New UI layout, ROM loading, Font selection

- The UI layout has changed, and will likely change again in the future.

- Symon can now re-load ROM images from the File menu, under "Load ROM..."

- Font size can be changed under the "View" menu

README.md

@@ -47,20 +47,33 @@ 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 1.5 or greater, just type:
 
-    $ java -jar symon-0.6-jar-with-dependencies.jar
+    $ java -jar symon-0.6-snapshot.jar
 
 When Symon is running, you should be presented with a simple graphical
 interface.
 
+### 3.2 ROM images
 
-### 3.2 Loading A Program
+The simulator requires a 16KB ROM image loaded at address $C000 to $FFFF to
+work properly. Without a ROM in memory, the simulator will not be able to
+reset, since the reset vector for the 6502 is located in this address space.
 
-Programs in the form of raw binary object files can be loaded directly
+By default, any 16KB file named 'rom.bin' that exists in the same directory
-into memory with the "Load" button.
+where Symon is launched will be loaded as a ROM image. ROM images can also
+be swapped out at run-time with the "Load ROM Image..." in the File menu.
 
-Right now, all programs are loaded starting at addres $0300.  After
+The "samples" directory contains a ROM image named 'ehbasic.rom', containing
-loading, the simulated CPU's reset vector is loaded with the values
+Lee Davison's Enhanced 6502 BASIC. This serves as a good starting point for
-$00, $03, and the CPU is reset.
+exploration.
+
+### 3.3 Loading A Program
+
+In addition to ROM images, programs in the form of raw binary object files can
+be loaded directly into memory from "Load Program..." in the File menu.
+
+Programs are loaded starting at addres $0300.  After loading the program, the
+simulated CPU's reset vector is loaded with the values $00, $03, and the CPU is
+reset.
 
 There are two very simple sample program in the "samples" directory,
 for testing.
@@ -69,33 +82,23 @@ for testing.
 
 - 'hello.prg' will continuously print "Hello, 6502 World!" to the console.
 
-The sample directory also contains a ROM image of Lee Davison's
-Ehanced 6502 BASIC. For instructions on loading the rom, please see
-the README file in that directory.
-
-### 3.3 ROM files
-
-Any 12KB file named 'rom.bin' that exists in the same directory where
-Symon is launched will be loaded at address $d000. If the file is
-larger than 12KB, loading will fail. This functionality will be
-improved in a future release!
-
 ### 3.4 Running
 
 After loading a program or ROM image, clicking "Run" will start the simulator
-running at address $0300.
+running.
-
 
 ## 4.0 To Do
 
+- Feedback (in the form of dialogs, status bar, etc).
+
+- Better ROM image handling
+
 - Better debugging tools from the UI, including memory inspection,
   disassembly, breakpoints, and execution tracing.
 
-- Better ROM loading (and re-loading)
-
 - More accurate timing.
   
-- Interrupt handling!
+- Smarter interrupt handling.
 
 - UI needs a ton more polish.
 
@@ -109,8 +112,6 @@ running at address $0300.
 
 - Implement CMOS 65C02 instructions and NMOS / CMOS mode flag.
 
-- Allow a flag to disable breaking to monitor on BRK.
-
 - Allow displaying ACIA status and dumping ACIA buffers, for
   debugging.
 

pom.xml

@@ -44,7 +44,7 @@
         <dependency>
             <groupId>com.grahamedgecombe.jterminal</groupId>
             <artifactId>jterminal</artifactId>
-            <version>1.0.2.1-loomcom</version>
+            <version>1.0.2.2-loomcom</version>
         </dependency>
     </dependencies>
 

samples/echo.asm

@@ -3,7 +3,7 @@
 ;;
 
 
-.alias iobase   $8000
+.alias iobase   $8800
 .alias iostatus [iobase + 1]
 .alias iocmd    [iobase + 2]
 .alias ioctrl   [iobase + 3]
@@ -11,7 +11,7 @@
 .org $0300
 
 start:  cli
-        lda #$09
+        lda #$0b
         sta iocmd      ; Set command status
         lda #$1a
         sta ioctrl     ; 0 stop bits, 8 bit word, 2400 baud

samples/ehbasic/min_mon.asm

@@ -37,10 +37,12 @@ RES_vec
 
 ; Initialize the ACIA
 ACIA_init
-	LDA	#$09
+	LDA	#$00
-	STA	ACIAcommand
+	STA	ACIAstatus		; Soft reset
-	LDA	#$1A			; Set output for 8-N-1 2400
+	LDA	#$0B
-	STA	ACIAcontrol
+	STA	ACIAcommand		; Parity disabled, IRQ disabled
+	LDA	#$1E
+	STA	ACIAcontrol		; Set output for 8-N-1 9600
 
 ; set up vectors and interrupt code, copy them to page 2
 
@@ -77,25 +79,33 @@ LAB_nokey
 LAB_dowarm
 	JMP	LAB_WARM		; do EhBASIC warm start
 
-; byte out to simulated ACIA
+; byte out to ACIA
 ACIAout
 	PHA				; save accumulator
-ACIAout_w
+@loop
 	LDA	ACIAstatus		; Read 6551 status
 	AND	#$10			; Is tx buffer full?
-	BEQ	ACIAout_w		; if not, loop back
+	BEQ	@loop			; if not, loop back
 	PLA				; Otherwise, restore accumulator
 	STA	ACIAdata		; write byte to 6551
 	RTS
 
