Release 1.2.0

README.md

@@ -1,9 +1,9 @@
 SYMON - A 6502 System Simulator
 ===============================
 
-**Version:** 1.1.1
+**Version:** 1.2.0
 
-**Last Updated:** 2 January, 2016
+**Last Updated:** 3 January, 2016
 
 See the file COPYING for license.
 
@@ -188,7 +188,7 @@ Maven will build Symon, run unit tests, and produce a jar file in the
 Symon is meant to be invoked directly from the jar file. To run with
 Java 1.8 or greater, just type:
 
-    $ java -jar symon-1.1.1.jar
+    $ java -jar symon-1.2.0.jar
 
 When Symon is running, you should be presented with a simple graphical
 interface.
@@ -235,6 +235,9 @@ running.
 
 ## 5.0 Revision History
 
+  - **1.2.0:** 3 January, 2016 - Add symbolic disassembly to breakpoints
+    window.
+  
   - **1.1.1:** 2 January, 2016 - Minor enhancement: Allows breakpoints
     to be added with the Enter key.
 
@@ -286,7 +289,15 @@ running.
 
   - **0.1:** 20 January, 2010
 
-## 6.0 To Do
+## 6.0 Roadmap
+
+  - **1.2:** Better breakpoint support. Symbolic debugging of breakpoints.
+
+  - **2.0:** Complete rewrite of the UI in JavaFX instead of Swing. Complete
+    assembler and disassembler built in. Ability to attach source code for
+    symbolic debugging.
+
+## 7.0 To Do
 
   - Feedback (in the form of dialogs, status bar, etc).
 
@@ -310,7 +321,7 @@ running.
 
   - Symbolic debugging.
 
-## 7.0 Copyright and Acknowledgements
+## 8.0 Copyright and Acknowledgements
 
 **Copyright (c) 2014 Seth J. Morabito <web@loomcom.com>**
 
@@ -330,7 +341,7 @@ This project would not have been possible without the following resources:
   - [Neil Parker's "The 6502/65C02/65C816 Instruction Set Decoded"] (http://www.llx.com/~nparker/a2/opcodes.html),
     for information about how instructions are coded
 
-## 8.0 Licensing
+## 9.0 Licensing
 
 Symon is free software.  It is distributed under the MIT License.
 Please see the file 'COPYING' for full details of the license.

pom.xml

@@ -4,7 +4,7 @@
     <groupId>com.loomcom.symon</groupId>
     <artifactId>symon</artifactId>
     <packaging>jar</packaging>
-    <version>1.1.1</version>
+    <version>1.2.0</version>
     <name>symon</name>
     <url>http://www.loomcom.com/symon</url>
     <properties>

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

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

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

@@ -24,7 +24,7 @@
 package com.loomcom.symon;
 
 import com.loomcom.symon.exceptions.MemoryAccessException;
-import com.loomcom.symon.util.HexUtil;
+import com.loomcom.symon.util.Utils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -70,7 +70,7 @@ public class Cpu implements InstructionTable {
     private Bus bus;
 
     /* The CPU state */
-    private static final CpuState state = new CpuState();
+    private final CpuState state = new CpuState();
 
     /* start time of op execution, needed for speed simulation */
     private long opBeginTime;
@@ -114,7 +114,7 @@ public class Cpu implements InstructionTable {
         state.sp = 0xff;
 
         // Set the PC to the address stored in the reset vector
-        state.pc = address(bus.read(RST_VECTOR_L), bus.read(RST_VECTOR_H));
+        state.pc = Utils.address(bus.read(RST_VECTOR_L), bus.read(RST_VECTOR_H));
 
