353 lines
9.0 KiB
JavaScript
353 lines
9.0 KiB
JavaScript
const { num2hex } = require('./logging.js');
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module.exports = class CPU {
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/**
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* @arg {number} initialIP
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**/
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constructor(initialIP, cycleLimit) {
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this.running = false;
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this.IP = initialIP;
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this.acc = 0;
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this.flags = {'C': false, 'Z': false, 'N': false, 'O': false};
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this.flagNums = {0: 'C', 1: 'Z', 2: 'N', 3: 'O'};
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this.instruction = { opcode: null, operand: null };
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this.memory = null;
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this._cycleLimit = cycleLimit;
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this.dbg = {
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sourceInfo: null,
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currentMnemonic: null,
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previousIP: initialIP,
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cycleCounter: 0,
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}
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}
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/** Public interface **/
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/**
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* @param {Uint8Array} machineCode
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**/
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loadMemory(machineCode) {
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this.memory = new Uint8Array(256);
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this.memory.set(machineCode, 0);
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}
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peek() { return; } // TODO - implement Peek
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poke() { return; } // TODO - implement Poke
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/** @param {Array} info **/ // TODO - document type for 'sourceInfo'
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loadSourceInfo(info) {
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this.dbg.sourceInfo = info;
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}
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/** Set CPU state to "state.running" **/
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start() {
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this.running = true;
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}
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/** Execute the next instruction in memory **/
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step() {
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this._cycleStartCallbacks.forEach((fn) => fn());
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if (this.IP >= this.memory.length) {
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console.error('HALTING - IP greater than memory size'); // FIXME - halting the CPU should throw an error instead
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this.running = false;
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} else {
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this.instruction.opcode = this.memory[this.IP];
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this.instruction.operand = this.memory[this.IP+1];
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let mnem = this._nums2mnems[this.instruction.opcode];
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let op = this._ops[mnem];
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if (typeof op === 'undefined') { this._failInvalidOpcode(); }
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op(this.instruction.operand);
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this.dbg.cycleCounter += 1;
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}
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// Temporary limit as a lazy way to halt infinite loops
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if ((this._cycleLimit > 0) && this.dbg.cycleCounter >= this._cycleLimit) {
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console.warn(' HALTING - reached cycle limit'); // FIXME - throw error instead
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this.running = false;
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}
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this._cycleEndCallbacks.forEach((fn) => fn());
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if (!this.running) process.exit();
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}
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/** Private methods **/
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_incrementIP(offset) {
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this.dbg.previousIP = this.IP;
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this.IP = this.IP + offset;
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}
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_setIP(address) {
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this.dbg.previousIP = this.IP;
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this.IP = address;
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}
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_updateFlagZero() {
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this.flags.Z = this.acc === 0;
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}
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_updateFlagNegative() {
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if (this.acc & 128)
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{ this.flags.N = true; }
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else
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{ this.flags.N = false; }
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}
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/** Hooks **/
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/** @type Array<Function> **/
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_cycleStartCallbacks = [];
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/** @type Array<Function> **/
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_cycleEndCallbacks = [];
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/** @param {function} fn **/
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onCycleStart(fn) { this._cycleStartCallbacks.push(fn) };
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/** @param {function} fn **/
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onCycleEnd(fn) { this._cycleEndCallbacks.push(fn) };
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_ops = {
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end: () => {
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this.dbg.currentMnemonic = 'END';
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this.running = false;
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this._incrementIP(2);
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},
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store_lit: (lit) => {
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this.dbg.currentMnemonic = 'STO lit';
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this.memory[lit] = this.acc;
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this._incrementIP(2);
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},
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store_addr: (addr) => {
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this.dbg.currentMnemonic = `STO addr; @addr: ${num2hex(this.memory[addr])}`;
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this.memory[this.memory[addr]] = this.acc;
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this._incrementIP(2);
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},
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load_lit: (lit) => {
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this.dbg.currentMnemonic = 'LDA lit';
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this.acc = lit;
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this._updateFlagNegative();
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this._updateFlagZero();
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this._incrementIP(2);
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},
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load_addr: (addr) => {
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this.dbg.currentMnemonic = `LDA addr; @ addr: ${num2hex(this.memory[addr])}`;
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this.acc = this.memory[addr];
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this._updateFlagNegative();
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this._updateFlagZero();
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this._incrementIP(2);
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},
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add_lit: (lit) => {
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this.dbg.currentMnemonic = 'ADD lit';
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// Calculate sum
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let sum = this.acc + lit;
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if (sum > 255) {
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this.flags.C = true;
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sum = (sum % 255) - 1;
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} else {
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this.flags.C = false;
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}
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// Calculate overflow flag status
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let bitSixCarry = 0;
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if ((this.acc & 64) && (lit & 64)) { bitSixCarry = 1; }
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// let overflow = bitSixCarry ^ (this.flags & 8);
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// FIXME - re-implement overflow
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// I'm on a plane and can't remember how this works
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let overflow = 0;
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if (overflow) {
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this.flags.O = true;
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} else {
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this.flags.O = false;
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}
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this.acc = sum;
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this._updateFlagNegative();
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this._updateFlagZero();
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this._incrementIP(2);
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},
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add_addr: (addr) => {
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this.dbg.currentMnemonic = 'ADD addr';
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// Calculate sum
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let sum = this.acc + this.memory[addr];
