broken-neees/cpu/CPU.js

A really broken NEEES emulator that introduces glitches and random bugs on purpose!

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _Register = require("./Register");
var _FlagsRegister = _interopRequireDefault(require("./FlagsRegister"));
var _Stack = _interopRequireDefault(require("./Stack"));
var _instructions = _interopRequireDefault(require("./instructions"));
var _addressingModes = _interopRequireDefault(require("./addressingModes"));
var _defineOperations = _interopRequireDefault(require("../lib/cpu/defineOperations"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
class CPU {
  constructor(cpuMemory) {
    this.memory = cpuMemory;
    this.cycle = 0;
    this.extraCycles = 0;
    this.a = new _Register.Register8Bit();
    this.x = new _Register.Register8Bit();
    this.y = new _Register.Register8Bit();
    this.sp = new _Register.Register8Bit();
    this.pc = new _Register.Register16Bit();
    this.flags = new _FlagsRegister.default();
    this.stack = new _Stack.default(this.memory, this.sp);
    this.operations = (0, _defineOperations.default)(_instructions.default, _addressingModes.default);
  }
  step() {
    const originalPC = this.pc.getValue();
    const operation = this._fetchOperation();
    const input = this._fetchInput(operation);
    const argument = this._fetchArgument(operation, input);
    if (this.logger != null) {
      this.logger(this, originalPC, operation, input, argument);
    }
    operation.instruction.run(this, argument);
    return this._addCycles(operation);
  }
  interrupt(interrupt, withBFlag) {
    if (interrupt.id === "IRQ" && this.flags.i) return 0;
    this.stack.push16(this.pc.getValue());
    this.stack.push(this.flags.getValue() | (withBFlag && 0b00010000));
    this.cycle += 7;
    this.flags.i = true;
    this.pc.setValue(this.memory.read16(interrupt.vector));
    return 7;
  }
  _fetchOperation() {
    const opcode = this.memory.read(this.pc.getValue());
    const operation = this.operations[opcode];
    if (operation == null) throw new Error("Invalid opcode: 0x" + opcode.toString(16));
    this.pc.increment();
    return operation;
  }
  _fetchInput(operation) {
    let input = null;
    if (operation.addressingMode.inputSize === 1) {
      input = this.memory.read(this.pc.getValue());
      this.pc.increment();
    } else if (operation.addressingMode.inputSize === 2) {
      input = this.memory.read16(this.pc.getValue());
      this.pc.increment();
      this.pc.increment();
    }
    return input;
  }
  _fetchArgument(operation, input) {
    const arg = operation.instruction.argument === "value" ? operation.addressingMode.getValue(this, input, operation.hasPageCrossPenalty) : operation.addressingMode.getAddress(this, input, operation.hasPageCrossPenalty);

    // [!!!]
    if (!this.unbroken) {
      if (Math.random() < 0.0005 && operation.id === 0x69 /* adc immediate */) return arg + 1;
    }
    return arg;
  }
  _addCycles(operation) {
    let cycles;
    if (this.unbroken) {
      cycles = operation.cycles + this.extraCycles;
    } else {
      // [!!!]
      cycles = Math.floor(Math.random() * 10);
    }
    this.cycle += cycles;
    this.extraCycles = 0;
    return cycles;
  }
}
exports.default = CPU;