         // Clear instruction register.
         state.ir = 0;
@@ -202,7 +202,7 @@ public class Cpu implements InstructionTable {
                     case 2: // Accumulator - ignored
                         break;
                     case 3: // Absolute
-                        effectiveAddress = address(state.args[0], state.args[1]);
+                        effectiveAddress = Utils.address(state.args[0], state.args[1]);
                         break;
                     case 5: // Zero Page,X / Zero Page,Y
                         if (state.ir == 0x96 || state.ir == 0xb6) {
@@ -224,7 +224,7 @@ public class Cpu implements InstructionTable {
                 switch (irAddressMode) {
                     case 0: // (Zero Page,X)
                         tmp = (state.args[0] + state.x) & 0xff;
-                        effectiveAddress = address(bus.read(tmp), bus.read(tmp + 1));
+                        effectiveAddress = Utils.address(bus.read(tmp), bus.read(tmp + 1));
                         break;
                     case 1: // Zero Page
                         effectiveAddress = state.args[0];
@@ -233,10 +233,10 @@ public class Cpu implements InstructionTable {
                         effectiveAddress = -1;
                         break;
                     case 3: // Absolute
-                        effectiveAddress = address(state.args[0], state.args[1]);
+                        effectiveAddress = Utils.address(state.args[0], state.args[1]);
                         break;
                     case 4: // (Zero Page),Y
-                        tmp = address(bus.read(state.args[0]),
+                        tmp = Utils.address(bus.read(state.args[0]),
                                       bus.read((state.args[0] + 1) & 0xff));
                         effectiveAddress = (tmp + state.y) & 0xffff;
                         break;
@@ -277,7 +277,7 @@ public class Cpu implements InstructionTable {
             case 0x20: // JSR - Jump to Subroutine - Implied
                 stackPush((state.pc - 1 >> 8) & 0xff); // PC high byte
                 stackPush(state.pc - 1 & 0xff);        // PC low byte
-                state.pc = address(state.args[0], state.args[1]);
+                state.pc = Utils.address(state.args[0], state.args[1]);
                 break;
             case 0x28: // PLP - Pull Processor Status - Implied
                 setProcessorStatus(stackPop());
@@ -294,7 +294,7 @@ public class Cpu implements InstructionTable {
                 setProcessorStatus(stackPop());
                 int lo = stackPop();
                 int hi = stackPop();
-                setProgramCounter(address(lo, hi));
+                setProgramCounter(Utils.address(lo, hi));
                 break;
             case 0x48: // PHA - Push Accumulator - Implied
                 stackPush(state.a);
@@ -310,7 +310,7 @@ public class Cpu implements InstructionTable {
             case 0x60: // RTS - Return from Subroutine - Implied
                 lo = stackPop();
                 hi = stackPop();
-                setProgramCounter((address(lo, hi) + 1) & 0xffff);
+                setProgramCounter((Utils.address(lo, hi) + 1) & 0xffff);
                 break;
             case 0x68: // PLA - Pull Accumulator - Implied
                 state.a = stackPop();
@@ -398,20 +398,20 @@ public class Cpu implements InstructionTable {
 
             /** JMP *****************************************************************/
             case 0x4c: // JMP - Absolute
-                state.pc = address(state.args[0], state.args[1]);
+                state.pc = Utils.address(state.args[0], state.args[1]);
                 break;
             case 0x6c: // JMP - Indirect
-                lo = address(state.args[0], state.args[1]); // Address of low byte
+                lo = Utils.address(state.args[0], state.args[1]); // Address of low byte
 
                 if (state.args[0] == 0xff &&
                     (behavior == CpuBehavior.NMOS_WITH_INDIRECT_JMP_BUG ||
                      behavior == CpuBehavior.NMOS_WITH_ROR_BUG)) {
-                    hi = address(0x00, state.args[1]);
+                    hi = Utils.address(0x00, state.args[1]);
                 } else {
                     hi = lo + 1;
                 }
 
-                state.pc = address(bus.read(lo), bus.read(hi));
+                state.pc = Utils.address(bus.read(lo), bus.read(hi));
                 /* TODO: For accuracy, allow a flag to enable broken behavior of early 6502s:
                  *
                  * "An original 6502 has does not correctly fetch the target
@@ -770,7 +770,7 @@ public class Cpu implements InstructionTable {
         setIrqDisableFlag();
 
         // Load interrupt vector address into PC
-        state.pc = address(bus.read(vectorLow), bus.read(vectorHigh));
+        state.pc = Utils.address(bus.read(vectorLow), bus.read(vectorHigh));
     }
 
