             }
         } catch (ParseException ex) {
-            System.err.println("Could not start Symon. Reason: " + ex.getMessage());
+            logger.error("Could not start Symon. Reason: {}", ex.getMessage());
         }
     }
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -27,7 +27,7 @@ import com.loomcom.symon.exceptions.*;
 
 /**
  * MemoryRange is a simple container class representing a literal
- * range of memory, with a staraddress, and an end address.  It has
+ * range of memory, with a start address, and an end address.  It has
  * guards against creating impossible memory ranges, and implements
  * some useful methods for checking address inclusion and range
  * overlaps.

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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/Simulator.java

@@ -1,5 +1,5 @@
 /*
- * Copyrighi (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -31,14 +31,13 @@ import com.loomcom.symon.ui.Console;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import javax.management.monitor.CounterMonitor;
 import javax.swing.*;
 import javax.swing.border.EmptyBorder;
 import java.awt.*;
 import java.awt.event.*;
 import java.io.*;
-import java.util.SortedSet;
+
-import java.util.TreeSet;
+import static com.loomcom.symon.InstructionTable.*;
 
 /**
  * Symon Simulator Interface and Control.
@@ -72,7 +71,7 @@ public class Simulator {
     private static final int MAX_STEPS_BETWEEN_UPDATES = 20000;
 
     // The simulated machine
-    private Machine machine;
+    private final Machine machine;
 
     // Number of CPU steps between CRT repaints.
     // TODO: Dynamically refresh the value at runtime based on performance figures to reach ~ 30fps.
@@ -115,18 +114,19 @@ public class Simulator {
 
     private JButton runStopButton;
     private JButton stepButton;
+    private JButton stepOverButton;
     private JComboBox<String> stepCountBox;
 
     private JFileChooser fileChooser;
     private PreferencesDialog preferences;
 
-    private Breakpoints breakpoints;
+    private final Breakpoints breakpoints;
 
     private final Object commandMonitorObject = new Object();
 
     private MainCommand command = MainCommand.NONE;
 
-    private boolean haltOnBreak;
+    private final boolean haltOnBreak;
 
     public enum MainCommand {
         NONE,
@@ -138,11 +138,11 @@ public class Simulator {
      */
     private static final String[] STEPS = {"1", "5", "10", "20", "50", "100"};
 
-    public Simulator(Class machineClass) throws Exception {
+    public Simulator(Class<?> machineClass) throws Exception {
         this(machineClass, InstructionTable.CpuBehavior.NMOS_6502, null, false);
     }
 
-    public Simulator(Class machineClass, InstructionTable.CpuBehavior cpuType,
+    public Simulator(Class<?> machineClass, InstructionTable.CpuBehavior cpuType,
                      String romFile, boolean haltOnBreak) throws Exception {
         this.haltOnBreak = haltOnBreak;
         this.breakpoints = new Breakpoints(this);
@@ -165,7 +165,7 @@ public class Simulator {
     /**
      * Display the main simulator UI.
      */
-    public void createAndShowUi() throws IOException {
+    public void createAndShowUi() {
         mainWindow = new JFrame();
         mainWindow.setTitle("6502 Simulator - " + machine.getName());
         mainWindow.setResizable(false);
@@ -191,18 +191,22 @@ public class Simulator {
 
         runStopButton = new JButton("Run");
         stepButton = new JButton("Step");
+        stepOverButton = new JButton("Step Over");
+        stepOverButton.setEnabled(false);
         JButton softResetButton = new JButton("Soft Reset");
         JButton hardResetButton = new JButton("Hard Reset");
 
         stepCountBox = new JComboBox<>(STEPS);
-        stepCountBox.addActionListener(new ActionListener() {
+        stepCountBox.addActionListener(actionEvent -> {
-            @Override
+            JComboBox<?> cb = (JComboBox<?>) actionEvent.getSource();
-            public void actionPerformed(ActionEvent actionEvent) {
+            String cbStepsPerClick = (String) cb.getSelectedItem();
+
+            stepsPerClick = 1; // Default in case of error
+
+            if (cbStepsPerClick != null) {
                 try {
-                    JComboBox cb = (JComboBox) actionEvent.getSource();
+                    stepsPerClick = Integer.parseInt(cbStepsPerClick);
-                    stepsPerClick = Integer.parseInt((String) cb.getSelectedItem());
                 } catch (NumberFormatException ex) {
-                    stepsPerClick = 1;
                     stepCountBox.setSelectedIndex(0);
                 }
             }
@@ -210,6 +214,7 @@ public class Simulator {
 
         buttonContainer.add(runStopButton);
         buttonContainer.add(stepButton);
+        buttonContainer.add(stepOverButton);
         buttonContainer.add(stepCountBox);
         buttonContainer.add(softResetButton);
         buttonContainer.add(hardResetButton);
@@ -224,38 +229,25 @@ public class Simulator {
         // Bottom - buttons.
         mainWindow.getContentPane().add(buttonContainer, BorderLayout.PAGE_END);
 
-        runStopButton.addActionListener(new ActionListener() {
+        runStopButton.addActionListener(actionEvent -> {
-            @Override
+            if (runLoop != null && runLoop.isRunning()) {
-            public void actionPerformed(ActionEvent actionEvent) {
+                Simulator.this.handleStop();
-                if (runLoop != null && runLoop.isRunning()) {
+            } else {
-                    Simulator.this.handleStop();
+                Simulator.this.handleStart();
-                } else {
-                    Simulator.this.handleStart();
-                }
             }
         });
 
