Release version 1.0.0

invoke setBus() on devices added to the bus

README.md

@@ -1,15 +1,9 @@
 SYMON - A 6502 System Simulator
 ===============================
 
-**NOTE: THIS SOFTWARE IS UNDER ACTIVE DEVELOPMENT. Feedback is welcome!**
+**Version:** 1.0.0
 
-**Version:** 0.9.9.0
-
-**Last Updated:** 26 July, 2014
-
-Copyright (c) 2014 Seth J. Morabito <web@loomcom.com>
-
-Portions Copyright (c) 2014 Maik Marten <maikmarten@googlemail.com>
+**Last Updated:** 11 August, 2014
 
 See the file COPYING for license.
 
@@ -31,6 +25,9 @@ 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
+are always welcome.
+
 ## 2.0 Requirements
 
   - Java 1.7 or higher
@@ -39,8 +36,9 @@ for more information about this functional test suite).
 
 ## 3.0 Features
 
-Symon can simiulate multiple 6502 based architectures. At present, two
-machines are implemented: Symon (the default), and MULTICOMP.
+Symon can simulate multiple 6502 based architectures. At present, three
+machines are implemented: Symon (the default), MULTICOMP, and a "Simple"
+machine useful for debugging.
 
 ### 3.1 Memory Maps
 
@@ -61,6 +59,10 @@ memory.
   - `$E000`--`$FFFF`: 8KB ROM
   - `$FFD0`--`$FFD1`: Motorola 6850 ACIA
 
+### 3.1.3 Simple Memory Map
+
+  - `$0000`--`$FFFF`: 64KB RAM
+
 ### 3.2 Serial Console and CPU Status
 
 ![Serial Console] (https://github.com/sethm/symon/raw/master/screenshots/console.png)
@@ -217,8 +219,16 @@ running.
 
 ## 5.0 Revision History
 
+  - **1.0.0-SNAPSHOT:** 10 August, 2014 - Added "Simple" machine
+    implementation, pure RAM with no IO. Added Klaus Dormann's
+    6502 Functional Tests for further machine verification (these
+    tests must be run in the "Simple" machine).
+
+  - **0.9.9.1:** 27 July, 2014 - Pressing 'Control' while clicking
+    'Reset' now performs a memory clear.
+
   - **0.9.9:** 26 July, 2014 - MULTICOMP and multi-machine support
-    contributed by Maik Marten <maikmarten@googlemail.com>
+    contributed by Maik Merten <maikmerten@googlemail.com>
 
   - **0.9.1:** 26 January, 2014 - Support for IRQ and NMI handling.
 
@@ -271,13 +281,20 @@ running.
 
   - Symbolic debugging.
 
-## 7.0 Acknowledgements
+## 7.0 Copyright and Acknowledgements
+
+**Copyright (c) 2014 Seth J. Morabito <web@loomcom.com>**
+
+Portions Copyright (c) 2014 Maik Merten <maikmerten@googlemail.com>
+
+Additional components used in this project are copyright their respective owners.
+
+  - Enhanced 6502 BASIC Copyright (c) Lee Davison
+  - 6502 Functional Tests Copyright (c) Klaus Dormann
+  - JTerminal Copyright (c) Graham Edgecombe
 
 This project would not have been possible without the following resources:
 
-  - [Graham Edgecombe's JTerminal project] (https://github.com/grahamedgecombe/jterminal),
-    which forms the core of Symon's console.
-
   - [Andrew Jacobs' 6502 Pages] (http://www.obelisk.demon.co.uk/6502/), for
     wonderfully detailed information about the 6502
 

pom.xml

@@ -4,7 +4,7 @@
     <groupId>com.loomcom.symon</groupId>
     <artifactId>symon</artifactId>
     <packaging>jar</packaging>
-    <version>0.9.9.0</version>
+    <version>1.0.0</version>
     <name>symon</name>
     <url>http://www.loomcom.com/symon</url>
     <properties>

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

@@ -113,6 +113,7 @@ public class Bus {
             deviceMap.put(priority, deviceSet);
         }
         
+        device.setBus(this);
         deviceSet.add(device);
         buildDeviceAddressArray();
     }