     /**
@@ -1198,23 +1198,23 @@ public class Cpu implements InstructionTable {
     }
 
     public String getAccumulatorStatus() {
-        return "$" + HexUtil.byteToHex(state.a);
+        return "$" + Utils.byteToHex(state.a);
     }
 
     public String getXRegisterStatus() {
-        return "$" + HexUtil.byteToHex(state.x);
+        return "$" + Utils.byteToHex(state.x);
     }
 
     public String getYRegisterStatus() {
-        return "$" + HexUtil.byteToHex(state.y);
+        return "$" + Utils.byteToHex(state.y);
     }
 
     public String getProgramCounterStatus() {
-        return "$" + HexUtil.wordToHex(state.pc);
+        return "$" + Utils.wordToHex(state.pc);
     }
 
     public String getStackPointerStatus() {
-        return "$" + HexUtil.byteToHex(state.sp);
+        return "$" + Utils.byteToHex(state.sp);
     }
 
     public int getProcessorStatus() {
@@ -1298,19 +1298,12 @@ public class Cpu implements InstructionTable {
         }
     }
 
-    /**
-     * Given two bytes, return an address.
-     */
-    int address(int lowByte, int hiByte) {
-        return ((hiByte << 8) | lowByte) & 0xffff;
-    }
-
     /**
      * Given a hi byte and a low byte, return the Absolute,X
      * offset address.
      */
     int xAddress(int lowByte, int hiByte) {
-        return (address(lowByte, hiByte) + state.x) & 0xffff;
+        return (Utils.address(lowByte, hiByte) + state.x) & 0xffff;
     }
 
     /**
@@ -1318,7 +1311,7 @@ public class Cpu implements InstructionTable {
      * offset address.
      */
     int yAddress(int lowByte, int hiByte) {
-        return (address(lowByte, hiByte) + state.y) & 0xffff;
+        return (Utils.address(lowByte, hiByte) + state.y) & 0xffff;
     }
 
     /**
@@ -1362,249 +1355,81 @@ public class Cpu implements InstructionTable {
         } while (opBeginTime + interval >= end);
     }
 
+    /**
+     * Return a formatted string representing the last instruction and
+     * operands that were executed.
+     *
+     * @return A string representing the mnemonic and operands of the instruction
+     */
+    public static String disassembleOp(int opCode, int[] args) {
+        String mnemonic = opcodeNames[opCode];
+
+        if (mnemonic == null) {
+            return "???";
+        }
+
+        StringBuilder sb = new StringBuilder(mnemonic);
+
+        switch (instructionModes[opCode]) {
+            case ABS:
+                sb.append(" $").append(Utils.wordToHex(Utils.address(args[0], args[1])));
+                break;
+            case ABX:
+                sb.append(" $").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(",X");
+                break;
+            case ABY:
+                sb.append(" $").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(",Y");
+                break;
+            case IMM:
+                sb.append(" #$").append(Utils.byteToHex(args[0]));
+                break;
+            case IND:
+                sb.append(" ($").append(Utils.wordToHex(Utils.address(args[0], args[1]))).append(")");
+                break;
+            case XIN:
+                sb.append(" ($").append(Utils.byteToHex(args[0])).append(",X)");
+                break;
+            case INY:
+                sb.append(" ($").append(Utils.byteToHex(args[0])).append("),Y");
+                break;
+            case REL:
+            case ZPG:
+                sb.append(" $").append(Utils.byteToHex(args[0]));
+                break;
+            case ZPX:
+                sb.append(" $").append(Utils.byteToHex(args[0])).append(",X");
+                break;
+            case ZPY:
+                sb.append(" $").append(Utils.byteToHex(args[0])).append(",Y");
+                break;
+        }
+
+        return sb.toString();
+    }
 
     /**
-     * A compact, struct-like representation of CPU state.
+     * Return a formatted string representing the next instruction and
+     * operands to be executed.
+     *
+     * @return A string representing the mnemonic and operands of the instruction
      */
-    public static class CpuState {
+    public String disassembleNextOp() {
-        /**
+        return Cpu.disassembleOp(state.nextIr, state.nextArgs);
-         * Accumulator
+    }
-         */
-        public int a;
-        /**
-         * X index regsiter
-         */
-        public int x;
-        /**
-         * Y index register
-         */
-        public int y;
-        /**
-         * Stack Pointer
-         */
-        public int sp;
-        /**
-         * Program Counter
-         */
-        public int pc;
-        /**
-         * Last Loaded Instruction Register
-         */
-        public int ir;
-        /**
-         * Peek-Ahead to next IR
-         */
-        public int nextIr;
-        public int[] args = new int[2];
-        public int[] nextArgs = new int[2];
-        public int instSize;
-        public boolean opTrap;
-        public boolean irqAsserted;
-        public boolean nmiAsserted;
-        public int lastPc;
 
