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https://github.com/libretro/Mesen.git
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88 lines
2.2 KiB
C++
88 lines
2.2 KiB
C++
#pragma once
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#include "stdafx.h"
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#include "../BlipBuffer/Blip_Buffer.h"
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#include "APU.h"
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#include "IMemoryHandler.h"
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#include "ApuEnvelope.h"
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class NoiseChannel : public ApuEnvelope
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{
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private:
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const vector<uint16_t> _noisePeriodLookupTableNtsc = { { 4, 8, 16, 32, 64, 96, 128, 160, 202, 254, 380, 508, 762, 1016, 2034, 4068 } };
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const vector<uint16_t> _noisePeriodLookupTablePal = { { 4, 8, 14, 30, 60, 88, 118, 148, 188, 236, 354, 472, 708, 944, 1890, 3778 } };
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//On power-up, the shift register is loaded with the value 1.
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uint16_t _shiftRegister = 1;
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bool _modeFlag = false;
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bool IsMuted()
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{
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//The mixer receives the current envelope volume except when Bit 0 of the shift register is set, or The length counter is zero
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return (_shiftRegister & 0x01) == 0x01;
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}
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protected:
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void Clock()
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{
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//Feedback is calculated as the exclusive-OR of bit 0 and one other bit: bit 6 if Mode flag is set, otherwise bit 1.
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uint16_t feedback = (_shiftRegister & 0x01) ^ ((_shiftRegister >> (_modeFlag ? 6 : 1)) & 0x01);
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_shiftRegister >>= 1;
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_shiftRegister |= (feedback << 14);
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if(IsMuted()) {
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AddOutput(0);
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} else {
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AddOutput(GetVolume());
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}
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}
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public:
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NoiseChannel(AudioChannel channel, Blip_Buffer* buffer) : ApuEnvelope(channel, buffer)
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{
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SetVolume(0.0741);
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}
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virtual void Reset(bool softReset)
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{
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ApuEnvelope::Reset(softReset);
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_shiftRegister = 1;
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_modeFlag = false;
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}
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virtual void StreamState(bool saving)
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{
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ApuEnvelope::StreamState(saving);
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Stream<uint16_t>(_shiftRegister);
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Stream<bool>(_modeFlag);
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}
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void GetMemoryRanges(MemoryRanges &ranges)
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{
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ranges.AddHandler(MemoryOperation::Write, 0x400C, 0x400F);
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}
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void WriteRAM(uint16_t addr, uint8_t value)
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{
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APU::StaticRun();
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switch(addr & 0x03) {
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case 0: //400C
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InitializeLengthCounter((value & 0x20) == 0x20);
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InitializeEnvelope(value);
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break;
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case 2: //400E
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_period = (GetNesModel() == NesModel::NTSC ? _noisePeriodLookupTableNtsc : _noisePeriodLookupTablePal)[value & 0x0F] - 1;
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_modeFlag = (value & 0x80) == 0x80;
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break;
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case 3: //400F
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LoadLengthCounter(value >> 3);
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//The envelope is also restarted.
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ResetEnvelope();
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break;
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}
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}
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}; |