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if (sum > 255) {
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this.flags.C = true;
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sum = (sum % 255) - 1;
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} else {
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this.flags.C = false;
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}
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// Calculate overflow flag status
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let bitSixCarry = 0;
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if ((this.acc & 64) && (addr & 64)) { bitSixCarry = 1; }
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// let overflow = bitSixCarry ^ (this.flags & 8);
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// FIXME - re-implement overflow
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// I'm on a plane and can't remember how this works
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let overflow = 0;
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if (overflow) {
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this.flags.O = true;
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} else {
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this.flags.O = false;
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}
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this.acc = sum;
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this._updateFlagNegative();
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this._updateFlagZero();
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this._incrementIP(2);
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},
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sub_lit: (lit) => {
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this.dbg.currentMnemonic = 'SUB lit';
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// Calculate sum
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let sum = this.acc - lit;
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if (sum < 0) {
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this.flags.C = true;
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sum = sum + 256;
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} else {
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this.flags.C = false;
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}
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// Calculate overflow flag status
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let bitSixCarry = 0;
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if ((this.acc & 64) && (lit & 64)) { bitSixCarry = 1; }
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// let overflow = bitSixCarry ^ (this.flags & 8);
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// FIXME - re-implement overflow
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// I'm on a plane and can't remember how this works
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let overflow = 0;
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if (overflow) {
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this.flags.O = true;
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} else {
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this.flags.O = false;
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}
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this.acc = sum;
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this._updateFlagNegative();
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this._updateFlagZero();
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this._incrementIP(2);
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},
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sub_addr: (addr) => {
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this.dbg.currentMnemonic = 'SUB addr';
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// Calculate sum
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let sum = this.acc - this.memory[addr];
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if (sum < 0) {
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this.flags.C = true;
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sum = sum + 256;
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} else {
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this.flags.C = false;
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}
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// Calculate overflow flag status
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let bitSixCarry = 0;
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if ((this.acc & 64) && (addr & 64)) { bitSixCarry = 1; }
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// let overflow = bitSixCarry ^ (this.flags & 8);
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// FIXME - re-implement overflow
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// I'm on a plane and can't remember how this works
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let overflow = 0;
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if (overflow) {
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this.flags.O = true;
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} else {
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this.flags.O = false;
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}
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this.acc = sum;
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this._updateFlagNegative();
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this._updateFlagZero();
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this._incrementIP(2);
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},
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hop_lit: (lit) => {
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this.dbg.currentMnemonic = `HOP lit; IP+2: ${this.memory[this.IP+2]}, IP+3: ${this.memory[this.IP+3]}`;
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if (this.acc === lit) {
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this._incrementIP(4);
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} else {
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this._incrementIP(2);
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}
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},
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hop_addr: (addr) => {
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this.dbg.currentMnemonic = 'HOP addr';
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if (this.acc === this.memory[addr]) {
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this._incrementIP(4);
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} else {
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this._incrementIP(2);
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}
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},
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jump_lit: (lit) => {
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this.dbg.currentMnemonic = 'JMP lit';
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this._setIP(lit);
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},
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jump_addr: (addr) => {
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this.dbg.currentMnemonic = 'JMP addr';
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this._setIP(this.memory[addr]);
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},
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flag_toggle: (flagNum) => {
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if (flagNum === null) {
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console.error('Invalid flag number');
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process.exit(); // FIXME -- throw error instead
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}
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const flagName = this.flagNums[flagNum];
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this.dbg.currentMnemonic = `FTG ${flagName}`;
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this.flags[flagName] = !this.flags[flagName];
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this._incrementIP(2);
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},
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flag_hop: (flagNum) => {
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if (flagNum === null) {
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console.error('Invalid flag number');
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process.exit();
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}
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const flagName = this.flagNums[flagNum];
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this.dbg.currentMnemonic =
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`FHP ${flagName}; IP+2: ${this.memory[this.IP+2]}, IP+3: ${this.memory[this.IP+3]}`;
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if (this.flags[this.flagNums[flagNum]]) {
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this._incrementIP(4);
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} else {
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this._incrementIP(2);
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}
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},
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no_op: () => {
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this.dbg.currentMnemonic = `NOP`;
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this._incrementIP(2);
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},
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}
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_nums2mnems = {
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0: "end",
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1: "store_lit",
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2: "store_addr",
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3: "load_lit",
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4: "load_addr",
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5: "add_lit",
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6: "add_addr",
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7: "sub_lit",
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8: "sub_addr",
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9: "hop_lit",
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10: "hop_addr",
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11: "jump_lit",
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12: "jump_addr",
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13: "flag_toggle",
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14: "flag_hop",
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15: "no_op",
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}
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_failInvalidOpcode() {
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let info = this.dbg.sourceInfo[this.dbg.previousIP];
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console.error();
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console.error(`Error: Invalid opcode`);
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console.error(` Executing $${num2hex(info.machine[0])} $${num2hex(info.machine[1])}`);
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console.error(` from line ${info.lineNumber}: ${info.source}`);
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process.exit();
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}
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}
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