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NES: Add MMC5 PCM IRQ #199

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NES: Add MMC5 PCM IRQ #199

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a2334dc
NES: Add MMC5 PCM IRQ
HeeminTV Jun 28, 2026
16875bc
NES: Serialize MMC5 PCM variable and randomize DAC value according to…
HeeminTV Jun 28, 2026
2e876f5
NES: Reformat MMC5 sources
HeeminTV Jun 28, 2026
61d4fd2
Merge branch 'nesdev-org:master' into mmc5_pcm_irq
HeeminTV Jul 10, 2026
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33 changes: 22 additions & 11 deletions Core/NES/Mappers/Audio/Mmc5Audio.h
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,8 @@ class Mmc5Square : public SquareChannel
}

public:
Mmc5Square(NesConsole* console) : SquareChannel(AudioChannel::MMC5, console, false)
Mmc5Square(NesConsole* console)
: SquareChannel(AudioChannel::MMC5, console, false)
{
_currentOutput = 0;
_isMmc5Square = true;
Expand Down Expand Up @@ -59,7 +60,8 @@ class Mmc5Audio : public ISerializable

bool _pcmReadMode = false;
bool _pcmIrqEnabled = false;
uint8_t _pcmOutput = 0;
bool _pcmIrqPending = false;
uint8_t _pcmOutput;

protected:
void Serialize(Serializer& s) override
Expand All @@ -70,6 +72,7 @@ class Mmc5Audio : public ISerializable
SV(_lastOutput);
SV(_pcmReadMode);
SV(_pcmIrqEnabled);
SV(_pcmIrqPending);
SV(_pcmOutput);
}

Expand Down Expand Up @@ -104,7 +107,8 @@ class Mmc5Audio : public ISerializable
_square2.ReloadLengthCounter();
}

Mmc5Audio(NesConsole* console) : _square1(console), _square2(console)
Mmc5Audio(NesConsole* console)
: _square1(console), _square2(console)
{
_console = console;
_apu = console->GetApu();
Expand All @@ -117,10 +121,15 @@ class Mmc5Audio : public ISerializable
}

__forceinline bool GetPcmReadMode() { return _pcmReadMode; }
__forceinline bool GetPcmIRQLine() { return _pcmIrqEnabled && _pcmIrqPending; }

void HandlePcmRead(uint16_t addr, uint8_t value)
//$5011 write
//+ "Write-by-read writes to this register in PCM read-mode."
void DacWrite(uint8_t value)
{
if((addr & 0xC000) == 0x8000 && value) {
if(value == 0) {
_pcmIrqPending = true;
} else {
_pcmOutput = value;
}
}
Expand All @@ -129,8 +138,12 @@ class Mmc5Audio : public ISerializable
{
switch(addr) {
case 0x5010:
//TODO: PCM IRQ
return 0;
if(_pcmIrqPending) {
_pcmIrqPending = false;
return 0x80;
} else {
return 0x00;
}

case 0x5015:
uint8_t status = 0;
Expand Down Expand Up @@ -160,16 +173,13 @@ class Mmc5Audio : public ISerializable
break;

case 0x5010:
//TODO: PCM IRQs
_pcmReadMode = (value & 0x01) == 0x01;
_pcmIrqEnabled = (value & 0x80) == 0x80;
break;

case 0x5011:
if(!_pcmReadMode) {
if(value != 0) {
_pcmOutput = value;
}
DacWrite(value);
}
break;

Expand Down Expand Up @@ -234,6 +244,7 @@ class Mmc5Audio : public ISerializable
entries.push_back(MapperStateEntry("$5010-$5011", "PCM"));
entries.push_back(MapperStateEntry("$5010.0", "PCM Read Mode", _pcmReadMode));
entries.push_back(MapperStateEntry("$5010.7", "PCM IRQ Enabled", _pcmIrqEnabled));
entries.push_back(MapperStateEntry("$5010.7", "PCM IRQ Pending", _pcmIrqPending));
entries.push_back(MapperStateEntry("$5011", "PCM Output", _pcmOutput, MapperStateValueType::Number8));
}
};
31 changes: 19 additions & 12 deletions Core/NES/Mappers/Nintendo/MMC5.h
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Original file line number Diff line number Diff line change
Expand Up @@ -354,6 +354,10 @@ class MMC5 : public BaseMapper, public IExtModeMapperDebug
WriteRegister(0x5117, 0xFF);

UpdateChrBanks(true);

//The same MMC5A chip, tested with repeated power cycles on different days of the week and different moon phases, etc,
//has been observed to power on with a DAC voltage equivalent to DAC value $EF or $FF.
_audio->DacWrite((GetPowerOnByte() & 0x01) ? 0xFF : 0xEF);
}

virtual ~MMC5()
Expand Down Expand Up @@ -439,11 +443,20 @@ class MMC5 : public BaseMapper, public IExtModeMapperDebug
}
}

void UpdateIrqState()
{
if((_irqEnabled && _irqPending) || _audio->GetPcmIRQLine()) {
_console->GetCpu()->SetIrqSource(IRQSource::External);
} else {
_console->GetCpu()->ClearIrqSource(IRQSource::External);
}
}

uint8_t ReadRam(uint16_t addr) override
{
uint8_t value = BaseMapper::InternalRead(addr);
if(_audio->GetPcmReadMode()) {
_audio->HandlePcmRead(addr, value);
if(_audio->GetPcmReadMode() && (addr & 0xC000) == 0x8000) {
_audio->DacWrite(value);
}
return value;
}
Expand All @@ -469,9 +482,7 @@ class MMC5 : public BaseMapper, public IExtModeMapperDebug
_scanlineCounter++;
if(_irqCounterTarget == _scanlineCounter) {
_irqPending = true;
if(_irqEnabled) {
_console->GetCpu()->SetIrqSource(IRQSource::External);
}
UpdateIrqState();
}
}
} else if(addr >= 0x2000 && addr <= 0x2FFF) {
Expand Down Expand Up @@ -641,11 +652,7 @@ class MMC5 : public BaseMapper, public IExtModeMapperDebug
case 0x5203: _irqCounterTarget = value; break;
case 0x5204:
_irqEnabled = (value & 0x80) == 0x80;
if(!_irqEnabled) {
_console->GetCpu()->ClearIrqSource(IRQSource::External);
} else if(_irqEnabled && _irqPending) {
_console->GetCpu()->SetIrqSource(IRQSource::External);
}
UpdateIrqState();
break;
case 0x5205: _multiplierValue1 = value; break;
case 0x5206: _multiplierValue2 = value; break;
Expand All @@ -666,7 +673,7 @@ class MMC5 : public BaseMapper, public IExtModeMapperDebug
case 0x5204: {
uint8_t value = (_ppuInFrame ? 0x40 : 0x00) | (_irqPending ? 0x80 : 0x00);
_irqPending = false;
_console->GetCpu()->ClearIrqSource(IRQSource::External);
UpdateIrqState();
return value;
}

Expand All @@ -680,7 +687,7 @@ class MMC5 : public BaseMapper, public IExtModeMapperDebug
_lastPpuReadAddr = 0;
_scanlineCounter = 0;
_irqPending = false;
_console->GetCpu()->ClearIrqSource(IRQSource::External);
UpdateIrqState();
return DebugReadRam(addr);
}

Expand Down
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