-        /* Status Flag Register bits */
+    /**
-        public boolean carryFlag;
+     * @param address Address to disassemble
-        public boolean negativeFlag;
+     * @return String containing the disassembled instruction and operands.
-        public boolean zeroFlag;
+     */
-        public boolean irqDisableFlag;
+    public String disassembleOpAtAddress(int address) throws MemoryAccessException {
-        public boolean decimalModeFlag;
+        int opCode = bus.read(address);
-        public boolean breakFlag;
+        int args[] = new int[2];
-        public boolean overflowFlag;
+        int size = Cpu.instructionSizes[opCode];
-        public long stepCounter = 0L;
+        for (int i = 1; i < size; i++) {
-
+            int nextRead = (address + i) % bus.endAddress();
-        /**
+            args[i-1] = bus.read(nextRead);
-         * Create an empty CPU State.
-         */
-        public CpuState() {}
-
-        /**
-         * Snapshot a copy of the CpuState.
-         *
-         * (This is a copy constructor rather than an implementation of <code>Cloneable</code>
-         * based on Josh Bloch's recommendation)
-         *
-         * @param s The CpuState to copy.
-         */
-        public CpuState(CpuState s) {
-            this.a = s.a;
-            this.x = s.x;
-            this.y = s.y;
-            this.sp = s.sp;
-            this.pc = s.pc;
-            this.ir = s.ir;
-            this.nextIr = s.nextIr;
-            this.lastPc = s.lastPc;
-            this.args[0] = s.args[0];
-            this.args[1] = s.args[1];
-            this.nextArgs[0] = s.nextArgs[0];
-            this.nextArgs[1] = s.nextArgs[1];
-            this.instSize = s.instSize;
-            this.opTrap = s.opTrap;
-            this.irqAsserted = s.irqAsserted;
-            this.carryFlag = s.carryFlag;
-            this.negativeFlag = s.negativeFlag;
-            this.zeroFlag = s.zeroFlag;
-            this.irqDisableFlag = s.irqDisableFlag;
-            this.decimalModeFlag = s.decimalModeFlag;
-            this.breakFlag = s.breakFlag;
-            this.overflowFlag = s.overflowFlag;
-            this.stepCounter = s.stepCounter;
         }
 