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

@@ -55,10 +55,6 @@ public class Cpu implements InstructionTable {
     public static final int IRQ_VECTOR_L = 0xfffe;
     public static final int IRQ_VECTOR_H = 0xffff;
 
-    // The delay in microseconds between steps.
-    // TODO: Make configurable
-    private static final int CLOCK_IN_NS = 1000;
-
     /* Simulated behavior */
     private static CpuBehavior behavior;
 
@@ -872,7 +868,7 @@ public class Cpu implements InstructionTable {
      */
     private int lsr(int m) {
         setCarryFlag((m & 0x01) != 0);
-        return (m >>> 1) & 0xff;
+        return (m & 0xff) >>> 1;
     }
 
     /**

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

@@ -26,6 +26,7 @@
 package com.loomcom.symon;
 
 import com.loomcom.symon.machines.MulticompMachine;
+import com.loomcom.symon.machines.SimpleMachine;
 import com.loomcom.symon.machines.SymonMachine;
 import java.util.Locale;
 import javax.swing.JOptionPane;
@@ -51,13 +52,15 @@ public class Main {
                     machineClass = SymonMachine.class;
                 } else if(machine.equals("multicomp")) {
                     machineClass = MulticompMachine.class;
+                } else if (machine.equals("simple")) {
+                    machineClass = SimpleMachine.class;
                 }
             }
         }
         
-        while(true) {        
-            if(machineClass == null) {
-                Object[] possibilities = {"Symon", "Multicomp"};
+        while (true) {
+            if (machineClass == null) {
+                Object[] possibilities = {"Symon", "Multicomp", "Simple"};
                 String s = (String)JOptionPane.showInputDialog(
                                 null,
                                 "Please choose the machine type to be emulated:",
@@ -67,9 +70,11 @@ public class Main {
                                 possibilities,
                                 "Symon");
                 
-                
-                if(s != null && s.equals("Multicomp")) {
+
+                if (s != null && s.equals("Multicomp")) {
                     machineClass = MulticompMachine.class;
+                } else if (s != null && s.equals("Simple")) {
+                    machineClass = SimpleMachine.class;
                 } else {
                     machineClass = SymonMachine.class;
                 }
@@ -91,13 +96,11 @@ public class Main {
         
         
             Simulator.MAIN_CMD cmd = simulator.waitForCommand();
-            if(cmd.equals(Simulator.MAIN_CMD.SELECTMACHINE)) {
+            if (cmd.equals(Simulator.MAIN_CMD.SELECTMACHINE)) {
                 machineClass = null;
             } else {
                 break;
             }
         }
-       
     }
-    
 }

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

@@ -110,7 +110,8 @@ public class Simulator {
 
     private JButton runStopButton;
     private JButton stepButton;
-    private JButton resetButton;
+    private JButton softResetButton;
+    private JButton hardResetButton;
     private JComboBox<String> stepCountBox;
 
     private JFileChooser      fileChooser;
@@ -137,13 +138,13 @@ public class Simulator {
      */
     public void createAndShowUi() throws IOException {
         mainWindow = new JFrame();
-        mainWindow.setTitle("Symon 6502 Simulator");
+        mainWindow.setTitle("6502 Simulator - " + machine.getName());
         mainWindow.setResizable(false);
         mainWindow.getContentPane().setLayout(new BorderLayout());
 
         // UI components used for I/O.
         this.console = new com.loomcom.symon.ui.Console(80, 25, DEFAULT_FONT);
-        this.statusPane = new StatusPanel();
+        this.statusPane = new StatusPanel(machine);
 
         console.setBorderWidth(CONSOLE_BORDER_WIDTH);
 
@@ -161,7 +162,8 @@ public class Simulator {
 
         runStopButton = new JButton("Run");
         stepButton = new JButton("Step");
-        resetButton = new JButton("Reset");
+        softResetButton = new JButton("Soft Reset");
+        hardResetButton = new JButton("Hard Reset");
 
         stepCountBox = new JComboBox<String>(STEPS);
         stepCountBox.addActionListener(new ActionListener() {
@@ -179,7 +181,8 @@ public class Simulator {
         buttonContainer.add(runStopButton);
         buttonContainer.add(stepButton);
         buttonContainer.add(stepCountBox);
-        buttonContainer.add(resetButton);
+        buttonContainer.add(softResetButton);
+        buttonContainer.add(hardResetButton);
 