-        stepButton.addActionListener(new ActionListener() {
+        stepButton.addActionListener(actionEvent -> Simulator.this.handleStep(stepsPerClick));
-            @Override
+        stepOverButton.addActionListener(actionEvent -> Simulator.this.handleStepOver());
-            public void actionPerformed(ActionEvent actionEvent) {
+
-                Simulator.this.handleStep(stepsPerClick);
+        softResetButton.addActionListener(actionEvent -> {
-            }
+            // If this was a CTRL-click, do a hard reset.
+            Simulator.this.handleReset(false);
         });
 
-        softResetButton.addActionListener(new ActionListener() {
+        hardResetButton.addActionListener(actionEvent -> {
-            @Override
+            // If this was a CTRL-click, do a hard reset.
-            public void actionPerformed(ActionEvent actionEvent) {
+            Simulator.this.handleReset(true);
-                // If this was a CTRL-click, do a hard reset.
-                Simulator.this.handleReset(false);
-            }
-        });
-
-        hardResetButton.addActionListener(new ActionListener() {
-            @Override
-            public void actionPerformed(ActionEvent actionEvent) {
-                // If this was a CTRL-click, do a hard reset.
-                Simulator.this.handleReset(true);
-            }
         });
 
         mainWindow.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
@@ -277,7 +269,7 @@ public class Simulator {
             try {
                 commandMonitorObject.wait();
             } catch (InterruptedException ex) {
-                ex.printStackTrace();
+                logger.error("Interrupted during wait on command monitor.");
             }
         }
         return command;
@@ -340,12 +332,28 @@ public class Simulator {
                 step();
             }
             updateVisibleState();
+            stepOverButton.setEnabled(machine.getCpu().getNextIr() == JSR);
         } catch (SymonException ex) {
             logger.error("Exception during simulator step", ex);
-            ex.printStackTrace();
         }
     }
 
+    /**
+     * Step over a JSR / RTS function. This function is much more like a "run()"
+     * than a "step()", and may enter an infinite loop if no RTS is encountered.
+     */
+    private void handleStepOver() {
+        if (runLoop != null && runLoop.isRunning()) {
+            // This should really never happen...
+            logger.error("Can't step over when the simulator is already running!");
+            return;
+        }
+
+        runLoop = new RunLoop();
+        runLoop.haltOnRts(true);
+        runLoop.start();
+    }
+
     /**
      * Perform a single step of the simulated system.
      */
@@ -365,7 +373,7 @@ public class Simulator {
         // If a key has been pressed, fill the ACIA.
         try {
             if (machine.getAcia() != null && console.hasInput()) {
-                machine.getAcia().rxWrite((int) console.readInputChar());
+                machine.getAcia().rxWrite(console.readInputChar());
             }
         } catch (FifoUnderrunException ex) {
             logger.error("Console type-ahead buffer underrun!");
@@ -414,53 +422,73 @@ public class Simulator {
      */
     class RunLoop extends Thread {
         private boolean isRunning = false;
+        private boolean haltOnRts = false;
+        // The number of JSR instructions we've seen since being asked to
+        // step over a subroutine. While stepping over, this is incremented
+        // on RTS instructions, and decremented on JSR instructions.
+        private int callStackDepth = 0;
 
         public boolean isRunning() {
-            return isRunning;
+            return this.isRunning;
         }
 
         public void requestStop() {
-            isRunning = false;
+            this.isRunning = false;
+        }
+
+        public void haltOnRts(boolean value) {
+            this.haltOnRts = value;
         }
 
         public void run() {
-            logger.debug("Starting main run loop.");
+            if (this.haltOnRts) {
-            isRunning = true;
+                logger.debug("Running until next RTS instruction");
+            } else {
+                logger.debug("Running");
+            }
+            this.isRunning = true;
 
-            SwingUtilities.invokeLater(new Runnable() {
+            SwingUtilities.invokeLater(() -> {
-                @Override
+                // Don't allow step while the simulator is running
-                public void run() {
+                stepButton.setEnabled(false);
-                    // Don't allow step while the simulator is running
+                stepOverButton.setEnabled(false);
-                    stepButton.setEnabled(false);
+                stepCountBox.setEnabled(false);
-                    stepCountBox.setEnabled(false);
+                menuBar.simulatorDidStart();
-                    menuBar.simulatorDidStart();
+                // Toggle the state of the run button
-                    // Toggle the state of the run button
+                runStopButton.setText("Stop");
-                    runStopButton.setText("Stop");
-                }
             });
 
             try {
                 do {
                     step();
+                    if (this.haltOnRts) {
+                        var instruction = machine.getCpu().getInstruction();
+                        if (instruction == JSR) {
+                            this.callStackDepth++;
+                            logger.trace("Step-over call stack increased to {}", this.callStackDepth);
+                        } else if (this.callStackDepth > 0 && instruction == RTS) {
+                            this.callStackDepth--;
+                            logger.trace("Step-over call stack decreased to {}", this.callStackDepth);
+                        }
+                    }
+
                 } while (shouldContinue());
             } catch (SymonException ex) {
                 logger.error("Exception in main simulator run thread. Exiting run.", ex);
             }
 
