CPU bug fixes and Simulator enhancements.
Bug Fixes: - Fixed several bugs in the CPU that caused processor status flags to be set incorrectly. Instructions affected were: STA, STX, STY, CMP, CPX, CPY, BIT. - Made some internal-use-only methods on the CPU class private. - Fixed incorrect disassembly of (Indirect,X) and (Indirect),Y instructions. Although this didn't affect behavior, it certainly caused me some confusion in debugging. - Added missing "BCS" instruction to instruction table. Enhancements: - Now includes a full version of Lee Davison's Enhanced 6502 BASIC bundled as source code and a ROM image. Get that REAL COMPUTER EXPERIENCE!(tm) - If a file named "rom.bin" exists in the same directory where the simulator is executed, it will be loaded at addresses $d000-$ffff. - Gave the CPU an idle loop to make simulated timing a little more realistic (but this is still an area needing major improvement) - Changed the CPU's toString() method to give better debugging output. - Added a small typeahead buffer to the Console. - Better exception messaging. Misc: - Bumped version to 0.5, updated README.
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Seth Morabito committed
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@@ -2,6 +2,7 @@ package com.loomcom.symon;
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import com.loomcom.symon.devices.Acia;
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import com.loomcom.symon.devices.Memory;
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import com.loomcom.symon.exceptions.FifoUnderrunException;
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import com.loomcom.symon.exceptions.MemoryAccessException;
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import com.loomcom.symon.exceptions.MemoryRangeException;
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import com.loomcom.symon.exceptions.SymonException;
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@@ -14,7 +15,6 @@ import java.awt.event.ActionEvent;
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import java.awt.event.ActionListener;
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import java.awt.event.KeyEvent;
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import java.io.*;
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import java.lang.reflect.InvocationTargetException;
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import java.util.Observable;
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import java.util.Observer;
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import java.util.logging.Level;
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@@ -27,16 +27,16 @@ public class Simulator implements ActionListener, Observer {
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private static final int BUS_BOTTOM = 0x0000;
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private static final int BUS_TOP = 0xffff;
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// 32K of RAM
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private static final int MEMORY_BASE = 0x0000;
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private static final int MEMORY_SIZE = 0xc000; // 48 KB
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private static final int MEMORY_SIZE = 0xC000;
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private static final int ROM_BASE = 0xe000;
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private static final int ROM_SIZE = 0x2000; // 8 KB
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// IO area at $D000
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private static final int ACIA_BASE = 0xC000;
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private static final int ACIA_BASE = 0xc000;
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// The delay in microseconds between steps.
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private static final int DELAY_BETWEEN_STEPS_NS = 1000;
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// 8KB ROM at E000-FFFF
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private static final int ROM_BASE = 0xD000;
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private static final int ROM_SIZE = 0x3000;
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// Since it is very expensive to update the UI with Swing's Event Dispatch Thread, we can't afford
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// to refresh the view on every simulated clock cycle. Instead, we will only refresh the view after this
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@@ -84,18 +84,26 @@ public class Simulator implements ActionListener, Observer {
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private JFileChooser fileChooser;
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private PreferencesDialog preferences;
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public Simulator() throws MemoryRangeException {
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public Simulator() throws MemoryRangeException, IOException {
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this.acia = new Acia(ACIA_BASE);
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this.bus = new Bus(BUS_BOTTOM, BUS_TOP);
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this.cpu = new Cpu();
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this.ram = new Memory(MEMORY_BASE, MEMORY_SIZE, false);
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// TODO: Load this ROM from a file, of course!
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this.rom = new Memory(ROM_BASE, ROM_SIZE, false);
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// TODO: Make this configurable, of course.
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File romImage = new File("rom.bin");
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if (romImage.canRead()) {
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logger.info("Loading ROM image from file " + romImage);
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this.rom = Memory.makeROM(ROM_BASE, ROM_SIZE, romImage);
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} else {
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logger.info("No ROM file 'rom.bin' found. ROM image will be empty R/W memory.");
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// Just make it a normal RAM image.