         // Left side - console
         consoleContainer.add(console, BorderLayout.CENTER);
@@ -207,9 +210,17 @@ public class Simulator {
             }
         });
 
-        resetButton.addActionListener(new ActionListener() {
+        softResetButton.addActionListener(new ActionListener() {
             public void actionPerformed(ActionEvent actionEvent) {
-                handleReset();
+                // If this was a CTRL-click, do a hard reset.
+                handleReset(false);
+            }
+        });
+
+        hardResetButton.addActionListener(new ActionListener() {
+            public void actionPerformed(ActionEvent actionEvent) {
+                // If this was a CTRL-click, do a hard reset.
+                handleReset(true);
             }
         });
 
@@ -235,7 +246,7 @@ public class Simulator {
         mainWindow.setVisible(true);
 
         console.requestFocus();
-        handleReset();
+        handleReset(false);
     }
     
     public MAIN_CMD waitForCommand() {
@@ -268,7 +279,7 @@ public class Simulator {
     /*
      * Perform a reset.
      */
-    private void handleReset() {
+    private void handleReset(boolean isColdReset) {
         if (runLoop != null && runLoop.isRunning()) {
             runLoop.requestStop();
             runLoop.interrupt();
@@ -277,17 +288,24 @@ public class Simulator {
 
         try {
             logger.log(Level.INFO, "Reset requested. Resetting CPU.");
-            // Reset and clear memory
+            // Reset CPU
             machine.getCpu().reset();
             // Clear the console.
             console.reset();
             // Reset the trace log.
             traceLog.reset();
+            // If we're doing a cold reset, clear the memory.
+            if (isColdReset) {
+                Memory mem = machine.getRam();
+                if (mem != null) {
+                    mem.fill(0);
+                }
+            }
             // Update status.
             SwingUtilities.invokeLater(new Runnable() {
                 public void run() {
                     // Now update the state
-                    statusPane.updateState(machine.getCpu());
+                    statusPane.updateState();
                     memoryWindow.updateState();
                 }
             });
@@ -309,7 +327,7 @@ public class Simulator {
                     if (traceLog.isVisible()) {
                         traceLog.refresh();
                     }
-                    statusPane.updateState(machine.getCpu());
+                    statusPane.updateState();
                     memoryWindow.updateState();
                 }
             });
@@ -329,16 +347,15 @@ public class Simulator {
 
         // Read from the ACIA and immediately update the console if there's
         // output ready.
-        if (machine.getAcia().hasTxChar()) {
+        if (machine.getAcia() != null && machine.getAcia().hasTxChar()) {
             // This is thread-safe
             console.print(Character.toString((char) machine.getAcia().txRead()));
             console.repaint();
         }
 
         // If a key has been pressed, fill the ACIA.
-        // TODO: Interrupt handling.
         try {
-            if (console.hasInput()) {
+            if (machine.getAcia() != null && console.hasInput()) {
                 machine.getAcia().rxWrite((int) console.readInputChar());
             }
         } catch (FifoUnderrunException ex) {
@@ -356,7 +373,7 @@ public class Simulator {
             SwingUtilities.invokeLater(new Runnable() {
                 public void run() {
                     // Now update the state
-                    statusPane.updateState(machine.getCpu());
+                    statusPane.updateState();
                     memoryWindow.updateState();
                 }
             });
@@ -388,7 +405,7 @@ public class Simulator {
         SwingUtilities.invokeLater(new Runnable() {
             public void run() {
                 // Now update the state
-                statusPane.updateState(machine.getCpu());
+                statusPane.updateState();
                 memoryWindow.updateState();
             }
         });
@@ -435,7 +452,7 @@ public class Simulator {
 
             SwingUtilities.invokeLater(new Runnable() {
                 public void run() {
-                    statusPane.updateState(machine.getCpu());
+                    statusPane.updateState();
                     memoryWindow.updateState();
                     runStopButton.setText("Run");
                     stepButton.setEnabled(true);
@@ -445,7 +462,6 @@ public class Simulator {
                     }
                     menuBar.simulatorDidStop();
                     traceLog.simulatorDidStop();
-                    // TODO: Update memory window, if frame is visible.
                 }
             });
 