-            SwingUtilities.invokeLater(new Runnable() {
+            SwingUtilities.invokeLater(() -> {
-                @Override
+                statusPane.updateState();
-                public void run() {
+                memoryWindow.updateState();
-                    statusPane.updateState();
+                runStopButton.setText("Run");
-                    memoryWindow.updateState();
+                stepButton.setEnabled(true);
-                    runStopButton.setText("Run");
+                stepOverButton.setEnabled(machine.getCpu().getNextIr() == JSR);
-                    stepButton.setEnabled(true);
+                stepCountBox.setEnabled(true);
-                    stepCountBox.setEnabled(true);
+                if (traceLog.isVisible()) {
-                    if (traceLog.isVisible()) {
+                    traceLog.refresh();
-                        traceLog.refresh();
-                    }
-                    menuBar.simulatorDidStop();
-                    traceLog.simulatorDidStop();
                 }
+                menuBar.simulatorDidStop();
+                traceLog.simulatorDidStop();
             });
 
             isRunning = false;
@@ -470,9 +498,13 @@ public class Simulator {
          * @return True if the run loop should proceed to the next step.
          */
         private boolean shouldContinue() {
-            return !breakpoints.contains(machine.getCpu().getProgramCounter()) &&
+            var instruction = machine.getCpu().getInstruction();
-                    isRunning &&
+
-                    !(preferences.getHaltOnBreak() && machine.getCpu().getInstruction() == 0x00);
+            var stepOverHalt = this.haltOnRts && this.callStackDepth == 0 && instruction == RTS;
+            var breakpointHalt = breakpoints.contains(machine.getCpu().getProgramCounter());
+            var brkHalt = preferences.getHaltOnBreak() && instruction == BRK;
+
+            return isRunning && !(stepOverHalt || breakpointHalt || brkHalt);
         }
     }
 
@@ -513,12 +545,9 @@ public class Simulator {
                             // Now load the program at the starting address.
                             loadProgram(program, preferences.getProgramStartAddress());
 
-                            SwingUtilities.invokeLater(new Runnable() {
+                            SwingUtilities.invokeLater(() -> {
-                                @Override
+                                console.reset();
-                                public void run() {
+                                breakpoints.refresh();
-                                    console.reset();
-                                    breakpoints.refresh();
-                                }
                             });
 
                             // TODO: "Don't Show Again" checkbox
@@ -556,7 +585,7 @@ public class Simulator {
                         long fileSize = romFile.length();
 
                         if (fileSize != machine.getRomSize()) {
-                            throw new IOException("ROM file must be exactly " + String.valueOf(machine.getRomSize()) + " bytes.");
+                            throw new IOException("ROM file must be exactly " + machine.getRomSize() + " bytes.");
                         }
 
                         // Load the new ROM image
@@ -650,30 +679,27 @@ public class Simulator {
     }
 
     class SetFontAction extends AbstractAction {
-        private int size;
+        private final int size;
 
         public SetFontAction(int size) {
-            super(Integer.toString(size) + " pt", null);
+            super(size + " pt", null);
             this.size = size;
             putValue(SHORT_DESCRIPTION, "Set font to " + size + "pt.");
         }
 
         public void actionPerformed(ActionEvent actionEvent) {
-            SwingUtilities.invokeLater(new Runnable() {
+            SwingUtilities.invokeLater(() -> {
-                @Override
+                console.setFont(new Font("Monospaced", Font.PLAIN, size));
-                public void run() {
+                mainWindow.pack();
-                    console.setFont(new Font("Monospaced", Font.PLAIN, size));
-                    mainWindow.pack();
-                }
             });
         }
     }
 
     class SetSpeedAction extends AbstractAction {
-        private int speed;
+        private final int speed;
 
         public SetSpeedAction(int speed) {
-            super(Integer.toString(speed) + " MHz", null);
+            super(speed + " MHz", null);
             this.speed = speed;
             putValue(SHORT_DESCRIPTION, "Set simulated speed to " + speed + " MHz.");
         }
@@ -689,7 +715,7 @@ public class Simulator {
     }
 
     class SetCpuAction extends AbstractAction {
-        private Cpu.CpuBehavior behavior;
+        private final Cpu.CpuBehavior behavior;
 
         public SetCpuAction(String cpu, Cpu.CpuBehavior behavior) {
             super(cpu, null);
@@ -729,11 +755,7 @@ public class Simulator {
 
         public void actionPerformed(ActionEvent actionEvent) {
             synchronized (memoryWindow) {
-                if (memoryWindow.isVisible()) {
+                memoryWindow.setVisible(!memoryWindow.isVisible());
-                    memoryWindow.setVisible(false);
-                } else {
-                    memoryWindow.setVisible(true);
-                }
             }
         }
     }
@@ -746,11 +768,7 @@ public class Simulator {
 
         public void actionPerformed(ActionEvent actionEvent) {
             synchronized (videoWindow) {
-                if (videoWindow.isVisible()) {
+                videoWindow.setVisible(!videoWindow.isVisible());
-                    videoWindow.setVisible(false);
-                } else {
-                    videoWindow.setVisible(true);
-                }
             }
         }
     }
@@ -763,11 +781,7 @@ public class Simulator {
 
         public void actionPerformed(ActionEvent actionEvent) {
             synchronized (breakpointsWindow) {
-                if (breakpointsWindow.isVisible()) {
+                breakpointsWindow.setVisible(!breakpointsWindow.isVisible());
-                    breakpointsWindow.setVisible(false);
-                } else {
-                    breakpointsWindow.setVisible(true);
-                }
             }
         }
     }
@@ -963,15 +977,11 @@ public class Simulator {
 
     private void updateVisibleState() {
         // Immediately update the UI.
-        SwingUtilities.invokeLater(new Runnable() {
+        SwingUtilities.invokeLater(() -> {
-            @Override
+            statusPane.updateState();
-            public void run() {
+            memoryWindow.updateState();
-                // Now update the state
+            if (traceLog.shouldUpdate()) {
-                statusPane.updateState();
+                traceLog.refresh();
-                memoryWindow.updateState();
-                if (traceLog.shouldUpdate()) {
-                    traceLog.refresh();
-                }
             }
         });
     }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -32,7 +32,7 @@ import com.loomcom.symon.exceptions.MemoryRangeException;
 
 public abstract class Acia extends Device {
 
-    private String name;
+    private final String name;
 