-; byte in from simulated ACIA
+;
-
+; byte in from ACIA. This subroutine will also force
+; all lowercase letters to be uppercase.
+;
 ACIAin
 	LDA	ACIAstatus		; Read 6551 status
 	AND	#$08			;
 	BEQ	LAB_nobyw		; If rx buffer empty, no byte
 
 	LDA	ACIAdata		; Read byte from 6551
+	CMP	#'a'			; Is it < 'a'?
+	BCC	@done			; Yes, we're done
+	CMP	#'{'			; Is it >= '{'?
+	BCS	@done			; Yes, we're done
+	AND	#$5f			; Otherwise, mask to uppercase
+@done
 	SEC				; Flag byte received
 	RTS
 
@@ -137,16 +147,19 @@ NMI_CODE
 
 END_CODE
 
+; sign on string
+
 LAB_mess
-	.byte	$0D,$0A,"6502 EhBASIC [C]old/[W]arm ?",$00
+	.byte	$0D,$0A,"Symon 6502 SBC (c) 2012, Seth Morabito"
-					; sign on string
+	.byte   $0D,$0A,"[C]old/[W]arm ?",$00
+
 
 ; system vectors
 
 .segment "VECTORS"
 	.org	$FFFA
 
-	.word	0			; NMI vector
+	.word	NMI_vec		; NMI vector
 	.word	RES_vec		; RESET vector
-	.word	0			; IRQ vector
+	.word	IRQ_vec		; IRQ vector
 

samples/hello.asm

@@ -3,7 +3,7 @@
 ;;
 
 
-.alias iobase   $8000
+.alias iobase   $8800
 .alias iostatus [iobase + 1]
 .alias iocmd    [iobase + 2]
 .alias ioctrl   [iobase + 3]
@@ -11,7 +11,7 @@
 .org $0300
 
 start:  cli
-        lda #$09
+        lda #$0b
         sta iocmd      ; Set command status
         lda #$1a
         sta ioctrl     ; 0 stop bits, 8 bit word, 2400 baud

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

@@ -6,17 +6,17 @@ public interface Preferences {
 
     public static final int DEFAULT_PROGRAM_LOAD_ADDRESS = 0x0300;
 
-    public static final int DEFAULT_ACIA_ADDRESS = 0xc000;
-
     public static final int DEFAULT_BORDER_WIDTH = 10;
 
+    public static final boolean DEFAULT_HALT_ON_BREAK = true;
+
     public JDialog getDialog();
 
     public int getProgramStartAddress();
 
-    public int getAciaAddress();
-
     public int getBorderWidth();
 
+    public boolean getHaltOnBreak();
+
     public void updateUi();
 }

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

@@ -33,9 +33,9 @@ import com.loomcom.symon.exceptions.SymonException;
 import com.loomcom.symon.ui.Console;
 import com.loomcom.symon.ui.PreferencesDialog;
 import com.loomcom.symon.ui.StatusPanel;
-import sun.rmi.rmic.iiop.DirectoryLoader;
 
 import javax.swing.*;
+import javax.swing.border.EmptyBorder;
 import java.awt.*;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
@@ -55,7 +55,7 @@ import java.util.logging.Logger;
  * with a basic 80x25 character display.
  *
  */
-public class Simulator implements ActionListener, Observer {
+public class Simulator implements Observer {
 
     // Constants used by the simulated system. These define the memory map.
     private static final int BUS_BOTTOM = 0x0000;
@@ -75,6 +75,9 @@ public class Simulator implements ActionListener, Observer {
     private static final int ROM_BASE = 0xC000;
     private static final int ROM_SIZE = 0x4000;
 
+    private static final int DEFAULT_FONT_SIZE = 12;
+    private static final Font DEFAULT_FONT = new Font(Font.MONOSPACED, Font.PLAIN, DEFAULT_FONT_SIZE);
+
     // Since it is very expensive to update the UI with Swing's Event Dispatch Thread, we can't afford
     // to refresh the view on every simulated clock cycle. Instead, we will only refresh the view after this
     // number of steps when running normally.
@@ -100,25 +103,37 @@ public class Simulator implements ActionListener, Observer {
     // requested
     private int stepsSinceLastUpdate = 0;
 
-    private JFrame       mainWindow;
+    /**
-    private RunLoop      runLoop;
+     * The Main Window is the primary control point for the simulator.
-    private Console      console;
+     * It is in charge of the menu, and sub-windows. It also shows the
-    private StatusPanel  statusPane;
+     * CPU status at all times.
+     */
+    private JFrame mainWindow;
 
-    private JButton      runStopButton;
+    /**
-    private JButton      stepButton;
+     * The Console Window is connected to the ACIA's TX and RX lines.
-    private JButton      resetButton;
+     */
+    private JFrame consoleWindow;
 
-    // The most recently read key code
+    /**
-    private char         keyBuffer;
+     * The Trace Window shows the most recent 50,000 CPU states.
+     */
+    private JFrame traceWindow;
 
-    // TODO: loadProgramItem seriously violates encapsulation!
+    /**
-    // A far better solution would be to extend JMenu and add callback
+     * The Zero Page Window shows the contents of page 0.
-    // methods to enable and disable menus as required.
+     */
+    private JFrame zeroPageWindow;
 
