bsnes/higan/fc/apu/pulse.cpp

auto APU::Pulse::clockLength() -> void {
  if(envelope.loopMode == 0) {
    if(lengthCounter) lengthCounter--;
  }
}

auto APU::Pulse::clock() -> uint8 {
  if(!sweep.checkPeriod()) return 0;
  if(lengthCounter == 0) return 0;

  static const uint dutyTable[4][8] = {
    {0, 0, 0, 0, 0, 0, 0, 1},  //12.5%
    {0, 0, 0, 0, 0, 0, 1, 1},  //25.0%
    {0, 0, 0, 0, 1, 1, 1, 1},  //50.0%
    {1, 1, 1, 1, 1, 1, 0, 0},  //25.0% (negated)
  };
  uint8 result = dutyTable[duty][dutyCounter] ? envelope.volume() : 0;
  if(sweep.pulsePeriod < 0x008) result = 0;

  if(--periodCounter == 0) {
    periodCounter = (sweep.pulsePeriod + 1) * 2;
    dutyCounter--;
  }

  return result;
}

auto APU::Pulse::power() -> void {
  envelope.power();
  sweep.power();

  lengthCounter = 0;

  duty = 0;
  dutyCounter = 0;
  period = 0;
  periodCounter = 1;
}