@@ -470,7 +486,6 @@ public class Simulator {
         }
 
         public void actionPerformed(ActionEvent actionEvent) {
-            // TODO: Error dialogs on failure.
             try {
                 int retVal = fileChooser.showOpenDialog(mainWindow);
                 if (retVal == JFileChooser.APPROVE_OPTION) {
@@ -479,7 +494,10 @@ public class Simulator {
                         long fileSize = f.length();
 
                         if (fileSize > machine.getMemorySize()) {
-                            throw new IOException("Program will not fit in available memory.");
+                            throw new IOException("File will not fit in " +
+                                    "available memory ($" +
+                                    Integer.toString(machine.getMemorySize(), 16) +
+                                    " bytes)");
                         } else {
                             byte[] program = new byte[(int) fileSize];
                             int i = 0;
@@ -498,13 +516,21 @@ public class Simulator {
 
                             // Now load the program at the starting address.
                             loadProgram(program, preferences.getProgramStartAddress());
+                            // TODO: "Don't Show Again" checkbox
+                            JOptionPane.showMessageDialog(mainWindow,
+                                    "Loaded Successfully At " +
+                                            String.format("$%04X", preferences.getProgramStartAddress()),
+                                    "OK",
+                                    JOptionPane.PLAIN_MESSAGE);
                         }
                     }
                 }
             } catch (IOException ex) {
                 logger.log(Level.SEVERE, "Unable to read program file: " + ex.getMessage());
+                JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             } catch (MemoryAccessException ex) {
                 logger.log(Level.SEVERE, "Memory access error loading program: " + ex.getMessage());
+                JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             }
         }
     }
@@ -517,7 +543,6 @@ public class Simulator {
         }
 
         public void actionPerformed(ActionEvent actionEvent) {
-            // TODO: Error dialogs on failure.
             try {
                 int retVal = fileChooser.showOpenDialog(mainWindow);
                 if (retVal == JFileChooser.APPROVE_OPTION) {
@@ -538,15 +563,24 @@ public class Simulator {
 
                             logger.log(Level.INFO, "ROM File `" + romFile.getName() + "' loaded at " +
                                                    String.format("0x%04X", machine.getRomBase()));
+                            // TODO: "Don't Show Again" checkbox
+                            JOptionPane.showMessageDialog(mainWindow,
+                                    "Loaded Successfully At " +
+                                            String.format("$%04X", machine.getRomBase()),
+                                    "OK",
+                                    JOptionPane.PLAIN_MESSAGE);
                         }
                     }
                 }
             } catch (IOException ex) {
                 logger.log(Level.SEVERE, "Unable to read ROM file: " + ex.getMessage());
+                JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             } catch (MemoryRangeException ex) {
                 logger.log(Level.SEVERE, "Memory range error while loading ROM file: " + ex.getMessage());
+                JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             } catch (MemoryAccessException ex) {
                 logger.log(Level.SEVERE, "Memory access error while loading ROM file: " + ex.getMessage());
+                JOptionPane.showMessageDialog(mainWindow, ex.getMessage(), "Failure", JOptionPane.ERROR_MESSAGE);
             }
         }
     }
@@ -564,8 +598,6 @@ public class Simulator {
     }
     
     class SelectMachineAction extends AbstractAction {
-        Simulator simulator;
-        
         public SelectMachineAction() {
             super("Switch emulated machine...", null);
             putValue(SHORT_DESCRIPTION, "Select the type of the machine to be emulated");
@@ -695,7 +727,9 @@ public class Simulator {
          */
         public void simulatorDidStart() {
             loadProgramItem.setEnabled(false);
-            loadRomItem.setEnabled(false);
+            if (loadRomItem != null) {
+                loadRomItem.setEnabled(false);
+            }
         }
 