-    // Menu Items
+    private SimulatorMenu menuBar;
-    private JMenuItem    loadProgramItem;
+
-    private JMenuItem    loadRomItem;
+    private RunLoop runLoop;
+    private Console console;
+    private StatusPanel statusPane;
+
+    private JButton runStopButton;
+    private JButton stepButton;
+    private JButton resetButton;
 
     private JFileChooser fileChooser;
     private PreferencesDialog  preferences;
@@ -154,10 +169,11 @@ public class Simulator implements ActionListener, Observer {
         mainWindow.getContentPane().setLayout(new BorderLayout());
 
         // The Menu
-        mainWindow.setJMenuBar(createMenuBar());
+        menuBar = new SimulatorMenu();
+        mainWindow.setJMenuBar(menuBar);
 
         // UI components used for I/O.
-        this.console = new com.loomcom.symon.ui.Console();
+        this.console = new com.loomcom.symon.ui.Console(80, 25, DEFAULT_FONT);
         this.statusPane = new StatusPanel();
 
         // File Chooser
@@ -166,15 +182,11 @@ public class Simulator implements ActionListener, Observer {
         preferences.addObserver(this);
 
         // Panel for Console and Buttons
-        JPanel controlsContainer = new JPanel();
+        JPanel consoleContainer = new JPanel();
         JPanel buttonContainer = new JPanel();
-        Dimension buttonPanelSize = new Dimension(console.getWidth(), 36);
 
-        buttonContainer.setMinimumSize(buttonPanelSize);
+        consoleContainer.setLayout(new BorderLayout());
-        buttonContainer.setMaximumSize(buttonPanelSize);
+        consoleContainer.setBorder(new EmptyBorder(10, 10, 10, 0));
-        buttonContainer.setPreferredSize(buttonPanelSize);
-
-        controlsContainer.setLayout(new BorderLayout());
         buttonContainer.setLayout(new FlowLayout());
 
         runStopButton = new JButton("Run");
@@ -186,8 +198,8 @@ public class Simulator implements ActionListener, Observer {
         buttonContainer.add(resetButton);
 
         // Left side - console
-        controlsContainer.add(console, BorderLayout.PAGE_START);
+        consoleContainer.add(console, BorderLayout.CENTER);
-        mainWindow.getContentPane().add(controlsContainer, BorderLayout.LINE_START);
+        mainWindow.getContentPane().add(consoleContainer, BorderLayout.LINE_START);
 
         // Right side - status pane
         mainWindow.getContentPane().add(statusPane, BorderLayout.LINE_END);
@@ -195,9 +207,27 @@ public class Simulator implements ActionListener, Observer {
         // Bottom - buttons.
         mainWindow.getContentPane().add(buttonContainer, BorderLayout.PAGE_END);
 
-        runStopButton.addActionListener(this);
+        runStopButton.addActionListener(new ActionListener() {
-        stepButton.addActionListener(this);
+            public void actionPerformed(ActionEvent actionEvent) {
-        resetButton.addActionListener(this);
+                if (runLoop != null && runLoop.isRunning()) {
+                    handleStop();
+                } else {
+                    handleStart();
+                }
+            }
+        });
+
+        stepButton.addActionListener(new ActionListener() {
+            public void actionPerformed(ActionEvent actionEvent) {
+                handleStep();
+            }
+        });
+
+        resetButton.addActionListener(new ActionListener() {
+            public void actionPerformed(ActionEvent actionEvent) {
+                handleReset();
+            }
+        });
 
         mainWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
@@ -207,78 +237,6 @@ public class Simulator implements ActionListener, Observer {
         mainWindow.setVisible(true);
     }
 
-    private JMenuBar createMenuBar() {
-        JMenuBar menuBar = new JMenuBar();
-
-        JMenu fileMenu = new JMenu("File");
-
-        menuBar.add(fileMenu);
-
-        loadProgramItem = new JMenuItem("Load Program");
-        loadProgramItem.setMnemonic(KeyEvent.VK_L);
-
-        loadRomItem = new JMenuItem("Load ROM...");
-        loadRomItem.setMnemonic(KeyEvent.VK_R);
-
-        JMenuItem prefsItem = new JMenuItem("Preferences...");
-        prefsItem.setMnemonic(KeyEvent.VK_P);
-
-        JMenuItem quitItem = new JMenuItem("Quit");
-        quitItem.setMnemonic(KeyEvent.VK_Q);
-
-        loadProgramItem.addActionListener(new ActionListener() {
-            public void actionPerformed(ActionEvent actionEvent) {
-                handleProgramLoad();
-            }
-        });
-
-        loadRomItem.addActionListener(new ActionListener() {
-            public void actionPerformed(ActionEvent actionEvent) {
-                handleRomLoad();
-            }
-        });
-
-        prefsItem.addActionListener(new ActionListener() {
-            public void actionPerformed(ActionEvent actionEvent) {
-                showAndUpdatePreferences();
-            }
-        });
-
-        quitItem.addActionListener(new ActionListener() {
-            public void actionPerformed(ActionEvent actionEvent) {
-                handleQuit();
-            }
-        });
-
-        fileMenu.add(loadProgramItem);
-        fileMenu.add(loadRomItem);
-        fileMenu.add(prefsItem);
-        fileMenu.add(quitItem);
-
-        return menuBar;
-    }
-
-    public void showAndUpdatePreferences() {
-        preferences.getDialog().setVisible(true);
-    }
-
-    /**
-     * Receive an ActionEvent from the UI, and act on it.
-     */
-    public void actionPerformed(ActionEvent actionEvent) {
-        if (actionEvent.getSource() == resetButton) {
-            coldReset();
-        } else if (actionEvent.getSource() == stepButton) {
-            handleStep();
-        } else if (actionEvent.getSource() == runStopButton) {
-            if (runLoop != null && runLoop.isRunning()) {
-                handleStop();
-            } else {
-                handleStart();
-            }
-        }
-    }
-
     private void handleStart() {
         // Shift focus to the console.
         console.requestFocus();
@@ -311,85 +269,10 @@ public class Simulator implements ActionListener, Observer {
         // TODO: Update memory window, if frame is visible.
     }
 