     /**
      * Register addresses

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -121,9 +121,6 @@ public class Acia6551 extends Acia {
         // Mask the lower four bits to get the baud rate.
         int baudSelector = data & 0x0f;
         switch (baudSelector) {
-            case 0:
-                rate = 0;
-                break;
             case 1:
                 rate = 50;
                 break;
@@ -169,6 +166,8 @@ public class Acia6551 extends Acia {
             case 15:
                 rate = 19200;
                 break;
+            default:
+                break;
         }
 
         setBaudRate(rate);

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

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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
@@ -31,7 +31,7 @@ import com.loomcom.symon.exceptions.MemoryRangeException;
 /**
  * This is a simulation of the Motorola 6850 ACIA, with limited
  * functionality.
- *
+ * <p>
  * Unlike a 16550 UART, the 6850 ACIA has only one-byte transmit and
  * receive buffers. It is the programmer's responsibility to check the
  * status (full or empty) for transmit and receive buffers before

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -26,8 +26,6 @@ package com.loomcom.symon.devices;
 import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
-import java.io.IOException;
-
 /**
  * Simulation of a 6545 CRTC and virtual CRT output.
  */
@@ -87,9 +85,9 @@ public class Crtc extends Device {
     private boolean displayEnableSkew = false;
     private boolean cursorSkew = false;
 
-    private Memory memory;
+    private final Memory memory;
 
-    public Crtc(int deviceAddress, Memory memory) throws MemoryRangeException, IOException {
+    public Crtc(int deviceAddress, Memory memory) throws MemoryRangeException {
         super(deviceAddress, deviceAddress + 2, "CRTC");
         this.memory = memory;
 
@@ -120,19 +118,17 @@ public class Crtc extends Device {
 
     @Override
     public int read(int address, boolean cpuAccess) throws MemoryAccessException {
-        switch (address) {
+        if (address == REGISTER_RW) {
-            case REGISTER_RW:
+            switch (currentRegister) {
-                switch (currentRegister) {
+                case CURSOR_POSITION_LOW:
-                    case CURSOR_POSITION_LOW:
+                    return cursorPosition & 0xff;
-                        return cursorPosition & 0xff;
+                case CURSOR_POSITION_HIGH:
-                    case CURSOR_POSITION_HIGH:
+                    return cursorPosition >> 8;
-                        return cursorPosition >> 8;
+                default:
-                    default:
+                    return 0;
-                        return 0;
+            }
-                }
-            default:
-                return 0;
         }
+        return 0;
     }
 
     @Override

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -45,7 +45,7 @@ public abstract class Device implements Comparable<Device> {
     /**
      * The memory range for this device.
      */
-    private MemoryRange memoryRange;
+    private final MemoryRange memoryRange;
 
     /**
      * The name of the device.
@@ -60,7 +60,7 @@ public abstract class Device implements Comparable<Device> {
     /**
      * Listeners to notify on update.
      */
-    private Set<DeviceChangeListener> deviceChangeListeners;
+    private final Set<DeviceChangeListener> deviceChangeListeners;
 
     public Device(int startAddress, int endAddress, String name) throws MemoryRangeException {
         this.memoryRange = new MemoryRange(startAddress, endAddress);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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/devices/Memory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -30,8 +30,8 @@ import com.loomcom.symon.exceptions.*;
 
 public class Memory extends Device {
 
-    private boolean readOnly;
+    private final boolean readOnly;
-    private int[] mem;
+    private final int[] mem;
 
     /* Initialize all locations to 0x00 (BRK) */
     private static final int DEFAULT_FILL = 0x00;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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/devices/SdController.java

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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
@@ -119,7 +119,10 @@ public class SdController extends Device {
         if (sdImageFile != null) {
             try {
                 FileInputStream fis = new FileInputStream(sdImageFile);
-                fis.skip(this.position);
+                long bytesSkipped = fis.skip(this.position);
+                if (bytesSkipped < this.position) {
+                    logger.log(Level.WARNING, "Failed to seek to position " + 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");

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -27,83 +27,23 @@ import com.loomcom.symon.exceptions.MemoryAccessException;
 import com.loomcom.symon.exceptions.MemoryRangeException;
 
 /**
- * Very basic implementation of a MOS 6522 VIA.
+ * Skeleton for future 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();
+        // TODO: Implement write.
-
-        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, boolean cpuAccess) throws MemoryAccessException {
-        Register[] registers = Register.values();
+        // TODO: Implement read.
-
-        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) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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/jterminal/JTerminal.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
  * Portions Copyright (c) 2009-2011 Graham Edgecombe
  *
  * Permission is hereby granted, free of charge, to any person obtaining
@@ -25,13 +25,8 @@
 package com.loomcom.symon.jterminal;
 
 import com.loomcom.symon.jterminal.vt100.Vt100TerminalModel;
-import java.awt.BorderLayout;
+
-import java.awt.Dimension;
+import java.awt.*;
-import java.awt.Font;
-import java.awt.FontMetrics;
-import java.awt.Graphics;
-import java.awt.event.AdjustmentEvent;
-import java.awt.event.AdjustmentListener;
 import javax.swing.JComponent;
 import javax.swing.JScrollBar;
 
@@ -88,10 +83,6 @@ public class JTerminal extends JComponent {
 		revalidate();
 	}
 
-	public int getBorderWidth() {
-		return borderWidth;
-	}
-
 	public void setFont(Font font) {
 		this.font = font;
 		setCellWidthAndHeight(font);
@@ -113,13 +104,6 @@ public class JTerminal extends JComponent {
 		return model;
 	}
 
