Cleaner simulator startup and run-loop exiting

- If a default ROM image ("rom.bin") isn't available at startup, the
  simulator will now create and load a 16KB R/W memory at the ROM
  location, so resets will work even without a ROM loaded.

- Cleaned up the way simulator UI state is updated when the run loop
  exits.

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

@@ -49,12 +49,11 @@ import java.util.logging.Logger;
 
 /**
  * Symon Simulator Interface and Control.
- *
+ * <p/>
  * This class provides a control and I/O system for the simulated 6502 system.
  * It includes the simulated CPU itself, as well as 32KB of RAM, 16KB of ROM,
  * and a simulated ACIA for serial I/O. The ACIA is attached to a dumb terminal
  * with a basic 80x25 character display.
- *
  */
 public class Simulator implements Observer {
 
@@ -156,8 +155,12 @@ public class Simulator implements Observer {
         if (romImage.canRead()) {
             logger.info("Loading ROM image from file " + romImage);
             this.rom = Memory.makeROM(ROM_BASE, ROM_SIZE, romImage);
-            bus.addDevice(rom);
+        } else {
+            logger.info("Default ROM file " + romImage +
+                        " not found, loading empty R/W memory image.");
+            this.rom = Memory.makeRAM(ROM_BASE, ROM_SIZE);
         }
+        bus.addDevice(rom);
     }
 
     /**
@@ -254,26 +257,6 @@ public class Simulator implements Observer {
         runLoop.requestStop();
         runLoop.interrupt();
         runLoop = null;
-        simulatorDidStop();
-    }
-
-    /*
-     * Handle post-stop actions.
-     */
-    private void simulatorDidStop() {
-        // The simulator is lazy about updating the UI for performance reasons, so always request an
-        // immediate update after stopping.
-        SwingUtilities.invokeLater(new Runnable() {
-            public void run() {
-                // Now update the state
-                statusPane.updateState(cpu);
-            }
-        });
-        traceLog.simulatorDidStop();
-        if (traceLog.isVisible()) {
-            traceLog.refresh();
-        }
-        // TODO: Update memory window, if frame is visible.
     }
 
     /*
@@ -313,7 +296,9 @@ public class Simulator implements Observer {
     private void handleStep() {
         try {
             step();
-            simulatorDidStop();
+            if (traceLog.isVisible()) {
+                traceLog.refresh();
+            }
         } catch (SymonException ex) {
             logger.log(Level.SEVERE, "Exception during simulator step: " + ex.getMessage());
             ex.printStackTrace();
@@ -389,22 +374,6 @@ public class Simulator implements Observer {
         });
     }
 
-    public static void main(String args[]) {
-        SwingUtilities.invokeLater(new Runnable() {
-            public void run() {
-                try {
-                    // Create the main UI window
-                    Simulator simulator = new Simulator();
-                    simulator.createAndShowUi();
-                    // Reset the simulator.
-                    simulator.handleReset();
-                } catch (Exception e) {
-                    e.printStackTrace();
-                }
-            }
-        });
-    }
-
     /**
      * The configuration has changed. Re-load.
      *
@@ -423,6 +392,28 @@ public class Simulator implements Observer {
         }
     }
 
+    /**
+     * Main entry point to the simulator. Creates a simulator and shows the main
+     * window.
+     *
+     * @param args
+     */
+    public static void main(String args[]) {
+        SwingUtilities.invokeLater(new Runnable() {
+            public void run() {
+                try {
+                    // Create the main UI window
+                    Simulator simulator = new Simulator();
+                    simulator.createAndShowUi();
+                    // Reset the simulator.
+                    simulator.handleReset();
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+            }
+        });
+    }
+
     /**
      * The main run thread.
      */
@@ -464,13 +455,15 @@ public class Simulator implements Observer {
 
             SwingUtilities.invokeLater(new Runnable() {
                 public void run() {
-                    console.stopListening();
-                    // Allow step while the simulator is stopped
-                    stepButton.setEnabled(true);
-                    menuBar.simulatorDidStop();
-                    runStopButton.setText("Run");
-                    // Now update the state
                     statusPane.updateState(cpu);
+                    runStopButton.setText("Run");
+                    stepButton.setEnabled(true);
+                    if (traceLog.isVisible()) {
+                        traceLog.refresh();
+                    }
+                    menuBar.simulatorDidStop();
+                    traceLog.simulatorDidStop();
+                    // TODO: Update memory window, if frame is visible.
                 }
             });
 

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

@@ -14,8 +14,8 @@ package com.loomcom.symon.util;
  * 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 part with <code>Integer.toHexString</code>,
+ * with <code>HexUtil</code> takes only 160ms. This is on par with <code>Integer.toHexString</code>,
- * but also allows the desired padding.
+ * but also gives the desired padding.
  *
  */
 public class HexUtil {

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

@@ -33,4 +33,10 @@ public class HexUtilTest extends TestCase {
         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));
+        }
+    }
 }