nes-emu/apu/APU.js

A NES emulator

"use strict";

Object.defineProperty(exports, "__esModule", {
  value: true
});
exports.default = void 0;
var _registers = require("./registers");
var _channels = require("./channels");
var _frameClock = _interopRequireDefault(require("./frameClock"));
var _constants = require("../cpu/constants");
var _config = _interopRequireDefault(require("../config"));
var _constants2 = _interopRequireDefault(require("../constants"));
var _helpers = require("../helpers");
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
const STEPS_PER_SAMPLE = Math.floor(_constants2.default.FREQ_APU_HZ / _constants2.default.APU_SAMPLE_RATE);

/** The Audio Processing Unit. It generates audio samples. */
class APU {
  constructor() {
    _helpers.WithContext.apply(this);
    this.sampleCounter = 0;
    this.frameClockCounter = 0;
    this.sample = 0;
    this.frameIRQFlag = false;
    this.registers = null;
    this.channels = {
      pulses: [new _channels.PulseChannel(0, "enablePulse1"), new _channels.PulseChannel(1, "enablePulse2")],
      triangle: new _channels.TriangleChannel(),
      noise: new _channels.NoiseChannel(),
      dmc: new _channels.DMCChannel()
    };
    this._onQuarter = this._onQuarter.bind(this);
    this._onHalf = this._onHalf.bind(this);
    this._onEnd = this._onEnd.bind(this);
  }

  /** When a context is loaded. */
  onLoad(context) {
    this.registers = new _registers.APURegisterSegment(context);
    this.channels.pulses[0].loadContext(context);
    this.channels.pulses[1].loadContext(context);
    this.channels.triangle.loadContext(context);
    this.channels.noise.loadContext(context);
    this.channels.dmc.loadContext(context);
    this._reset();
  }

  /**
   * Executes the next step (1 step = 1 APU cycle).
   * Returns an interrupt or null.
   * It calls `onSample` when it generates a new sample.
   */
  step(onSample) {
    let irq = null;
    const onIRQ = type => {
      if (type === "frame") {
        if (!this.registers.apuFrameCounter.interruptInhibitFlag) {
          this.frameIRQFlag = true;
          irq = _constants.interrupts.IRQ;
        }
      } else irq = _constants.interrupts.IRQ;
    };
    this._onNewCycle(onIRQ);
    this._incrementCounters();
    if (this.sampleCounter === 0) onSample(this.sample);
    return irq;
  }

  /** Returns a snapshot of the current state. */
  getSaveState() {
    return {
      sampleCounter: this.sampleCounter,
      frameClockCounter: this.frameClockCounter,
      sample: this.sample,
      frameIRQFlag: this.frameIRQFlag,
      pulse1: this.channels.pulses[0].getSaveState(),
      pulse2: this.channels.pulses[1].getSaveState(),
      triangle: this.channels.triangle.getSaveState(),
      noise: this.channels.noise.getSaveState(),
      dmc: this.channels.dmc.getSaveState()
    };
  }

  /** Restores state from a snapshot. */
  setSaveState(saveState) {
    this.sampleCounter = saveState.sampleCounter;
    this.frameClockCounter = saveState.frameClockCounter;
    this.sample = saveState.sample;
    this.frameIRQFlag = saveState.frameIRQFlag;
    this.channels.pulses[0].setSaveState(saveState.pulse1);
    this.channels.pulses[1].setSaveState(saveState.pulse2);
    this.channels.triangle.setSaveState(saveState.triangle);
    this.channels.noise.setSaveState(saveState.noise);
    this.channels.dmc.setSaveState(saveState.dmc);
  }
  _onNewCycle(onIRQ) {
    this.channels.pulses[0].cycle();
    this.channels.pulses[1].cycle();
    _frameClock.default.measure(this.frameClockCounter, this.registers.apuFrameCounter.use5StepSequencer, onIRQ, this._onQuarter, this._onHalf, this._onEnd);
    const isNewSample = this.sampleCounter + 1 === STEPS_PER_SAMPLE;
    const pulse1 = this.channels.pulses[0].sample(isNewSample); // 0 ~ 15
    const pulse2 = this.channels.pulses[1].sample(isNewSample); // 0 ~ 15
    const triangle = this.channels.triangle.sample(isNewSample); // 0 ~ 15
    const noise = this.channels.noise.sample(); // 0 ~ 15
    const dmc = this.channels.dmc.sample(onIRQ); // 0 ~ 127

    // (APU mixer from nesdev)
    const pulseOut = 0.00752 * (pulse1 + pulse2);
    const tndOut = 0.00851 * triangle + 0.00494 * noise + 0.00335 * dmc;
    this.sample = _config.default.BASE_VOLUME * (pulseOut + tndOut);
  }
  _onQuarter() {
    // (quarter frame "beats" adjust the volume envelope and triangle's linear length counter)

    this.channels.pulses[0].quarterBeat();
    this.channels.pulses[1].quarterBeat();
    this.channels.triangle.quarterBeat();
    this.channels.noise.quarterBeat();
  }
  _onHalf() {
    // (half frame "beats" adjust the note length and frequency sweepers)

    this.channels.pulses[0].halfBeat();
    this.channels.pulses[1].halfBeat();
    this.channels.triangle.halfBeat();
    this.channels.noise.halfBeat();
  }
  _onEnd() {
    this.frameClockCounter = 0;
  }
  _incrementCounters() {
    this.sampleCounter++;
    this.frameClockCounter++;
    if (this.sampleCounter === STEPS_PER_SAMPLE) this.sampleCounter = 0;
  }
  _reset() {
    this.sampleCounter = 0;
    this.frameClockCounter = 0;
    this.sample = 0;
    this.frameIRQFlag = false;
  }
}
exports.default = APU;