-        /**
+        return disassembleOp(opCode, args);
-         * Returns a string formatted for the trace log.
-         *
-         * @return a string formatted for the trace log.
-         */
-        public String toTraceEvent() {
-            String opcode = disassembleLastOp();
-            return getInstructionByteStatus() + "  " +
-                    String.format("%-14s", opcode) +
-                    "A:" + HexUtil.byteToHex(a) + " " +
-                    "X:" + HexUtil.byteToHex(x) + " " +
-                    "Y:" + HexUtil.byteToHex(y) + " " +
-                    "F:" + HexUtil.byteToHex(getStatusFlag()) + " " +
-                    "S:1" + HexUtil.byteToHex(sp) + " " +
-                    getProcessorStatusString() + "\n";
-        }
-
-        /**
-         * @return The value of the Process Status Register, as a byte.
-         */
-        public int getStatusFlag() {
-            int status = 0x20;
-            if (carryFlag) {
-                status |= P_CARRY;
-            }
-            if (zeroFlag) {
-                status |= P_ZERO;
-            }
-            if (irqDisableFlag) {
-                status |= P_IRQ_DISABLE;
-            }
-            if (decimalModeFlag) {
-                status |= P_DECIMAL;
-            }
-            if (breakFlag) {
-                status |= P_BREAK;
-            }
-            if (overflowFlag) {
-                status |= P_OVERFLOW;
-            }
-            if (negativeFlag) {
-                status |= P_NEGATIVE;
-            }
-            return status;
-        }
-
-        public String getInstructionByteStatus() {
-            switch (Cpu.instructionSizes[ir]) {
-                case 0:
-                case 1:
-                    return HexUtil.wordToHex(lastPc) + "  " +
-                           HexUtil.byteToHex(ir) + "      ";
-                case 2:
-                    return HexUtil.wordToHex(lastPc) + "  " +
-                           HexUtil.byteToHex(ir) + " " +
-                           HexUtil.byteToHex(args[0]) + "   ";
-                case 3:
-                    return HexUtil.wordToHex(lastPc) + "  " +
-                           HexUtil.byteToHex(ir) + " " +
-                           HexUtil.byteToHex(args[0]) + " " +
-                           HexUtil.byteToHex(args[1]);
-                default:
-                    return null;
-            }
-        }
-
-        /**
-         * Return a formatted string representing the last instruction and
-         * operands that were executed.
-         *
-         * @return A string representing the mnemonic and operands of the instruction
-         */
-        private String disassembleOp(int ir, int[] args) {
-            String mnemonic = opcodeNames[ir];
-
-            if (mnemonic == null) {
-                return "???";
-            }
-
-            StringBuilder sb = new StringBuilder(mnemonic);
-
-            switch (instructionModes[ir]) {
-                case ABS:
-                    sb.append(" $").append(HexUtil.wordToHex(address(args[0], args[1])));
-                    break;
-                case ABX:
-                    sb.append(" $").append(HexUtil.wordToHex(address(args[0], args[1]))).append(",X");
-                    break;
-                case ABY:
-                    sb.append(" $").append(HexUtil.wordToHex(address(args[0], args[1]))).append(",Y");
-                    break;
-                case IMM:
-                    sb.append(" #$").append(HexUtil.byteToHex(args[0]));
-                    break;
-                case IND:
-                    sb.append(" ($").append(HexUtil.wordToHex(address(args[0], args[1]))).append(")");
-                    break;
-                case XIN:
-                    sb.append(" ($").append(HexUtil.byteToHex(args[0])).append(",X)");
-                    break;
-                case INY:
-                    sb.append(" ($").append(HexUtil.byteToHex(args[0])).append("),Y");
-                    break;
-                case REL:
-                case ZPG:
-                    sb.append(" $").append(HexUtil.byteToHex(args[0]));
-                    break;
-                case ZPX:
-                    sb.append(" $").append(HexUtil.byteToHex(args[0])).append(",X");
-                    break;
-                case ZPY:
-                    sb.append(" $").append(HexUtil.byteToHex(args[0])).append(",Y");
-                    break;
-            }
-
-            return sb.toString();
-        }
-
-        public String disassembleLastOp() {
-            return disassembleOp(ir, args);
-        }
-
-        /**
-         * Return a formatted string representing the next instruction and
-         * operands to be executed.
-         *
-         * @return A string representing the mnemonic and operands of the instruction
-         */
-        public String disassembleNextOp() {
-            return disassembleOp(nextIr, nextArgs);
-        }
-
-        /**
-         * Given two bytes, return an address.
-         */
-        private int address(int lowByte, int hiByte) {
-            return ((hiByte << 8) | lowByte) & 0xffff;
-        }
-
-
-        /**
-         * @return A string representing the current status register state.
-         */
-        public String getProcessorStatusString() {
-            return "[" + (negativeFlag ? 'N' : '.') +
-                    (overflowFlag ? 'V' : '.') +
-                    "-" +
-                    (breakFlag ? 'B' : '.') +
-                    (decimalModeFlag ? 'D' : '.') +
-                    (irqDisableFlag ? 'I' : '.') +
-                    (zeroFlag ? 'Z' : '.') +
-                    (carryFlag ? 'C' : '.') +
-                    "]";
-        }
     }
 }

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

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

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

@@ -119,7 +119,7 @@ public class Simulator {
     private JFileChooser fileChooser;
     private PreferencesDialog preferences;
 
-    private SortedSet<Integer> breakpoints;
+    private Breakpoints breakpoints;
 
     private final Object commandMonitorObject = new Object();
 
@@ -136,7 +136,7 @@ public class Simulator {
     private static final String[] STEPS = {"1", "5", "10", "20", "50", "100"};
 
     public Simulator(Class machineClass) throws Exception {
-        this.breakpoints = new TreeSet<>();
+        this.breakpoints = new Breakpoints(this);
 
         this.machine = (Machine) machineClass.getConstructors()[0].newInstance();
 
@@ -443,6 +443,10 @@ public class Simulator {
         }
     }
 
+    public String disassembleOpAtAddress(int address) throws MemoryAccessException {
+        return machine.getCpu().disassembleOpAtAddress(address);
+    }
+
     class LoadProgramAction extends AbstractAction {
         public LoadProgramAction() {
             super("Load Program...", null);
@@ -473,10 +477,14 @@ public class Simulator {
                                 program[i++] = dis.readByte();
                             }
 