         /**
@@ -703,7 +737,9 @@ public class Simulator {
          */
         public void simulatorDidStop() {
             loadProgramItem.setEnabled(true);
-            loadRomItem.setEnabled(true);
+            if (loadRomItem != null) {
+                loadRomItem.setEnabled(true);
+            }
         }
 
         private void initMenu() {
@@ -714,15 +750,22 @@ public class Simulator {
             JMenu fileMenu = new JMenu("File");
 
             loadProgramItem = new JMenuItem(new LoadProgramAction());
-            loadRomItem = new JMenuItem(new LoadRomAction());
-            JMenuItem prefsItem = new JMenuItem(new ShowPrefsAction());
-            JMenuItem selectMachineItem = new JMenuItem(new SelectMachineAction());
-            JMenuItem quitItem = new JMenuItem(new QuitAction());
-
             fileMenu.add(loadProgramItem);
-            fileMenu.add(loadRomItem);
+
+            // Simple Machine does not implement a ROM, so it makes no sense to
+            // offer a ROM load option.
+            if (machine.getRom() != null) {
+                loadRomItem = new JMenuItem(new LoadRomAction());
+                fileMenu.add(loadRomItem);
+            }
+
+            JMenuItem prefsItem = new JMenuItem(new ShowPrefsAction());
             fileMenu.add(prefsItem);
+
+            JMenuItem selectMachineItem = new JMenuItem(new SelectMachineAction());
             fileMenu.add(selectMachineItem);
+
+            JMenuItem quitItem = new JMenuItem(new QuitAction());
             fileMenu.add(quitItem);
 
             add(fileMenu);

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

@@ -56,5 +56,6 @@ public interface Machine {
     public int getRomSize();
     
     public int getMemorySize();
-    
+
+    String getName();
 }

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

@@ -147,5 +147,10 @@ public class MulticompMachine implements Machine {
     public int getMemorySize() {
         return MEMORY_SIZE;
     }
-    
+
+    @Override
+    public String getName() {
+        return "Multicomp";
+    }
+
 }

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

@@ -0,0 +1,93 @@
+package com.loomcom.symon.machines;
+
+import com.loomcom.symon.Bus;
+import com.loomcom.symon.Cpu;
+import com.loomcom.symon.devices.Acia;
+import com.loomcom.symon.devices.Crtc;
+import com.loomcom.symon.devices.Memory;
+import com.loomcom.symon.devices.Via;
+import com.loomcom.symon.exceptions.MemoryRangeException;
+
+/**
+ * A SimpleMachine is the simplest 6502 implementation possible - it
+ * consists solely of RAM and a CPU. This machine is primarily useful
+ * for running 6502 functional tests or debugging by hand.
+ */
+public class SimpleMachine implements Machine {
+
+    private static final int BUS_BOTTOM = 0x0000;
+    private static final int BUS_TOP    = 0xffff;
+
+    private final Bus bus;
+    private final Memory ram;
+    private final Cpu cpu;
+
+    public SimpleMachine() throws MemoryRangeException {
+        this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
+        this.ram = new Memory(BUS_BOTTOM, BUS_TOP, false);
+        this.cpu = new Cpu();
+
+        bus.addCpu(cpu);
+        bus.addDevice(ram);
+    }
+
+    @Override
+    public Bus getBus() {
+        return bus;
+    }
+
+    @Override
+    public Cpu getCpu() {
+        return cpu;
+    }
+
+    @Override
+    public Memory getRam() {
+        return ram;
+    }
+
+    @Override
+    public Acia getAcia() {
+        return null;
+    }
+
+    @Override
+    public Via getVia() {
+        return null;
+    }
+
+    @Override
+    public Crtc getCrtc() {
+        return null;
+    }
+
+    @Override
+    public Memory getRom() {
+        return null;
+    }
+
+    @Override
+    public void setRom(Memory rom) throws MemoryRangeException {
+        // No-op
+    }
+
+    @Override
+    public int getRomBase() {
+        return 0;
+    }
+
+    @Override
+    public int getRomSize() {
+        return 0;
+    }
+
+    @Override
+    public int getMemorySize() {
+        return BUS_TOP + 1;
+    }
+
+    @Override
+    public String getName() {
+        return "Simple";
+    }
+}

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

@@ -160,8 +160,11 @@ public class SymonMachine implements Machine {
     public int getMemorySize() {
         return MEMORY_SIZE;
     }
-    
-    
 