-    // TODO: Alert user of errors.
+    /*
-    private void handleRomLoad() {
+     * Perform a reset.
-        try {
-            int retVal = fileChooser.showOpenDialog(mainWindow);
-            if (retVal == JFileChooser.APPROVE_OPTION) {
-                File romFile = fileChooser.getSelectedFile();
-                if (romFile.canRead()) {
-                    long fileSize = romFile.length();
-
-                    if (fileSize != ROM_SIZE) {
-                        throw new IOException("ROM file must be exactly " + String.valueOf(fileSize) + " bytes.");
-                    } else {
-                        if (rom != null) {
-                            // Unload the existing ROM image.
-                            bus.removeDevice(rom);
-                        }
-                        // Load the new ROM image
-                        rom = Memory.makeROM(ROM_BASE, ROM_SIZE, romFile);
-                        bus.addDevice(rom);
-
-                        logger.log(Level.INFO, "ROM File `" + romFile.getName() + "' loaded at " +
-                                               String.format("0x%04X", ROM_BASE));
-                    }
-                }
-            }
-        } catch (IOException ex) {
-            logger.log(Level.SEVERE, "Unable to read file: " + ex.getMessage());
-            ex.printStackTrace();
-        } catch (MemoryRangeException ex) {
-            logger.log(Level.SEVERE, "Memory range error loading ROM");
-            ex.printStackTrace();
-        }
-    }
-
-    /**
-     * Display a file chooser prompting the user to load a binary program.
-     * After the user selects a file, read it in starting at PROGRAM_START_ADDRESS.
      */
-    private void handleProgramLoad() {
+    private void handleReset() {
-        try {
-            int retVal = fileChooser.showOpenDialog(mainWindow);
-            if (retVal == JFileChooser.APPROVE_OPTION) {
-                File f = fileChooser.getSelectedFile();
-                if (f.canRead()) {
-                    long fileSize = f.length();
-
-                    if (fileSize > MEMORY_SIZE) {
-                        throw new IOException("Program will not fit in available memory.");
-                    } else {
-                        byte[] program = new byte[(int) fileSize];
-                        int i = 0;
-                        FileInputStream fis = new FileInputStream(f);
-                        BufferedInputStream bis = new BufferedInputStream(fis);
-                        DataInputStream dis = new DataInputStream(bis);
-                        while (dis.available() != 0) {
-                            program[i++] = dis.readByte();
-                        }
-
-                        SwingUtilities.invokeLater(new Runnable() {
-                            public void run() {
-                                console.reset();
-                            }
-                        });
-
-                        // Now load the program at the starting address.
-                        loadProgram(program, preferences.getProgramStartAddress());
-                    }
-                }
-            }
-        } catch (IOException ex) {
-            logger.log(Level.SEVERE, "Unable to read file: " + ex.getMessage());
-            ex.printStackTrace();
-        } catch (MemoryAccessException ex) {
-            logger.log(Level.SEVERE, "Memory access error loading program");
-            ex.printStackTrace();
-        }
-    }
-
-    private void coldReset() {
         if (runLoop != null && runLoop.isRunning()) {
             runLoop.requestStop();
             runLoop.interrupt();
@@ -412,7 +295,6 @@ public class Simulator implements ActionListener, Observer {
             });
         } catch (MemoryAccessException ex) {
             logger.log(Level.SEVERE, "Exception during simulator reset: " + ex.getMessage());
-            ex.printStackTrace();
         }
     }
 
@@ -429,17 +311,6 @@ public class Simulator implements ActionListener, Observer {
         }
     }
 
-    /**
-     * Handle a request to quit.
-     */
-    private void handleQuit() {
-        if (runLoop != null && runLoop.isRunning()) {
-            runLoop.requestStop();
-            runLoop.interrupt();
-        }
-        System.exit(0);
-    }
-
     /**
      * Perform a single step of the simulated system.
      */
@@ -516,7 +387,7 @@ public class Simulator implements ActionListener, Observer {
                     Simulator simulator = new Simulator();
                     simulator.createAndShowUi();
                     // Reset the simulator.
-                    simulator.coldReset();
+                    simulator.handleReset();
                 } catch (Exception e) {
                     e.printStackTrace();
                 }
@@ -533,8 +404,6 @@ public class Simulator implements ActionListener, Observer {
     public void update(Observable observable, Object o) {
         // Instance equality should work here, there is only one instance.
         if (observable == preferences) {
-            // TODO: Update ACIA base address if it has changed.
-
             int oldBorderWidth = console.getBorderWidth();
             if (oldBorderWidth != preferences.getBorderWidth()) {
                 // Resize the main window if the border width has changed.
@@ -544,7 +413,6 @@ public class Simulator implements ActionListener, Observer {
         }
     }
 