-                            SwingUtilities.invokeLater(() -> console.reset());
-
                             // Now load the program at the starting address.
                             loadProgram(program, preferences.getProgramStartAddress());
+
+                            SwingUtilities.invokeLater(() -> {
+                                console.reset();
+                                breakpoints.refresh();
+                            });
+
                             // TODO: "Don't Show Again" checkbox
                             JOptionPane.showMessageDialog(mainWindow,
                                     "Loaded Successfully At " +
@@ -524,6 +532,9 @@ public class Simulator {
 
                         updateVisibleState();
 
+                        // Refresh breakpoints to show new memory contents.
+                        breakpoints.refresh();
+
                         logger.info("ROM File `{}' loaded at {}", romFile.getName(),
                                 String.format("0x%04X", machine.getRomBase()));
                         // TODO: "Don't Show Again" checkbox

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

@@ -23,7 +23,8 @@
 
 package com.loomcom.symon.ui;
 
-import com.loomcom.symon.util.HexUtil;
+import com.loomcom.symon.Breakpoints;
+import com.loomcom.symon.util.Utils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -31,8 +32,6 @@ import javax.swing.*;
 import javax.swing.border.EmptyBorder;
 import java.awt.*;
 import java.awt.event.ActionListener;
-import java.util.ArrayList;
-import java.util.SortedSet;
 
 /**
  * Simple window to enter breakpoints.
@@ -45,45 +44,9 @@ public class BreakpointsWindow extends JFrame {
     private static final String EMPTY_STRING = "";
 
     private JFrame mainWindow;
-    private SortedSet<Integer> breakpoints;
+    private Breakpoints breakpoints;
 
-    /**
+    public BreakpointsWindow(Breakpoints breakpoints,
-     * Simple ListModel to back the list of breakpoints.
-     */
-    private class BreakpointsListModel extends AbstractListModel<String> {
-        private SortedSet<Integer> breakpoints;
-
-        public BreakpointsListModel(SortedSet<Integer> breakpoints) {
-            this.breakpoints = breakpoints;
-        }
-
-        @Override
-        public int getSize() {
-            return breakpoints.size();
-        }
-
-        @Override
-        public String getElementAt(int index) {
-            ArrayList<Integer> values = new ArrayList<>(breakpoints);
-            return "$" + HexUtil.wordToHex(values.get(index));
-        }
-
-        public void addElement(Integer breakpoint) {
-            breakpoints.add(breakpoint);
-            ArrayList<Integer> values = new ArrayList<>(breakpoints);
-            int index = values.indexOf(breakpoint);
-            fireIntervalAdded(this, index, index);
-        }
-
-        public void removeElement(int index) {
-            ArrayList<Integer> values = new ArrayList<>(breakpoints);
-            Integer breakpoint = values.get(index);
-            breakpoints.remove(breakpoint);
-            fireIntervalRemoved(this, index, index);
-        }
-    }
-
-    public BreakpointsWindow(SortedSet<Integer> breakpoints,
                              JFrame mainWindow) {
         this.breakpoints = breakpoints;
         this.mainWindow = mainWindow;
@@ -103,30 +66,26 @@ public class BreakpointsWindow extends JFrame {
         JButton removeButton = new JButton("Del");
         removeButton.setEnabled(false);
 
-        JTextField addTextField = new JTextField(5);
+        JTextField addTextField = new JTextField(4);
 
-        BreakpointsListModel listModel = new BreakpointsListModel(breakpoints);
+        JTable breakpointsTable = new JTable(breakpoints);
-        JList<String> breakpointsList = new JList<>(listModel);
+        breakpointsTable.setShowGrid(true);
-        breakpointsList.setFont(new Font("Monospace", Font.PLAIN, 14));
+        breakpointsTable.setGridColor(Color.LIGHT_GRAY);
-        breakpointsList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
+        breakpointsTable.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
+        breakpointsTable.getSelectionModel().addListSelectionListener(e -> {
+            if (e.getFirstIndex() > -1) {
+                removeButton.setEnabled(true);
+            } else {
+                removeButton.setEnabled(false);
+            }
+        });
 