-    
+    @Override
+    public String getName() {
+        return "Symon";
+    }
+
+
 }

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

@@ -24,11 +24,17 @@
 package com.loomcom.symon.ui;
 
 import com.loomcom.symon.Cpu;
+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;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import java.util.regex.Pattern;
 
 /**
  * UI component that displays the current state of the simulated CPU.
@@ -73,14 +79,17 @@ public class StatusPanel extends JPanel {
     private JLabel xLabel;
     private JLabel yLabel;
 
+    private Machine machine;
+
     private static final int EMPTY_BORDER = 10;
     private static final Border LABEL_BORDER = BorderFactory.createEmptyBorder(0, 5, 0, 0);
     private static final Font LABEL_FONT = new Font(Font.SANS_SERIF, Font.BOLD, 12);
     private static final Dimension LARGE_TEXT_FIELD_SIZE = new Dimension(134, 22);
     private static final Dimension SMALL_TEXT_FIELD_SIZE = new Dimension(65, 22);
 
-    public StatusPanel() {
+    public StatusPanel(Machine machine) {
         super();
+        this.machine = machine;
         createUi();
     }
 
@@ -99,20 +108,20 @@ public class StatusPanel extends JPanel {
         JPanel statusFlagsPanel = new JPanel();
         statusFlagsPanel.setAlignmentX(LEFT_ALIGNMENT);
 
-        carryOn = new ImageIcon(this.getClass().getResource("images/C_on.png"));
-        carryOff = new ImageIcon(this.getClass().getResource("images/C_off.png"));
-        zeroOn = new ImageIcon(this.getClass().getResource("images/Z_on.png"));
-        zeroOff = new ImageIcon(this.getClass().getResource("images/Z_off.png"));
-        irqOn = new ImageIcon(this.getClass().getResource("images/I_on.png"));
-        irqOff = new ImageIcon(this.getClass().getResource("images/I_off.png"));
-        decimalOn = new ImageIcon(this.getClass().getResource("images/D_on.png"));
-        decimalOff = new ImageIcon(this.getClass().getResource("images/D_off.png"));
-        breakOn = new ImageIcon(this.getClass().getResource("images/B_on.png"));
-        breakOff = new ImageIcon(this.getClass().getResource("images/B_off.png"));
-        overflowOn = new ImageIcon(this.getClass().getResource("images/O_on.png"));
-        overflowOff = new ImageIcon(this.getClass().getResource("images/O_off.png"));
-        negativeOn = new ImageIcon(this.getClass().getResource("images/N_on.png"));
-        negativeOff = new ImageIcon(this.getClass().getResource("images/N_off.png"));
+        carryOn = new ImageIcon(this.getClass().getResource("/C_on.png"));
+        carryOff = new ImageIcon(this.getClass().getResource("/C_off.png"));
+        zeroOn = new ImageIcon(this.getClass().getResource("/Z_on.png"));
+        zeroOff = new ImageIcon(this.getClass().getResource("/Z_off.png"));
+        irqOn = new ImageIcon(this.getClass().getResource("/I_on.png"));
+        irqOff = new ImageIcon(this.getClass().getResource("/I_off.png"));
+        decimalOn = new ImageIcon(this.getClass().getResource("/D_on.png"));
+        decimalOff = new ImageIcon(this.getClass().getResource("/D_off.png"));
+        breakOn = new ImageIcon(this.getClass().getResource("/B_on.png"));
+        breakOff = new ImageIcon(this.getClass().getResource("/B_off.png"));
+        overflowOn = new ImageIcon(this.getClass().getResource("/O_on.png"));
+        overflowOff = new ImageIcon(this.getClass().getResource("/O_off.png"));
+        negativeOn = new ImageIcon(this.getClass().getResource("/N_on.png"));
+        negativeOff = new ImageIcon(this.getClass().getResource("/N_off.png"));
 
         // Initialize all to off
         carryFlagLabel = new JLabel(carryOff, JLabel.CENTER);
@@ -157,12 +166,83 @@ public class StatusPanel extends JPanel {
         pcLabel.setToolTipText("Program Counter");
         spLabel.setToolTipText("Stack Pointer");
 