-	public void println(String str) {
-		if (str == null) {
-			throw new NullPointerException("str");
-		}
-		print(str.concat("\r\n"));
-	}
-
 	public void print(String str) {
 		model.print(str);
 	}
@@ -177,12 +161,8 @@ public class JTerminal extends JComponent {
 		int bufferSize = model.getBufferSize();
 
 		if (bufferSize > rows) {
-			scrollBar = new JScrollBar(1, 0, rows, 0, bufferSize + 1);
+			scrollBar = new JScrollBar(Adjustable.VERTICAL, 0, rows, 0, bufferSize + 1);
-			scrollBar.addAdjustmentListener(new AdjustmentListener() {
+			scrollBar.addAdjustmentListener(evt -> repaint());
-				public void adjustmentValueChanged(AdjustmentEvent evt) {
-					repaint();
-				}
-			});
 			add("After", scrollBar);
 		}
 

src/main/java/com/loomcom/symon/jterminal/TerminalModel.java

@@ -32,51 +32,45 @@ import com.loomcom.symon.jterminal.bell.BellStrategy;
  */
 public interface TerminalModel {
 
-	/**
-	 * Gets the bell strategy.
-	 * @return The bell strategy.
-	 */
-	public BellStrategy getBellStrategy();
-
 	/**
 	 * Sets the bell strategy.
 	 * @param strategy The bell strategy.
 	 * @throws NullPointerException if the strategy is {@code null}.
 	 */
-	public void setBellStrategy(BellStrategy strategy);
+    void setBellStrategy(BellStrategy strategy);
 
 	/**
 	 * Clears the terminal.
 	 */
-	public void clear();
+    void clear();
 
 	/**
 	 * Moves the cursor back n characters.
 	 * @param n The number of characters.
 	 * @throws IllegalArgumentException if n is not positive.
 	 */
-	public void moveCursorBack(int n);
+    void moveCursorBack(int n);
 
 	/**
 	 * Moves the cursor forward n characters.
 	 * @param n The number of characters.
 	 * @throws IllegalArgumentException if n is not positive.
 	 */
-	public void moveCursorForward(int n);
+    void moveCursorForward(int n);
 
 	/**
 	 * Moves the cursor down n characters.
 	 * @param n The number of characters.
 	 * @throws IllegalArgumentException if n is not positive.
 	 */
-	public void moveCursorDown(int n);
+    void moveCursorDown(int n);
 
 	/**
 	 * Moves the cursor up n characters.
 	 * @param n The number of characters.
 	 * @throws IllegalArgumentException if n is not positive.
 	 */
-	public void moveCursorUp(int n);
+    void moveCursorUp(int n);
 
 	/**
 	 * Sets a cell.
@@ -86,7 +80,7 @@ public interface TerminalModel {
 	 * @throws IndexOutOfBoundsException if the column and/or row number(s) are
 	 * out of bounds.
 	 */
-	public void setCell(int column, int row, TerminalCell cell);
+    void setCell(int column, int row, TerminalCell cell);
 
 	/**
 	 * Gets a cell.
@@ -96,7 +90,7 @@ public interface TerminalModel {
 	 * @throws IndexOutOfBoundsException if the column and/or row number(s) are
 	 * out of bounds.
 	 */
-	public TerminalCell getCell(int column, int row);
+    TerminalCell getCell(int column, int row);
 
 	/**
 	 * Prints the specified string to the terminal at the cursor position,
@@ -105,63 +99,63 @@ public interface TerminalModel {
 	 * @param str The string to print.
 	 * @throws NullPointerException if the string is {@code null}.
 	 */
-	public void print(String str);
+    void print(String str);
 
 	/**
 	 * Gets the number of columns.
 	 * @return The number of columns.
 	 */
-	public int getColumns();
+    int getColumns();
 
 	/**
 	 * Gets the number of rows.
 	 * @return The number of rows.
 	 */
-	public int getRows();
+	int getRows();
 
 	/**
 	 * Gets the buffer size.
 	 * @return The buffer size.
 	 */
-	public int getBufferSize();
+	int getBufferSize();
 
 	/**
 	 * Gets the cursor row.
 	 * @return The cursor row.
 	 */
-	public int getCursorRow();
+	int getCursorRow();
 
 	/**
 	 * Sets the cursor row.
 	 * @param row The cursor row.
 	 * @throws IllegalArgumentException if the row is out of the valid range.
 	 */
-	public void setCursorRow(int row);
+	void setCursorRow(int row);
 
 	/**
 	 * Gets the cursor column.
 	 * @return The cursor column.
 	 */
-	public int getCursorColumn();
+	int getCursorColumn();
 
 	/**
 	 * Sets the cursor column.
 	 * @param column The cursor column.
 	 * @throws IllegalArgumentException if the column is out of the valid range.
 	 */
-	public void setCursorColumn(int column);
+	void setCursorColumn(int column);
 
 	/**
 	 * Gets the default background color.
 	 * @return The default background color.
 	 */
-	public Color getDefaultBackgroundColor();
+	Color getDefaultBackgroundColor();
 
 	/**
 	 * Gets the default foreground color.
 	 * @return The default foreground color.
 	 */
-	public Color getDefaultForegroundColor();
+	Color getDefaultForegroundColor();
 
 }
 

src/main/java/com/loomcom/symon/jterminal/bell/BellStrategy.java

@@ -31,7 +31,7 @@ public interface BellStrategy {
 	/**
 	 * Sounds the bell.
 	 */
-	public void soundBell();
+	void soundBell();
 
 }
 

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

@@ -50,7 +50,7 @@ public class AnsiControlSequence {
 			throw new NullPointerException("parameters");
 		}
 		this.command = command;
-		if (parameters.length == 1 && parameters[0].equals("")) {
+		if (parameters.length == 1 && parameters[0].isEmpty()) {
 			this.parameters = new String[0];
 		} else {
 			this.parameters = parameters.clone();