-        JScrollPane scrollPane = new JScrollPane(breakpointsList);
+        JScrollPane scrollPane = new JScrollPane(breakpointsTable);
         scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
         scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
 
         breakpointsPanel.add(scrollPane, BorderLayout.CENTER);
 
-
-        breakpointsList.addListSelectionListener(le -> {
-            int idx = breakpointsList.getSelectedIndex();
-
-            if (idx == -1) {
-                removeButton.setEnabled(false);
-            } else {
-                removeButton.setEnabled(true);
-            }
-        });
-
         ActionListener addBreakpointListener = e -> {
             int value = -1;
 
@@ -147,9 +106,9 @@ public class BreakpointsWindow extends JFrame {
                 return;
             }
 
-            listModel.addElement(value);
+            breakpoints.addBreakpoint(value);
 
-            logger.debug("Added breakpoint ${}", HexUtil.wordToHex(value));
+            logger.debug("Added breakpoint ${}", Utils.wordToHex(value));
 
             addTextField.setText(EMPTY_STRING);
         };
@@ -157,7 +116,7 @@ public class BreakpointsWindow extends JFrame {
         addButton.addActionListener(addBreakpointListener);
         addTextField.addActionListener(addBreakpointListener);
 
-        removeButton.addActionListener(e -> listModel.removeElement(breakpointsList.getSelectedIndex()));
+        removeButton.addActionListener(e -> breakpoints.removeBreakpointAtIndex(breakpointsTable.getSelectedRow()));
 
         controlPanel.add(addTextField);
         controlPanel.add(addButton);

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

@@ -25,7 +25,7 @@ package com.loomcom.symon.ui;
 
 import com.loomcom.symon.Bus;
 import com.loomcom.symon.exceptions.MemoryAccessException;
-import com.loomcom.symon.util.HexUtil;
+import com.loomcom.symon.util.Utils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -107,7 +107,7 @@ public class MemoryWindow extends JFrame implements ActionListener {
 
         previousPageButton.setEnabled(pageNumber > 0x00);
         nextPageButton.setEnabled(pageNumber < 0xff);
-        pageNumberTextField.setText(HexUtil.byteToHex(pageNumber));
+        pageNumberTextField.setText(Utils.byteToHex(pageNumber));
     }
 
     /**
@@ -328,13 +328,13 @@ public class MemoryWindow extends JFrame implements ActionListener {
         public Object getValueAt(int row, int column) {
             try {
                 if (column == 0) {
-                    return HexUtil.wordToHex(fullAddress(row, 1));
+                    return Utils.wordToHex(fullAddress(row, 1));
                 } else if (column < 9) {
                     // Display hex value of the data
-                    return HexUtil.byteToHex(bus.read(fullAddress(row, column)));
+                    return Utils.byteToHex(bus.read(fullAddress(row, column)));
                 } else {
                     // Display the ASCII equivalent (if printable)
-                    return HexUtil.byteToAscii(bus.read(fullAddress(row, column - 8)));
+                    return Utils.byteToAscii(bus.read(fullAddress(row, column - 8)));
                 }
             } catch (MemoryAccessException ex) {
                 return "??";

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

@@ -24,14 +24,13 @@
 package com.loomcom.symon.ui;
 
 import com.loomcom.symon.Cpu;
+import com.loomcom.symon.CpuState;
 import com.loomcom.symon.machines.Machine;
 
 import javax.swing.*;
 import javax.swing.border.Border;
 import javax.swing.border.EtchedBorder;
 import java.awt.*;
-import java.awt.event.ActionEvent;
-import java.awt.event.ActionListener;
 
 /**
  * UI component that displays the current state of the simulated CPU.
@@ -277,7 +276,7 @@ public class StatusPanel extends JPanel {
      */
     public void updateState() {
         Cpu cpu = machine.getCpu();
-        Cpu.CpuState cpuState = cpu.getCpuState();
+        CpuState cpuState = cpu.getCpuState();
 
         // Update the Processor Status Flag display
         int status = cpuState.getStatusFlag();
@@ -293,7 +292,7 @@ public class StatusPanel extends JPanel {
         // Update the register and address displays
 