-
     /**
      * The main run thread.
      */
@@ -569,16 +437,14 @@ public class Simulator implements ActionListener, Observer {
                     console.startListening();
                     // Don't allow step while the simulator is running
                     stepButton.setEnabled(false);
-                    loadProgramItem.setEnabled(false);
+                    menuBar.simulatorDidStart();
-                    loadRomItem.setEnabled(false);
                     // Toggle the state of the run button
                     runStopButton.setText("Stop");
                 }
             });
 
             try {
-                // TODO: Interrupts - both software and hardware. i.e., jump to address stored in FFFE/FFFF on BRK.
+                while (isRunning && !(preferences.getHaltOnBreak() && cpu.getBreakFlag())) {
-                while (isRunning && !cpu.getBreakFlag()) {
                     step();
                 }
             } catch (SymonException ex) {
@@ -591,16 +457,235 @@ public class Simulator implements ActionListener, Observer {
                     console.stopListening();
                     // Allow step while the simulator is stopped
                     stepButton.setEnabled(true);
-                    loadProgramItem.setEnabled(true);
+                    menuBar.simulatorDidStop();
-                    loadRomItem.setEnabled(true);
                     runStopButton.setText("Run");
                     // Now update the state
                     statusPane.updateState(cpu);
                 }
             });
 
