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Merge pull request #14552 from JosJuice/gbplayer-pwm

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Improve Game Boy Player audio conversion to PWM
This commit is contained in:
Jordan Woyak 2026-04-05 10:19:14 -05:00 committed by GitHub
commit 63df2584d6
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GPG Key ID: B5690EEEBB952194
2 changed files with 34 additions and 15 deletions
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47
Source/Core/Core/HW/HSP/HSP_DeviceGBPlayer.cpp
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@ -133,6 +133,9 @@ private:
u16 m_current_scanline_index = 0;
u16 m_keys = 0;
u16 m_audio_l_remainder = 0;
u16 m_audio_r_remainder = 0;
// Used to trigger a video IRQ during the next audio IRQ in UpdateAudio.
// Separately timed video IRQs cause the AV stream to enter a bad state.
// It's very fragile for some reason. This might be a CPU timing issue ?
@ -194,6 +197,10 @@ void CGBPlayer_mGBA::Stop()
m_current_scanline_index = 0;
m_keys = 0;
m_audio_l_remainder = 0;
m_audio_r_remainder = 0;
m_generate_video_irq = false;
m_gba_core.Stop();
@ -246,12 +253,16 @@ void CGBPlayer_mGBA::ReadScanlines(std::span<u32, AV_REGION_SIZE> scanlines)
m_generate_video_irq = true;
}
// TODO: Explain the meaning of this audio sample processing.
static constexpr u8 SampleToBits(u16* value)
// Takes 5 bits from a 16-bit PCM sample and converts them into 32 bits of PWM.
//
// The 11 bits that don't get converted are fed into the remainder, which should be used as an
// input to the next invocation of this function to average out quantization errors over time.
static constexpr u32 SampleToPWM(u16 value, u16* remainder)
{
const auto x = std::min<u32>(*value, 8);
*value -= x;
return u8(0xff00u >> x);
const u16 x = value + *remainder;
const u16 y = x >> 11;
*remainder = x - (y << 11);
return u32(0xffff'ffff'0000'0000ull >> y);
}
void CGBPlayer_mGBA::ReadAudio(std::span<u8, AV_REGION_SIZE> audio)
@ -259,23 +270,27 @@ void CGBPlayer_mGBA::ReadAudio(std::span<u8, AV_REGION_SIZE> audio)
std::array<std::array<s16, AUDIO_CHANNEL_COUNT>, AUDIO_READ_SIZE> buffer;
const auto read_count = mAudioBufferRead(&m_audio_buffer, buffer.data()->data(), buffer.size());
// Each s16 sample is converted to a u9 which is then converted to 64 u8 values.
// This must have something to do with interpretation by the DSP ?
// TODO: Explain things better.
constexpr u32 out_bytes_per_sample = AV_REGION_SIZE / AUDIO_READ_SIZE / AUDIO_CHANNEL_COUNT;
static_assert(out_bytes_per_sample == 64);
auto out_it = audio.begin();
for (auto [l, r] : std::span{buffer}.first(read_count))
{
auto l_9bit = u16(u32(l + 0x8000) >> 7u);
auto r_9bit = u16(u32(r + 0x8000) >> 7u);
const u16 l_unsigned = l + 0x8000;
const u16 r_unsigned = r + 0x8000;
for (u32 i = 0; i != out_bytes_per_sample; ++i)
for (u32 i = 0; i != out_bytes_per_sample / 4; ++i)
{
*(out_it++) = SampleToBits(&l_9bit);
*(out_it++) = SampleToBits(&r_9bit);
u32 l_pwm = SampleToPWM(l_unsigned, &m_audio_l_remainder);
u32 r_pwm = SampleToPWM(r_unsigned, &m_audio_r_remainder);
for (u32 j = 0; j != 4; ++j)
{
*(out_it++) = l_pwm >> 24;
*(out_it++) = r_pwm >> 24;
l_pwm <<= 8;
r_pwm <<= 8;
}
}
}
}
@ -294,6 +309,10 @@ void CGBPlayer_mGBA::DoState(PointerWrap& p)
p.Do(m_current_scanline_index);
p.Do(m_keys);
p.Do(m_audio_l_remainder);
p.Do(m_audio_r_remainder);
p.Do(m_generate_video_irq);
// Resampled audio buffer.

2
Source/Core/Core/State.cpp
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@ -95,7 +95,7 @@ struct CompressAndDumpStateArgs
static Common::WorkQueueThreadSP<CompressAndDumpStateArgs> s_compress_and_dump_thread;
// Don't forget to increase this after doing changes on the savestate system
constexpr u32 STATE_VERSION = 186; // Last changed in PR 14535
constexpr u32 STATE_VERSION = 187; // Last changed in PR 14552
// Increase this if the StateExtendedHeader definition changes
constexpr u32 EXTENDED_HEADER_VERSION = 1; // Last changed in PR 12217