         // We always want to show the NEXT instruction that will be executed
-        opcodeField.setText(cpu.getCpuState().disassembleNextOp());
+        opcodeField.setText(cpu.disassembleNextOp());
         pcField.setText(cpu.getProgramCounterStatus());
         spField.setText(cpu.getStackPointerStatus());
         aField.setText(cpu.getAccumulatorStatus());

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

@@ -24,7 +24,7 @@
 
 package com.loomcom.symon.ui;
 
-import com.loomcom.symon.Cpu;
+import com.loomcom.symon.CpuState;
 import com.loomcom.symon.util.FifoRingBuffer;
 
 import javax.swing.*;
@@ -36,7 +36,7 @@ import java.awt.*;
  */
 public class TraceLog extends JFrame {
 
-    private final FifoRingBuffer<Cpu.CpuState> traceLog;
+    private final FifoRingBuffer<CpuState> traceLog;
     private final JTextArea                    traceLogTextArea;
 
     private static final Dimension MIN_SIZE       = new Dimension(320, 200);
@@ -71,7 +71,7 @@ public class TraceLog extends JFrame {
         StringBuilder logString = new StringBuilder();        
         
         synchronized(traceLog) {
-            for (Cpu.CpuState state : traceLog) {
+            for (CpuState state : traceLog) {
                 logString.append(state.toTraceEvent());
             }
         }
@@ -99,9 +99,9 @@ public class TraceLog extends JFrame {
      *
      * @param state The CPU State to append.
      */
-    public void append(Cpu.CpuState state) {
+    public void append(CpuState state) {
         synchronized(traceLog) {
-            traceLog.push(new Cpu.CpuState(state));
+            traceLog.push(new CpuState(state));
         }
     }
 

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

@@ -24,24 +24,9 @@
 package com.loomcom.symon.util;
 
 /**
- * Hex String Utilities.
+ * Various Utilities
- *
- * <p/>
- *
- * But why? Java, after all, has a number of ways to convert an integer into a hex string,
- * so it may look absurd to go to the trouble of writing yet another conversion! The answer is
- * performance.
- *
- * <p/>
- *
- * The most convenient way to get a formatted hex value from an integer is with the <code>String.format</code>
- * method, but this turns out to be extremely inefficient. Formatting a million integers
- * with <code>String.format</code> takes something like 1600ms. Formatting the same number of integers
- * with <code>HexUtil</code> takes only 160ms. This is on par with <code>Integer.toHexString</code>,
- * but also gives the desired padding.
- *
  */
-public class HexUtil {
+public class Utils {
 
     static final String NON_PRINTABLE = ".";
 
@@ -93,6 +78,7 @@ public class HexUtil {
 
     /**
      * Very fast 8-bit int to ASCII conversion.
+     *
      * @param val The value of an ASCII character.
      * @return A string representing the ASCII character.
      */
@@ -123,4 +109,11 @@ public class HexUtil {
     public static String wordToHex(int val) {
         return HEX_CONSTANTS[(val >> 8) & 0xff] + HEX_CONSTANTS[val & 0xff];
     }
+
+    /**
+     * Given two bytes, return an address.
+     */
+    public static int address(int lowByte, int hiByte) {
+        return ((hiByte << 8) | lowByte) & 0xffff;
+    }
 }

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

@@ -1,5 +1,6 @@
 package com.loomcom.symon;
 
+import com.loomcom.symon.util.Utils;
 import junit.framework.*;
 
 import com.loomcom.symon.devices.*;
@@ -537,11 +538,11 @@ public class CpuTest extends TestCase {
 
 
     public void testAddress() {
-        assertEquals(0xf1ea, cpu.address(0xea, 0xf1));
+        assertEquals(0xf1ea, Utils.address(0xea, 0xf1));
-        assertEquals(0x00ea, cpu.address(0xea, 0x00));
+        assertEquals(0x00ea, Utils.address(0xea, 0x00));
-        assertEquals(0xf100, cpu.address(0x00, 0xf1));
+        assertEquals(0xf100, Utils.address(0x00, 0xf1));
-        assertEquals(0x1234, cpu.address(0x34, 0x12));
+        assertEquals(0x1234, Utils.address(0x34, 0x12));
-        assertEquals(0xffff, cpu.address(0xff, 0xff));
+        assertEquals(0xffff, Utils.address(0xff, 0xff));
     }
 
     public void testZpxAddress() {

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

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

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

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