-            logger.log(Level.INFO, "Exiting main run loop. BREAK=" + cpu.getBreakBit() + "; RUN_FLAG=" + isRunning);
             isRunning = false;
         }
     }
+
+    class LoadProgramAction extends AbstractAction {
+        public LoadProgramAction() {
+            super("Load Program...", null);
+            putValue(SHORT_DESCRIPTION, "Load a program into memory");
+            putValue(MNEMONIC_KEY, KeyEvent.VK_L);
+        }
+
+        public void actionPerformed(ActionEvent actionEvent) {
+            // TODO: Error dialogs on failure.
+            try {
+                int retVal = fileChooser.showOpenDialog(mainWindow);
+                if (retVal == JFileChooser.APPROVE_OPTION) {
+                    File f = fileChooser.getSelectedFile();
+                    if (f.canRead()) {
+                        long fileSize = f.length();
+
+                        if (fileSize > MEMORY_SIZE) {
+                            throw new IOException("Program will not fit in available memory.");
+                        } else {
+                            byte[] program = new byte[(int) fileSize];
+                            int i = 0;
+                            FileInputStream fis = new FileInputStream(f);
+                            BufferedInputStream bis = new BufferedInputStream(fis);
+                            DataInputStream dis = new DataInputStream(bis);
+                            while (dis.available() != 0) {
+                                program[i++] = dis.readByte();
+                            }
+
+                            SwingUtilities.invokeLater(new Runnable() {
+                                public void run() {
+                                    console.reset();
+                                }
+                            });
+
+                            // Now load the program at the starting address.
+                            loadProgram(program, preferences.getProgramStartAddress());
+                        }
+                    }
+                }
+            } catch (IOException ex) {
+                logger.log(Level.SEVERE, "Unable to read program file: " + ex.getMessage());
+            } catch (MemoryAccessException ex) {
+                logger.log(Level.SEVERE, "Memory access error loading program: " + ex.getMessage());
+            }
+        }
+    }
+
+    class LoadRomAction extends AbstractAction {
+        public LoadRomAction() {
+            super("Load ROM...", null);
+            putValue(SHORT_DESCRIPTION, "Load a ROM image");
+            putValue(MNEMONIC_KEY, KeyEvent.VK_R);
+        }
+
+        public void actionPerformed(ActionEvent actionEvent) {
+            // TODO: Error dialogs on failure.
+            try {
+                int retVal = fileChooser.showOpenDialog(mainWindow);
+                if (retVal == JFileChooser.APPROVE_OPTION) {
+                    File romFile = fileChooser.getSelectedFile();
+                    if (romFile.canRead()) {
+                        long fileSize = romFile.length();
+
+                        if (fileSize != ROM_SIZE) {
+                            throw new IOException("ROM file must be exactly " + String.valueOf(ROM_SIZE) + " bytes.");
+                        } else {
+                            if (rom != null) {
+                                // Unload the existing ROM image.
+                                bus.removeDevice(rom);
+                            }
+                            // Load the new ROM image
+                            rom = Memory.makeROM(ROM_BASE, ROM_SIZE, romFile);
+                            bus.addDevice(rom);
+
+                            // Now, reset
+                            cpu.reset();
+
+                            logger.log(Level.INFO, "ROM File `" + romFile.getName() + "' loaded at " +
+                                                   String.format("0x%04X", ROM_BASE));
+                        }
+                    }
+                }
+            } catch (IOException ex) {
+                logger.log(Level.SEVERE, "Unable to read ROM file: " + ex.getMessage());
+            } catch (MemoryRangeException ex) {
+                logger.log(Level.SEVERE, "Memory range error while loading ROM file: " + ex.getMessage());
+            } catch (MemoryAccessException ex) {
+                logger.log(Level.SEVERE, "Memory access error while loading ROM file: " + ex.getMessage());
+            }
+        }
+    }
+
+    class ShowPrefsAction extends AbstractAction {
+        public ShowPrefsAction() {
+            super("Preferences...", null);
+            putValue(SHORT_DESCRIPTION, "Show Preferences Dialog");
+            putValue(MNEMONIC_KEY, KeyEvent.VK_P);
+        }
+
+        public void actionPerformed(ActionEvent actionEvent) {
+            preferences.getDialog().setVisible(true);
+        }
+    }
+
+    class QuitAction extends AbstractAction {
+        public QuitAction() {
+            super("Quit", null);
+            putValue(SHORT_DESCRIPTION, "Exit the Simulator");
+            putValue(MNEMONIC_KEY, KeyEvent.VK_Q);
+        }
+
+        public void actionPerformed(ActionEvent actionEvent) {
+            if (runLoop != null && runLoop.isRunning()) {
+                runLoop.requestStop();
+                runLoop.interrupt();
+            }
+            System.exit(0);
+        }
+    }
+
+    class SetFontAction extends AbstractAction {
+        private int size;
+
+        public SetFontAction(int size) {
+            super(Integer.toString(size) + " pt", null);
+            this.size = size;
+            putValue(SHORT_DESCRIPTION, "Set font to " + Integer.toString(size) + "pt.");
+        }
+
+        public void actionPerformed(ActionEvent actionEvent) {
+            SwingUtilities.invokeLater(new Runnable() {
+                public void run() {
+                    console.setFont(new Font("Monospaced", Font.PLAIN, size));
+                    mainWindow.pack();
+                }
+            });
+        }
+    }
+
+    class SimulatorMenu extends JMenuBar {
+        // Menu Items
+        private JMenuItem    loadProgramItem;
+        private JMenuItem    loadRomItem;
+
+        /**
+         * Create a new SimulatorMenu instance.
+         */
+        public SimulatorMenu() {
+            initMenu();
+        }
+
+        /**
+         * Disable menu items that should not be available during simulator execution.
+         */
+        public void simulatorDidStart() {
+            loadProgramItem.setEnabled(false);
+            loadRomItem.setEnabled(false);
+        }
+
+        /**
+         * Enable menu items that should be available while the simulator is stopped.
+         */
+        public void simulatorDidStop() {
+            loadProgramItem.setEnabled(true);
+            loadRomItem.setEnabled(true);
+        }
+
+        private void initMenu() {
+            /*
+             * File Menu
+             */
+
+            JMenu fileMenu = new JMenu("File");
+
+            loadProgramItem = new JMenuItem(new LoadProgramAction());
+            loadRomItem = new JMenuItem(new LoadRomAction());
+            JMenuItem prefsItem = new JMenuItem(new ShowPrefsAction());
+            JMenuItem quitItem = new JMenuItem(new QuitAction());
+
+            fileMenu.add(loadProgramItem);
+            fileMenu.add(loadRomItem);
+            fileMenu.add(prefsItem);
+            fileMenu.add(quitItem);
+
+            add(fileMenu);
+
+            /*
+             * View Menu
+             */
+
+            JMenu viewMenu = new JMenu("View");
+            JMenu fontSubMenu = new JMenu("Font Size");
+            ButtonGroup group = new ButtonGroup();
+
+            makeFontSizeMenuItem(10, fontSubMenu, group);
+            makeFontSizeMenuItem(11, fontSubMenu, group);
+            makeFontSizeMenuItem(12, fontSubMenu, group);
+            makeFontSizeMenuItem(13, fontSubMenu, group);
+            makeFontSizeMenuItem(14, fontSubMenu, group);
+            makeFontSizeMenuItem(15, fontSubMenu, group);
+            makeFontSizeMenuItem(16, fontSubMenu, group);
+            makeFontSizeMenuItem(17, fontSubMenu, group);
+            makeFontSizeMenuItem(18, fontSubMenu, group);
+            makeFontSizeMenuItem(19, fontSubMenu, group);
+            makeFontSizeMenuItem(20, fontSubMenu, group);
+
+            viewMenu.add(fontSubMenu);
+            add(viewMenu);
+        }
+
+        private void makeFontSizeMenuItem(int size, JMenu fontSubMenu, ButtonGroup group) {
+            Action action = new SetFontAction(size);
+
+            JRadioButtonMenuItem item = new JRadioButtonMenuItem(action);
+            item.setSelected(size == DEFAULT_FONT_SIZE);
+            fontSubMenu.add(item);
+            group.add(item);
+        }
+    }
+
 }

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

@@ -170,8 +170,8 @@ public class Acia extends Device {
      */
     private long calculateBaudRateDelay() {
         if (baudRate > 0) {
-            // This is a pretty rough approximation based on 8 bits per character,
+            // TODO: This is a pretty rough approximation based on 8 bits per character,
-            // and 1/baudRate per bit.
+            // and 1/baudRate per bit. It could certainly be improved
             return (long)((1.0 / baudRate) * 1000000000 * 8);
         } else {
             return 0;

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

@@ -1,5 +1,6 @@
 package com.loomcom.symon.ui;
 
+import java.awt.*;
 import java.awt.event.KeyEvent;
 import java.awt.event.KeyListener;
 import java.awt.event.MouseEvent;
@@ -36,12 +37,8 @@ public class Console extends JTerminal implements KeyListener, MouseListener {
 
     private FifoRingBuffer<Character> typeAheadBuffer;
 