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

@@ -32,13 +32,13 @@ public interface AnsiControlSequenceListener {
 	 * Called when a control sequence has been parsed.
 	 * @param seq The control sequence.
 	 */
-	public void parsedControlSequence(AnsiControlSequence seq);
+	void parsedControlSequence(AnsiControlSequence seq);
 
 	/**
 	 * Called when a string has been parsed.
 	 * @param str The string.
 	 */
-	public void parsedString(String str);
+	void parsedString(String str);
 
 }
 

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

@@ -33,7 +33,7 @@ import java.io.StringReader;
 public class AnsiControlSequenceParser {
 
 	/**
-	 * The multi-byte control sequence introducer.
+	 * The multibyte control sequence introducer.
 	 */
 	private static final char[] MULTI_CSI = new char[] { 27, '[' };
 
@@ -43,7 +43,7 @@ public class AnsiControlSequenceParser {
 	private static final char SINGLE_CSI = 155;
 
 	/**
-	 * The buffer of data from the last call to {@link #parse()}. This is
+	 * The buffer of data from the last call to "parse()". This is
 	 * populated with data if an escape sequence is not complete.
 	 */
 	private StringBuilder buffer = new StringBuilder();
@@ -70,13 +70,10 @@ public class AnsiControlSequenceParser {
 			str = buffer.toString().concat(str);
 			buffer = new StringBuilder();
 		}
-		Reader reader = new StringReader(str);
+        try {
-		try {
+            try (Reader reader = new StringReader(str)) {
-			try {
+                parse(reader);
-				parse(reader);
+            }
-			} finally {
-				reader.close();
-			}
 		} catch (IOException ex) {
 			/* ignore */
 		}
@@ -147,7 +144,7 @@ public class AnsiControlSequenceParser {
 		if (!finishedSequence) {
 			// not an ideal solution if they used the two byte CSI, but it's
 			// easier and cleaner than keeping track of it
-			buffer.append((char) SINGLE_CSI);
+			buffer.append(SINGLE_CSI);
 			buffer.append(parameters);
 		}
 	}

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

@@ -56,6 +56,7 @@ public class Vt100TerminalModel extends AbstractTerminalModel {
 		@Override
 		public void parsedControlSequence(AnsiControlSequence seq) {
 			char command = seq.getCommand();
+			int n;
 			String[] parameters = seq.getParameters();
 
 			switch (command) {
@@ -63,7 +64,7 @@ public class Vt100TerminalModel extends AbstractTerminalModel {
 			case 'B':
 			case 'C':
 			case 'D':
-				int n = 1;
+				n = 1;
 				if (parameters.length == 1) {
 					n = Integer.parseInt(parameters[0]);
 				}
@@ -73,7 +74,7 @@ public class Vt100TerminalModel extends AbstractTerminalModel {
 					moveCursorDown(n);
 				} else if (command == 'C') {
 					moveCursorForward(n);
-				} else if (command == 'D') {
+				} else {
 					moveCursorBack(n);
 				}
 				break;
@@ -85,7 +86,7 @@ public class Vt100TerminalModel extends AbstractTerminalModel {
 				}
 				if (command == 'E') {
 					moveCursorDown(n);
-				} else if (command == 'F') {
+				} else {
 					moveCursorUp(n);
 				}
 				setCursorColumn(0);
@@ -465,12 +466,7 @@ public class Vt100TerminalModel extends AbstractTerminalModel {
 		return bufferSize;
 	}
 
-	@Override
+    @Override
-	public BellStrategy getBellStrategy() {
-		return bellStrategy;
-	}
-
-	@Override
 	public void setBellStrategy(BellStrategy strategy) {
 		if (strategy == null) {
 			throw new NullPointerException("strategy");

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

@@ -1,7 +1,7 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.com>
+ *                         Maik Merten <maikmerten@googlemail.com>
- *                    Chelsea Wilkinson <mail@chelseawilkinson.me>
+ *                         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

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

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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

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

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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

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

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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
@@ -91,7 +91,7 @@ public class SimpleMachine implements Machine {
     }
 
     @Override
-    public void setRom(Memory rom) throws MemoryRangeException {
+    public void setRom(Memory rom) {
         // No-op
     }
 

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

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -30,10 +30,7 @@ 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;
 
 /**
@@ -46,8 +43,8 @@ public class BreakpointsWindow extends JFrame {
     private static final Dimension FRAME_SIZE = new Dimension(240, 280);
     private static final String EMPTY_STRING = "";
 
-    private JFrame mainWindow;
+    private final JFrame mainWindow;
-    private Breakpoints breakpoints;
+    private final Breakpoints breakpoints;
 
     public BreakpointsWindow(Breakpoints breakpoints,
                              JFrame mainWindow) {
@@ -75,16 +72,7 @@ public class BreakpointsWindow extends JFrame {
         breakpointsTable.setShowGrid(true);
         breakpointsTable.setGridColor(Color.LIGHT_GRAY);
         breakpointsTable.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
-        breakpointsTable.getSelectionModel().addListSelectionListener(new ListSelectionListener() {
+        breakpointsTable.getSelectionModel().addListSelectionListener(e -> removeButton.setEnabled(e.getFirstIndex() > -1));
-            @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);
@@ -92,45 +80,33 @@ public class BreakpointsWindow extends JFrame {
 
         breakpointsPanel.add(scrollPane, BorderLayout.CENTER);
 
-        ActionListener addBreakpointListener = new ActionListener() {
+        ActionListener addBreakpointListener = e -> {
-            @Override
+            int value;
-            public void actionPerformed(ActionEvent e) {
-                int value;
 
