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Read the new DMA source address after the interrupt that triggers a new DMA, not before

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This commit is contained in:
Julien Bernard 2026-02-17 19:36:30 +01:00
parent 9323074ada
commit 96bba125e1
1 changed files with 41 additions and 15 deletions
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56
Source/Core/Core/HW/DSP.cpp
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@ -424,30 +424,56 @@ void DSPManager::UpdateDSPSlice(int cycles)
void DSPManager::UpdateAudioDMA()
{
static short zero_samples[8 * 2] = {0};
bool dma_samples_transmitted = false;
// Proper modelling of the hardware reality would mark the DMA as disabled when the DMA
// finishes (enabled and disabled really mean started and stopped, given the Nintendo SDK
// "enables" the DMA every 5ms), and then we would handle "a new DMA starting while none
// is in progress" accordingly in the MMIO handler.
//
// However, currently the MMIO handler only runs for the very first DMA start, and
// schedules an interrupt immediately in the future (200 cycles ~ 0.4ms). In steady state
// that would be wrong, it must be 5ms after previous interrupt (for Nintendo SDK games).
// But because it seems to be carefully chosen as per comment above, we just leave it be
// to not break compatibilities, and handle the "DMA finishes" logic in the "update the
// DMA" routine.
//
// Note that (for GC games using the Nintendo SDK at least), the AID interrupt is the one
// that triggers a new DMA. So, we defer reading the address/block number, the logic is:
// 'we just finished an ongoing DMA' -> trigger an AID INT = another DMA
// 'there was no ongoing DMA (blocks count already 0), meaning we triggered an AID INT
// just before and should now have a new DMA)' -> loads the new source address now
//
// This is not a race condition, the UpdateAudioDMA function is triggered by CPU ticks
// and the next call is thus guaranteed to happen after the AID interrupt handler
if (m_audio_dma.AudioDMAControl.Enable)
{
// Read audio at g_audioDMA.current_source_address in RAM and push onto an
// external audio fifo in the emulator, to be mixed with the disc
// streaming output.
auto& memory = m_system.GetMemory();
void* address = memory.GetPointerForRange(m_audio_dma.current_source_address, 32);
AudioCommon::SendAIBuffer(m_system, static_cast<short*>(address), 8);
if (m_audio_dma.remaining_blocks_count != 0)
{
m_audio_dma.remaining_blocks_count--;
m_audio_dma.current_source_address += 32;
}
if (m_audio_dma.remaining_blocks_count == 0)
{
m_audio_dma.current_source_address = m_audio_dma.SourceAddress;
m_audio_dma.remaining_blocks_count = m_audio_dma.AudioDMAControl.NumBlocks;
}
GenerateDSPInterrupt(DSP::INT_AID, 0);
if (m_audio_dma.remaining_blocks_count != 0)
{
// Read audio at g_audioDMA.current_source_address in RAM and push onto an
// external audio fifo in the emulator, to be mixed with the disc
// streaming output.
auto& memory = m_system.GetMemory();
void* address = memory.GetPointerForRange(m_audio_dma.current_source_address, 32);
AudioCommon::SendAIBuffer(m_system, static_cast<short*>(address), 8);
dma_samples_transmitted = true;
m_audio_dma.remaining_blocks_count--;
m_audio_dma.current_source_address += 32;
if (m_audio_dma.remaining_blocks_count == 0)
GenerateDSPInterrupt(DSP::INT_AID, 0);
}
}
else
if (!dma_samples_transmitted)
{
AudioCommon::SendAIBuffer(m_system, &zero_samples[0], 8);
}