-        opcodeField = makeTextField(LARGE_TEXT_FIELD_SIZE);
-        pcField = makeTextField(LARGE_TEXT_FIELD_SIZE);
-        spField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        aField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        xField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        yField = makeTextField(SMALL_TEXT_FIELD_SIZE);
+        opcodeField = makeTextField(LARGE_TEXT_FIELD_SIZE, false);
+        pcField = makeTextField(LARGE_TEXT_FIELD_SIZE, true);
+        spField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+        aField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+        xField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+        yField = makeTextField(SMALL_TEXT_FIELD_SIZE, true);
+
+        // Make fields editable
+        pcField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = getHexVal(pcField) & 0xffff;
+                    machine.getCpu().setProgramCounter(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                updateState();
+            }
+        });
+
+        spField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = getHexVal(spField) & 0xff;
+                    machine.getCpu().setStackPointer(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                updateState();
+            }
+        });
+
+        aField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = getHexVal(aField) & 0xff;
+                    machine.getCpu().setAccumulator(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                updateState();
+            }
+        });
+
+        xField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = getHexVal(xField) & 0xff;
+                    machine.getCpu().setXRegister(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                updateState();
+            }
+        });
+
+        yField.addActionListener(new ActionListener() {
+            @Override
+            public void actionPerformed(ActionEvent e) {
+                try {
+                    int newVal = getHexVal(yField) & 0xff;
+                    machine.getCpu().setYRegister(newVal);
+                } catch (Exception ex) {
+                    // Swallow exception
+                }
+
+                updateState();
+            }
+        });
 
         constraints.anchor = GridBagConstraints.LINE_START;
         constraints.gridwidth = 2;
@@ -220,14 +300,13 @@ public class StatusPanel extends JPanel {
 
     /**
      * Update the display based on the current state of the CPU.
-     *
-     * @param cpu The simulated 6502 CPU.
      */
-    public void updateState(Cpu cpu) {
+    public void updateState() {
+        Cpu cpu = machine.getCpu();
         Cpu.CpuState cpuState = cpu.getCpuState();
 
         // Update the Processor Status Flag display
-        int status = cpu.getCpuState().getStatusFlag();
+        int status = cpuState.getStatusFlag();
 
         carryFlagLabel.setIcon(iconForFlag(status, 0));
         zeroFlagLabel.setIcon(iconForFlag(status, 1));
@@ -313,10 +392,10 @@ public class StatusPanel extends JPanel {
         return label;
     }
 
-    private JTextField makeTextField(Dimension size) {
+    private JTextField makeTextField(Dimension size, boolean editable) {
         JTextField textField = new JTextField("");
         textField.setAlignmentX(LEFT_ALIGNMENT);
-        textField.setEditable(false);
+        textField.setEditable(editable);
         textField.setMinimumSize(size);
         textField.setMaximumSize(size);
         textField.setPreferredSize(size);
@@ -324,4 +403,8 @@ public class StatusPanel extends JPanel {
         return textField;
     }
 
+    private int getHexVal(JTextField source) throws NumberFormatException {
+        String val = source.getText().replaceAll("[^0-9a-fA-F]", "");
+        return Integer.parseInt(val, 16);
+    }
 }

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

@@ -583,4 +583,23 @@ public class CpuTest extends TestCase {
         cpu.setYRegister(0x95);
         assertEquals(0x15, cpu.zpyAddress(0x80));
     }
+
+    // Test for GitHub symon issue #9, "LSR can yield wrong result"
+    public void testRightShiftMasksBitsCorrectly() throws Exception {
+        // Illegal value, the accumulator should only care about the low 8 bytes.
+        // I'm a little uncomfortable with this test because really, setAccumulator should
+        // defensively mask the value, but does not. Is this relying on a bug to test another bug?
+        cpu.setAccumulator(0xff8);
+        // Sanity check, in case I ever change my mind on setAccumulator's behavior
+        assertEquals(0xff8, cpu.getAccumulator());
+
+        bus.loadProgram(0x4a,     // LSR
+                        0x4a);    // LSR
+
+        cpu.step();
+        assertEquals(0x7C, cpu.getAccumulator());
+
+        cpu.step();
+        assertEquals(0x3E, cpu.getAccumulator());
+    }
 }