-                String newBreakpoint = addTextField.getText();
+            String newBreakpoint = addTextField.getText();
 
-                if (newBreakpoint == null || newBreakpoint.isEmpty()) {
+            if (newBreakpoint == null || newBreakpoint.isEmpty()) {
-                    return;
+                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);
             }
+
+            try {
+                value = (Integer.parseInt(addTextField.getText(), 16) & 0xffff);
+            } catch (NumberFormatException ex) {
+                logger.warn("Can't parse page number {}", newBreakpoint);
+                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() {
+        removeButton.addActionListener(e -> breakpoints.removeBreakpointAtIndex(breakpointsTable.getSelectedRow()));
-            @Override
-            public void actionPerformed(ActionEvent e) {
-                breakpoints.removeBreakpointAtIndex(breakpointsTable.getSelectedRow());
-            }
-        });
 
         controlPanel.add(addTextField);
         controlPanel.add(addButton);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -51,8 +51,8 @@ public class Console extends JTerminal implements KeyListener, MouseListener {
     private static final boolean SWAP_CR_AND_LF       = true;
 
     // If true, send CRLF (0x0d 0x0a) whenever CR is typed
-    private boolean sendCrForLf;
+    private final boolean sendCrForLf;
-    private FifoRingBuffer<Character> typeAheadBuffer;
+    private final FifoRingBuffer<Character> typeAheadBuffer;
 
     public Console(int columns, int rows, Font font, boolean sendCrForLf) {
         super(new Vt100TerminalModel(columns, rows), font);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -49,7 +49,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
 
     private static final Logger logger = LoggerFactory.getLogger(MemoryWindow.class);
 
-    private MemoryTableModel memoryTableModel;
+    private final MemoryTableModel memoryTableModel;
     private JTable memoryTable;
     private JTextField pageNumberTextField;
     private JButton previousPageButton;
@@ -111,7 +111,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
     }
 
     /**
-     * Set-up the UI.
+     * Set up the UI.
      */
     private void createUi() {
         setTitle("Memory Contents");
@@ -230,7 +230,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
      * A JTable that will automatically select all text in a cell
      * being edited.
      */
-    private class MemoryTable extends JTable {
+    private static class MemoryTable extends JTable {
 
         public MemoryTable(TableModel tableModel) {
             super(tableModel);
@@ -242,7 +242,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
 
             final Component editor = getEditorComponent();
 
-            if (editor != null && editor instanceof JTextComponent) {
+            if (editor instanceof JTextComponent) {
                 ((JTextComponent) editor).selectAll();
             }
 
@@ -250,7 +250,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
         }
     }
 
-    private class MemoryTableCellRenderer extends DefaultTableCellRenderer {
+    private static class MemoryTableCellRenderer extends DefaultTableCellRenderer {
 
         @Override
         public Component getTableCellRendererComponent(JTable table, Object value,
@@ -272,9 +272,9 @@ public class MemoryWindow extends JFrame implements ActionListener {
     /**
      * The model that backs the Memory Table.
      */
-    private class MemoryTableModel extends AbstractTableModel {
+    private static class MemoryTableModel extends AbstractTableModel {
 
-        private Bus bus;
+        private final Bus bus;
         private int pageNumber;
 
         private static final int COLUMN_COUNT = 17;

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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/ui/StatusPanel.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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/ui/TraceLog.java

@@ -1,6 +1,6 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 Seth J. Morabito <web@loomcom.com>
- *                    Maik Merten <maikmerten@googlemail.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

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -64,12 +64,13 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
     private static final long WINDOW_REPAINT_INTERVAL = 66; // 30fps rate
     private static final int CHAR_WIDTH = 8;
     private static final int CHAR_HEIGHT = 8;
+    private static final String ASCII_ROM = "/ascii.rom";
 
     private final int scaleX, scaleY;
     private final boolean shouldScale;
 
     private BufferedImage image;
-    private int[] charRom;
+    private final int[] charRom;
 
     private int horizontalDisplayed;
     private int verticalDisplayed;
@@ -78,9 +79,9 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
     private boolean hideCursor;
 
     private Dimension dimensions;
-    private Crtc crtc;
+    private final Crtc crtc;
 
-    private ScheduledExecutorService scheduler;
+    private final ScheduledExecutorService scheduler;
     private ScheduledFuture<?> cursorBlinker;
 
     /**
@@ -123,12 +124,9 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
      */
     private class CursorBlinker implements Runnable {
         public void run() {
-            SwingUtilities.invokeLater(new Runnable() {
+            SwingUtilities.invokeLater(() -> {
-                @Override
+                if (cursorBlinkRate > 0) {
-                public void run() {
+                    hideCursor = !hideCursor;
-                    if (cursorBlinkRate > 0) {
-                        hideCursor = !hideCursor;
-                    }
                 }
             });
         }
@@ -136,12 +134,9 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
     private class WindowPainter implements Runnable {
         public void run() {
-            SwingUtilities.invokeLater(new Runnable () {
+            SwingUtilities.invokeLater(() -> {
-                @Override
+                if (VideoWindow.this.isVisible()) {
-                public void run() {
+                    VideoWindow.this.repaint();
-                    if (VideoWindow.this.isVisible()) {
-                        VideoWindow.this.repaint();
-                    }
                 }
             });
         }
@@ -152,7 +147,7 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
 
         this.scheduler = Executors.newSingleThreadScheduledExecutor();
         this.crtc = crtc;
-        this.charRom = loadCharRom("/ascii.rom");
+        this.charRom = loadCharRom();
         this.scaleX = scaleX;
         this.scaleY = scaleY;
         this.shouldScale = (scaleX > 1 || scaleY > 1);
@@ -292,14 +287,17 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
      * Since the BufferedImage is a TYPE_BYTE_BINARY, the data must be converted
      * into a single byte per pixel, 0 for black and 255 for white.
 