-    public Console() {
+    public Console(int columns, int rows, Font font) {
-        this(DEFAULT_COLUMNS, DEFAULT_ROWS);
+        super(new Vt100TerminalModel(columns, rows), font);
-    }
-
-    public Console(int columns, int rows) {
-        super(new Vt100TerminalModel(columns, rows));
         // A small type-ahead buffer, as might be found in any real
         // VT100-style serial terminal.
         this.typeAheadBuffer = new FifoRingBuffer<Character>(128);

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

@@ -12,13 +12,13 @@ public class PreferencesDialog extends Observable implements Preferences {
 
     private final JDialog dialog;
 
-    private JTextField aciaAddressField;
+    private JCheckBox  haltOnBreakCheckBox;
     private JTextField programLoadAddressField;
     private JTextField borderWidthField;
 
     private int programLoadAddress = DEFAULT_PROGRAM_LOAD_ADDRESS;
-    private int aciaAddress = DEFAULT_ACIA_ADDRESS;
     private int borderWidth = DEFAULT_BORDER_WIDTH;
+    private boolean haltOnBreak = DEFAULT_HALT_ON_BREAK;
 
     public PreferencesDialog(Frame parent, boolean modal) {
         this.dialog = new JDialog(parent, modal);
@@ -43,15 +43,14 @@ public class PreferencesDialog extends Observable implements Preferences {
         GridBagLayout layout = new GridBagLayout();
         settingsContainer.setLayout(layout);
 
-        final JLabel aciaAddressLabel = new JLabel("ACIA Address");
+        final JLabel haltOnBreakLabel = new JLabel("Halt on BRK");
         final JLabel programLoadAddressLabel = new JLabel("Program Load Address");
         final JLabel borderWidthLabel = new JLabel("Console Border Width");
 
-        aciaAddressField = new JTextField(8);
+        haltOnBreakCheckBox = new JCheckBox();
         programLoadAddressField = new JTextField(8);
         borderWidthField = new JTextField(8);
 
-        aciaAddressLabel.setLabelFor(aciaAddressField);
         programLoadAddressLabel.setLabelFor(programLoadAddressField);
         borderWidthLabel.setLabelFor(borderWidthField);
 
@@ -61,11 +60,10 @@ public class PreferencesDialog extends Observable implements Preferences {
         constraints.fill = GridBagConstraints.HORIZONTAL;
         constraints.gridx = 0;
         constraints.gridy = 0;
-
+        settingsContainer.add(haltOnBreakLabel, constraints);
-        settingsContainer.add(aciaAddressLabel, constraints);
 
         constraints.gridx = 1;
-        settingsContainer.add(aciaAddressField, constraints);
+        settingsContainer.add(haltOnBreakCheckBox, constraints);
 
         constraints.gridy = 1;
         constraints.gridx = 0;
@@ -94,8 +92,8 @@ public class PreferencesDialog extends Observable implements Preferences {
 
         applyButton.addActionListener(new ActionListener() {
             public void actionPerformed(ActionEvent actionEvent) {
+                haltOnBreak = haltOnBreakCheckBox.isSelected();
                 programLoadAddress = hexToInt(programLoadAddressField.getText());
-                aciaAddress = hexToInt(aciaAddressField.getText());
                 borderWidth = Integer.parseInt(borderWidthField.getText());
                 updateUi();
                 // TODO: Actually check to see if values have changed, don't assume.
@@ -118,10 +116,6 @@ public class PreferencesDialog extends Observable implements Preferences {
         return programLoadAddress;
     }
 
-    public int getAciaAddress() {
-        return aciaAddress;
-    }
-
     /**
      * @return The width of the console border, in pixels.
      */
@@ -129,8 +123,15 @@ public class PreferencesDialog extends Observable implements Preferences {
         return borderWidth;
     }
 
+    /**
+     * @return True if 'halt on break' is desired, false otherwise.
+     */
+    public boolean getHaltOnBreak() {
+        return haltOnBreak;
+    }
+
     public void updateUi() {
-        aciaAddressField.setText(intToHex(aciaAddress));
+        haltOnBreakCheckBox.setSelected(haltOnBreak);
         programLoadAddressField.setText(intToHex(programLoadAddress));
         borderWidthField.setText(Integer.toString(borderWidth));
     }

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

@@ -26,6 +26,7 @@ public class StatusPanel extends JPanel {
     private final ImageIcon negativeOn;
     private final ImageIcon negativeOff;
 
+    private final JLabel statusFlagsLabel;
     private final JLabel carryFlagLabel;
     private final JLabel zeroFlagLabel;
     private final JLabel irqDisableFlagLabel;
@@ -40,7 +41,6 @@ public class StatusPanel extends JPanel {
     private JTextField aField;
     private JTextField xField;
     private JTextField yField;
-//    private JTextField stepCountField;
 
     private final JLabel opcodeLabel;
     private final JLabel pcLabel;
@@ -48,11 +48,10 @@ public class StatusPanel extends JPanel {
     private final JLabel aLabel;
     private final JLabel xLabel;
     private final JLabel yLabel;
-//    private final JLabel stepCountLabel;
 