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this.rom = Memory.makeRAM(ROM_BASE, ROM_SIZE);
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}
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bus.addCpu(cpu);
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bus.addDevice(acia);
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bus.addDevice(ram);
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bus.addDevice(acia);
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bus.addDevice(rom);
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}
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@@ -212,7 +220,7 @@ public class Simulator implements ActionListener, Observer {
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*/
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public void actionPerformed(ActionEvent actionEvent) {
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if (actionEvent.getSource() == resetButton) {
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handleReset();
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coldReset();
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} else if (actionEvent.getSource() == stepButton) {
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handleStep();
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} else if (actionEvent.getSource() == runStopButton) {
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@@ -274,7 +282,7 @@ public class Simulator implements ActionListener, Observer {
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}
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}
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private void handleReset() {
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private void coldReset() {
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if (runLoop != null && runLoop.isRunning()) {
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runLoop.requestStop();
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runLoop.interrupt();
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@@ -282,7 +290,7 @@ public class Simulator implements ActionListener, Observer {
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}
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try {
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logger.log(Level.INFO, "Reset requested. Resetting CPU and clearing memory.");
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logger.log(Level.INFO, "Cold reset requested. Resetting CPU and clearing memory.");
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// Reset and clear memory
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cpu.reset();
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ram.fill(0x00);
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@@ -307,6 +315,7 @@ public class Simulator implements ActionListener, Observer {
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private void handleStep() {
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try {
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step();
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// The simulator is lazy about updating the UI for performance reasons, so always request an
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// immediate update after stepping manually.
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SwingUtilities.invokeLater(new Runnable() {
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@@ -337,8 +346,6 @@ public class Simulator implements ActionListener, Observer {
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*/
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private void step() throws MemoryAccessException {
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delayLoop();
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cpu.step();
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// Read from the ACIA and immediately update the console if there's
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@@ -351,8 +358,12 @@ public class Simulator implements ActionListener, Observer {
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// If a key has been pressed, fill the ACIA.
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// TODO: Interrupt handling.
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if (console.hasInput()) {
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acia.rxWrite((int)console.readInputChar());
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try {
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if (console.hasInput()) {
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acia.rxWrite((int)console.readInputChar());
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}
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} catch (FifoUnderrunException ex) {
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logger.severe("Console type-ahead buffer underrun!");
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}
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// This is a very expensive update, and we're doing it without
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@@ -374,8 +385,6 @@ public class Simulator implements ActionListener, Observer {
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* Load a program into memory at the simulatorDidStart address.
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*/
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private void loadProgram(byte[] program, int startAddress) throws MemoryAccessException {
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cpu.setResetVector(startAddress);
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int addr = startAddress, i;
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for (i = 0; i < program.length; i++) {
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bus.write(addr++, program[i] & 0xff);
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@@ -388,6 +397,9 @@ public class Simulator implements ActionListener, Observer {
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// Reset (but don't clear memory, naturally)
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cpu.reset();
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// Reset the stack program counter
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cpu.setProgramCounter(preferences.getProgramStartAddress());
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// Immediately update the UI.
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SwingUtilities.invokeLater(new Runnable() {
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public void run() {
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@@ -405,8 +417,8 @@ public class Simulator implements ActionListener, Observer {
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Simulator simulator = new Simulator();
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simulator.createAndShowUi();
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// Reset the simulator.
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simulator.handleReset();
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} catch (MemoryRangeException e) {
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simulator.coldReset();
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} catch (Exception e) {
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e.printStackTrace();
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}
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}
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@@ -433,15 +445,6 @@ public class Simulator implements ActionListener, Observer {
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}
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}
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/*
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* Perform a busy-loop for DELAY_BETWEEN_STEPS_NS nanoseconds
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*/
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private void delayLoop() {
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long startTime = System.nanoTime();
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long stopTime = startTime + DELAY_BETWEEN_STEPS_NS;
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// Busy loop
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while (System.nanoTime() < stopTime) { ; }
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}
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/**
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* The main run thread.
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@@ -496,4 +499,4 @@ public class Simulator implements ActionListener, Observer {
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isRunning = false;
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}
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}
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}
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}
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