-     * @param resource The ROM file resource to load.
      * @return An array of glyphs, each ready for insertion.
-     * @throws IOException
+     * @throws IOException Failure to load character ROM.
      */
-    private int[] loadCharRom(String resource) throws IOException {
+    private int[] loadCharRom() throws IOException {
-        BufferedInputStream bis = null;
+        var resource = this.getClass().getResourceAsStream(ASCII_ROM);
-        try {
+
-            bis = new BufferedInputStream(this.getClass().getResourceAsStream(resource));
+        if (resource == null) {
+            throw new IOException("Resource " + ASCII_ROM + " not found");
+        }
+
+        try (BufferedInputStream bis = new BufferedInputStream(resource)) {
             ByteArrayOutputStream bos = new ByteArrayOutputStream();
             while (bis.available() > 0) {
                 bos.write(bis.read());
@@ -314,7 +312,7 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
             int[] converted = new int[raw.length * CHAR_WIDTH];
 
             int romIndex = 0;
-            for (int i = 0; i < converted.length;) {
+            for (int i = 0; i < converted.length; ) {
                 byte charRow = raw[romIndex++];
 
                 for (int j = 7; j >= 0; j--) {
@@ -322,10 +320,6 @@ public class VideoWindow extends JFrame implements DeviceChangeListener {
                 }
             }
             return converted;
-        } finally {
-            if (bis != null) {
-                bis.close();
-            }
         }
     }
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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
@@ -34,8 +34,8 @@ import java.util.Queue;
  */
 public class FifoRingBuffer<E> implements Iterable<E> {
 
-    private Queue<E> fifoBuffer;
+    private final Queue<E> fifoBuffer;
-    private int maxLength;
+    private final int maxLength;
 
     public FifoRingBuffer(int maxLength) {
         this.fifoBuffer = new LinkedList<>();

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2016 Seth J. Morabito <web@loomcom.com>
+ * Copyright (c) 2008-2025 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/test/java/com/loomcom/symon/CpuTest.java

@@ -670,4 +670,78 @@ public class CpuTest extends TestCase {
         cpu.step();
         assertEquals(0x3E, cpu.getAccumulator());
     }
+
+    // Have tests:
+    //    ACC, AIX, ABS, ABX, ABY, IMP, IMM, IND, XIN, INY,
+    //    REL, ZPG, ZPI
+
+    // Need to test:
+    //    ZPR, ZPX, ZPY, NUL
+
+    // Question: Should 'NUL' even exist? Isn't it just 'IMP'?
+
+    public void testDisassembleOpHandlesAccumulatorCorrectly() {
+        var dis = Cpu.disassembleOp(0x2a, new int[]{});
+        assertEquals("ROL", dis);
+    }
+
+    public void testDisassembleOpHandlesAbsoluteXIndexedIndirectCorrectly() {
+        var dis = Cpu.disassembleOp(0x7c, new int[]{0x00, 0x1a});
+        assertEquals("JMP ($1A00,X)", dis);
+    }
+
+    public void testDisassembleOpHandlesAbsoluteCorrectly() {
+        var dis = Cpu.disassembleOp(0x0d, new int[]{0x10, 0x0c});
+        assertEquals("ORA $0C10", dis);
+    }
+
+    public void testDisassembleOpHandlesAbsoluteXIndexedCorrectly() {
+        var dis = Cpu.disassembleOp(0x1d, new int[]{0x00, 0x1c});
+        assertEquals("ORA $1C00,X", dis);
+    }
+
+    public void testDisassembleOpHandlesAbsoluteYIndexedCorrectly() {
+        var dis = Cpu.disassembleOp(0x19, new int[]{0x00, 0x1c});
+        assertEquals("ORA $1C00,Y", dis);
+    }
+
+    public void testDisassembleOpHandlesImpliedCorrectly() {
+        var dis = Cpu.disassembleOp(0x00, new int[]{});
+        assertEquals("BRK", dis);
+    }
+
+    public void testDisassembleOpHandlesIndirectCorrectly() {
+        var dis = Cpu.disassembleOp(0x6c, new int[]{0x00, 0x1c});
+        assertEquals("JMP ($1C00)", dis);
+    }
+
+    public void testDisassembleOpHandlesImmediateCorrectly() {
+        var dis = Cpu.disassembleOp(0xA9, new int[]{0xff});
+        assertEquals("LDA #$FF", dis);
+    }
+
+    public void testDisassembleOpHandlesXIndexedIndirectCorrectly() {
+        var dis = Cpu.disassembleOp(0x01, new int[]{0x10});
+        assertEquals("ORA ($10,X)", dis);
+    }
+
+    public void testDisassembleOpHandlesIndirectYIndexedCorrectly() {
+        var dis = Cpu.disassembleOp(0x11, new int[]{0x10});
+        assertEquals("ORA ($10),Y", dis);
+    }
+
+    public void testDisassembleOpHandlesRelativeCorrectly() {
+        var dis = Cpu.disassembleOp(0x10, new int[]{0xff});
+        assertEquals("BPL $FF", dis);
+    }
+
+    public void testDisassembleOpHandlesZeroPageCorrectly() {
+        var dis = Cpu.disassembleOp(0x24, new int[]{0x10});
+        assertEquals("BIT $10", dis);
+    }
+
+    public void testDisassembleOpHandlesZeroPageIndirectCorrectly() throws Exception {
+        var dis = Cpu.disassembleOp(0xB2, new int[]{0x1a});
+        assertEquals("LDA ($1A)", dis);
+    }
 }