-    private static final int EMPTY_BORDER = 5;
+    private static final int EMPTY_BORDER = 10;
-    private static final Border LABEL_BORDER = BorderFactory.createEmptyBorder(0, 4, 0, 0);
+    private static final Border LABEL_BORDER = BorderFactory.createEmptyBorder(0, 5, 0, 0);
-    private static final Font LABEL_FONT = new Font("sansserif", Font.PLAIN, 11);
+    private static final Font LABEL_FONT = new Font(Font.SANS_SERIF, Font.BOLD, 12);
 
     public StatusPanel() {
         super();
@@ -63,7 +62,10 @@ public class StatusPanel extends JPanel {
 
         setBorder(BorderFactory.createCompoundBorder(emptyBorder, etchedBorder));
 
-        setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
+        GridBagLayout layout = new GridBagLayout();
+        GridBagConstraints constraints = new GridBagConstraints();
+
+        setLayout(layout);
 
         JPanel statusFlagsPanel = new JPanel();
         statusFlagsPanel.setAlignmentX(LEFT_ALIGNMENT);
@@ -101,37 +103,72 @@ public class StatusPanel extends JPanel {
         statusFlagsPanel.add(carryFlagLabel);
 
         // Create and add register and address labels
-        opcodeLabel = makeLabel("Instruction");
+        statusFlagsLabel = makeLabel("Flags");
-        pcLabel = makeLabel("Program Counter");
+        opcodeLabel = makeLabel("IR");
-        spLabel = makeLabel("Stack Pointer");
+        pcLabel = makeLabel("PC");
-        aLabel = makeLabel("Accumulator");
+        spLabel = makeLabel("SP");
-        xLabel = makeLabel("X Register");
+        aLabel = makeLabel("A");
-        yLabel = makeLabel("Y Register");
+        xLabel = makeLabel("X");
-//        stepCountLabel = new JLabel("Steps");
+        yLabel = makeLabel("Y");
 
-        opcodeField = makeTextField();
+        opcodeField = makeTextField(LARGE_TEXT_FIELD_SIZE);
-        pcField = makeTextField();
+        pcField = makeTextField(LARGE_TEXT_FIELD_SIZE);
-        spField = makeTextField();
+        spField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        aField = makeTextField();
+        aField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        xField = makeTextField();
+        xField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-        yField = makeTextField();
+        yField = makeTextField(SMALL_TEXT_FIELD_SIZE);
-//        stepCountField = new JTextField("");
 
-        add(statusFlagsPanel);
+        constraints.anchor = GridBagConstraints.LINE_START;
-        add(opcodeLabel);
+        constraints.gridwidth = 2;
-        add(opcodeField);
+        constraints.gridx = 0;
-        add(pcLabel);
+        constraints.gridy = 0;
-        add(pcField);
+        add(statusFlagsLabel, constraints);
-        add(spLabel);
+        constraints.gridy = 1;
-        add(spField);
+        add(statusFlagsPanel, constraints);
-        add(aLabel);
+
-        add(aField);
+        constraints.insets = new Insets(5, 0, 0, 0);
-        add(xLabel);
+        constraints.gridy = 2;
-        add(xField);
+        add(opcodeLabel, constraints);
-        add(yLabel);
+
-        add(yField);
+        constraints.insets = new Insets(0, 0, 0, 0);
-//        add(stepCountLabel);
+        constraints.gridy = 3;
-//        add(stepCountField);
+        add(opcodeField, constraints);
+
+        constraints.insets = new Insets(5, 0, 0, 0);
+        constraints.gridy = 4;
+        add(pcLabel, constraints);
+
+        constraints.insets = new Insets(0, 0, 0, 0);
+        constraints.gridy = 5;
+        add(pcField, constraints);
+
+        constraints.insets = new Insets(5, 0, 0, 0);
+        constraints.gridwidth = 1;
+        constraints.gridy = 6;
+        add(spLabel, constraints);
+        constraints.gridx = 1;
+        add(aLabel, constraints);
+
+        constraints.insets = new Insets(0, 0, 0, 0);
+        constraints.gridx = 0;
+        constraints.gridy = 7;
+        add(spField, constraints);
+        constraints.gridx = 1;
+        add(aField, constraints);
+
+        constraints.insets = new Insets(5, 0, 0, 0);
+        constraints.gridx = 0;
+        constraints.gridy = 8;
+        add(yLabel, constraints);
+        constraints.gridx = 1;
+        add(xLabel, constraints);
+
+        constraints.insets = new Insets(0, 0, 5, 0);
+        constraints.gridx = 0;
+        constraints.gridy = 9;
+        add(xField, constraints);
+        constraints.gridx = 1;
+        add(yField, constraints);
     }
 
     /**
@@ -158,7 +195,6 @@ public class StatusPanel extends JPanel {
         aField.setText(cpu.getAccumulatorStatus());
         xField.setText(cpu.getXRegisterStatus());
         yField.setText(cpu.getYRegisterStatus());
-//        stepCountField.setText(Long.toString(cpu.getStepCounter()));
 
         repaint();
     }
@@ -228,10 +264,16 @@ public class StatusPanel extends JPanel {
         return label;
     }
 
-    private JTextField makeTextField() {
+    private static final Dimension LARGE_TEXT_FIELD_SIZE = new Dimension(134, 22);
+    private static final Dimension SMALL_TEXT_FIELD_SIZE = new Dimension(65, 22);
+
+    private JTextField makeTextField(Dimension size) {
         JTextField textField = new JTextField("");
         textField.setAlignmentX(LEFT_ALIGNMENT);
         textField.setEditable(false);
+        textField.setMinimumSize(size);
+        textField.setMaximumSize(size);
+        textField.setPreferredSize(size);
         return textField;
     }