broken-neees/apu/NoiseChannel.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 _LengthCounter = _interopRequireDefault(require("./LengthCounter"));
var _VolumeEnvelope = _interopRequireDefault(require("./VolumeEnvelope"));
var _noisePeriods = _interopRequireDefault(require("../lib/apu/noisePeriods"));
var _byte = _interopRequireDefault(require("../lib/byte"));
function _interopRequireDefault(e) { return e && e.__esModule ? e : { default: e }; }
class NoiseChannel {
  constructor(apu) {
    this.apu = apu;
    this.registers = this.apu.registers.noise;
    this.lengthCounter = new _LengthCounter.default();
    this.volumeEnvelope = new _VolumeEnvelope.default();
    this.shift = 0b1; // (the shift register is 15 bits wide)
    this.dividerCount = 0;
  }
  sample() {
    if (!this.isEnabled() || !this.lengthCounter.isActive() || this.isMuted()) return 0;
    return this.registers.control.constantVolume ? this.registers.control.volumeOrEnvelopePeriod : this.volumeEnvelope.volume;
  }
  step() {
    this.dividerCount++;
    if (this.dividerCount >= _noisePeriods.default[this.registers.form.periodId]) this.dividerCount = 0;else return;
    const bitPosition = this.registers.form.mode ? 6 : 1;
    const bit = _byte.default.getBit(this.shift, bitPosition);
    const feedback = _byte.default.getBit(this.shift, 0) ^ bit;
    this.shift = this.shift >> 1 | feedback << 14;
  }
  quarterFrame() {
    this.volumeEnvelope.clock(this.registers.control.volumeOrEnvelopePeriod, this.registers.control.envelopeLoopOrLengthCounterHalt);
  }
  halfFrame() {
    this.lengthCounter.clock(this.isEnabled(), this.registers.control.envelopeLoopOrLengthCounterHalt);
  }
  isEnabled() {
    return !!this.apu.registers.apuControl.enableNoise;
  }
  isMuted() {
    return !_byte.default.getBit(this.shift, 0);
  }
}
exports.default = NoiseChannel;