minor fixes

* zero out all registers
* capture pids for each timers and use them for pause/reset

Author: chrisledet

index.js

@@ -6,7 +6,8 @@ const resumeSwitch = document.getElementById("resume");
 const uploader = document.getElementById("rom-uploader");
 const romSelector = document.getElementById("rom-selector");
 const stopSwitch = document.getElementById("stop");
-const keyButtons = document.getElementsByClassName("key")
+const keyButtons = document.getElementsByClassName("key");
+
 Array.from(keyButtons).forEach(b => {
   b.onclick = (e) => {
     const input = Number(e.target.dataset.input);

js/CPU.js

@@ -48,20 +48,18 @@ export default class CPU {
     ];
     this.awaitInput = false;
     this.currentInput = 0x0;
-    this.debugMode = false;
+    this.debugMode = true;
   }
 
   debug() {
     if (this.debugMode) {
-      console.log(arguments);
+      console.log(...arguments);
     }
   }
 
   loadRom(data) {
     this.debug("Loading ROM");
-
     this.reset();
-
     this.copyIntoMemory(0x0, this.font);
     this.copyIntoMemory(0x200, data);
   }
@@ -91,7 +89,7 @@ export default class CPU {
   }
 
   reset() {
-    for (let x = 0; x < 0xF; x++) {
+    for (let x = 0; x <= 0xF; x++) {
       this.v[x] = 0x0;
     }
 
@@ -141,7 +139,7 @@ export default class CPU {
       this.pc = nnn - 2; // -2 because pc is incremented after each
       break;
     case 0x3:
-      this.debug("EXEC: SKIP IF VX == NN", nn);
+      this.debug("EXEC: SKIP IF VX == NN", "x", x, "nn", nn, "v[x]", this.v[x]);
       if (this.v[x] == nn) {
         this.pc += 2;
       }
@@ -190,6 +188,11 @@ export default class CPU {
 
       case 0x3:
         // Sets VX to VX xor VY.
+        // Performs a bitwise exclusive OR on the values of Vx and Vy,
+        // then stores the result in Vx.
+        // An exclusive OR compares the corrseponding bits from two values,
+        // and if the bits are not both the same,
+        // then the corresponding bit in the result is set to 1. Otherwise, it is 0.
         if (this.v[x] == this.v[y]) {
           this.v[x] = 0x0;
         } else {
@@ -383,7 +386,6 @@ export default class CPU {
   /* private */
   copyIntoMemory(startAddress, data) {
     for (let x = 0; x < data.length; x++) {
-      this.debug("Loading ", data[x].toString(16), " in address " + (startAddress + x).toString(16));
       this.memory[startAddress + x] = data[x];
     }
   }

js/System.js

@@ -6,45 +6,51 @@ export default class System {
     const display = new Display(displaySource);
     const audio = audioSource ? new Audio(audioSource) : null;
 
+    this.cpu = new CPU(display, audio);
     this.clockRate = 300;
-    this._pid = null;
-    this._cpu = new CPU(display, audio);
+    this.stepPid = null;
+    this.timerPid = null;
   }
 
   boot(rom) {
     this.stop();
-
-    this._cpu.reset();
-    this._cpu.loadRom(rom);
-
+    this.cpu.loadRom(rom);
     this.start();
   }
 
   start() {
-    if (this._pid) { return; }
+    if (this.stepPid || this.timerPid) {
+      return;
+    }
 
-    this._pid = window.setInterval(() => {
-      this._cpu.step();
+    this.stepPid = window.setInterval(() => {
+      this.cpu.step();
     }, 1000/this.clockRate);
-    this._pid = window.setInterval(() => {
-      this._cpu.stepTimer();
+
+    this.timerPid = window.setInterval(() => {
+      this.cpu.stepTimer();
     }, 1000/60); // delay and sound timers run at fixed 60Hz
   }
 
   stop() {
-    if (!this._pid) { return; }
-
-    window.clearInterval(this._pid);
-    this._pid = null;
+    if (this.stepPid) {
+      window.clearInterval(this.stepPid);
+    }
+    if (this.timerPid) {
+       window.clearInterval(this.timerPid);
+    }
+
+    this.stepPid = null;
+    this.timerPid = null;
   }
 
   reset() {
     this.stop();
-    this._cpu.reset();
+    this.cpu.reset();
   }
 
   setInput(input) {
-    this._cpu.setInput(input);
+    this.cpu.setInput(input);
   }
 }