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Refactor sound generation
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Previously, each console core used to sample the sound at 22050 Hz, and the
output was sent directly to SDL. However, this isn't very portable, as the
sample rate returned by SDL may not be 22050.

The new code generates samples at 32768 Hz in both the GB and GBA cores,
which is sent to an SDL AudioStream, which resamples it to whichever sample
rate is chosen by SDL as output sample rate.

This makes it a lot easier to record accurate WAVs from the emulator cores,
because the 32768 Hz audio is deterministic. The step that resamples it to
send it to the output may need to drop samples every now and then, but the
output of the cores is always the same.
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@AntonioND
AntonioND committed Dec 30, 2020
1 parent 8a2a668 commit 89403ec
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Showing 7 changed files with 179 additions and 232 deletions.
106 changes: 34 additions & 72 deletions source/gb_core/sound.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -26,6 +26,8 @@
#define GB_BUFFER_SIZE (16384)
#define GB_BUFFER_SAMPLES (GB_BUFFER_SIZE / 2)

#define GB_SAMPLE_RATE (32 * 1024)

extern _GB_CONTEXT_ GameBoy;

static const s8 GB_SquareWave[4][32] = {
Expand Down Expand Up @@ -165,11 +167,9 @@ typedef struct
u32 clocks;

u32 nextsample_clocks;
s16 buffer[GB_BUFFER_SIZE / 2];
u32 buffer_next_input_sample;
u32 buffer_next_output_sample;
int samples_left_to_input;
int samples_left_to_output;

s16 buffer[GB_SAMPLE_RATE];
u32 buffer_write_ptr;

// Some temporary variables to avoid doing the same calculations every time
// a sample is going to be generated:
Expand Down Expand Up @@ -216,42 +216,27 @@ void GB_SoundPowerOn(void)
Sound.Chn4.seed = 0xFF;
}

void GB_SoundCallback(void *buffer, long len)
// This function is supposed to return all the samples taken during a frame. If
// the destination buffer isn't big enough, it will clear the source buffer
// anyway, to prepare it for next frame.
size_t GB_SoundGetSamplesFrame(void *buffer, size_t buffer_size)
{
if (output_enabled == 0)
{
memset(buffer, 0, len);
return;
}
size_t available_size = Sound.buffer_write_ptr * 2;

//Should print: (GB_BUFFER_SAMPLES / 3 * 2) - (GB_BUFFER_SAMPLES / 3)
//Debug_LogMsgArg("%d, %d - %d %s", len, Sound.samples_left_to_input,
// Sound.samples_left_to_output,
// Sound.samples_left_to_output
// > Sound.samples_left_to_input - (GB_BUFFER_SAMPLES / 2) ?
// "SLOW" : "FAST");
size_t copy_size = (available_size < buffer_size) ?
available_size : buffer_size;

s16 *writebuffer = (s16 *)buffer;
memcpy(buffer, Sound.buffer, copy_size);

if (Sound.samples_left_to_output < len / 4)
return;

Sound.samples_left_to_input += len / 4;
Sound.samples_left_to_output -= len / 4;
// Reset pointer
Sound.buffer_write_ptr = 0;

for (int i = 0; i < len / 2; i++)
{
writebuffer[i] = Sound.buffer[Sound.buffer_next_output_sample++];
Sound.buffer_next_output_sample &= GB_BUFFER_SAMPLES - 1;
}
return copy_size;
}

void GB_SoundResetBufferPointers(void)
{
Sound.buffer_next_input_sample = 0;
Sound.buffer_next_output_sample = 0;
Sound.samples_left_to_input = GB_BUFFER_SAMPLES;
Sound.samples_left_to_output = 0;
Sound.buffer_write_ptr = 0;
}

void GB_SoundInit(void)
Expand Down Expand Up @@ -397,17 +382,10 @@ void GB_SoundMix(void)
if (EmulatorConfig.snd_mute)
return;

if (Sound.samples_left_to_input < 1)
return;

Sound.samples_left_to_input--;
Sound.samples_left_to_output++;

if (Sound.master_enable == 0)
{
Sound.buffer[Sound.buffer_next_input_sample++] = 0;
Sound.buffer[Sound.buffer_next_input_sample++] = 0;
Sound.buffer_next_input_sample &= GB_BUFFER_SAMPLES - 1;
Sound.buffer[Sound.buffer_write_ptr++] = 0;
Sound.buffer[Sound.buffer_write_ptr++] = 0;
return;
}
#if 0
Expand Down Expand Up @@ -436,15 +414,15 @@ void GB_SoundMix(void)
if (Sound.Chn1.running && (EmulatorConfig.chn_flags & 0x1))
{
int index = (((Sound.Chn1.samplecount++) * ((Sound.Chn1.outfreq)
* (32 / 2))) / 22050) & 31;
* (32 / 2))) / GB_SAMPLE_RATE) & 31;
int out_1 = (int)GB_SquareWave[Sound.Chn1.duty][index];
outvalue_left += out_1 * Sound.leftvol_1;
outvalue_right += out_1 * Sound.rightvol_1;
}
if (Sound.Chn2.running && (EmulatorConfig.chn_flags & 0x2))
{
int index = (((Sound.Chn2.samplecount++) * ((Sound.Chn2.outfreq)
* (32 / 2))) / 22050) & 31;
* (32 / 2))) / GB_SAMPLE_RATE) & 31;

int out_2 = (int)GB_SquareWave[Sound.Chn2.duty][index];
outvalue_left += out_2 * Sound.leftvol_2;
Expand All @@ -453,15 +431,15 @@ void GB_SoundMix(void)
if (Sound.Chn3.running && (EmulatorConfig.chn_flags & 0x4))
{
int index = (((Sound.Chn3.samplecount++) * ((Sound.Chn3.outfreq)
* (32 / 2))) / 22050) & 31;
* (32 / 2))) / GB_SAMPLE_RATE) & 31;
int out_3 = (int)GB_WavePattern[index];
outvalue_left += out_3 * Sound.leftvol_3;
outvalue_right += out_3 * Sound.rightvol_3;
}
if (Sound.Chn4.running && (EmulatorConfig.chn_flags & 0x8))
{
int out_4;
int value = ((Sound.Chn4.samplecount++) * Sound.Chn4.outfreq / 2) / 22050;
int value = ((Sound.Chn4.samplecount++) * Sound.Chn4.outfreq / 2) / GB_SAMPLE_RATE;

if (Sound.Chn4.width_7) // 7 bit
{
Expand All @@ -488,17 +466,15 @@ void GB_SoundMix(void)
else if (outvalue_right < (-32768))
outvalue_right = -32768;

Sound.buffer[Sound.buffer_next_input_sample++] =
(outvalue_left * EmulatorConfig.volume) / 128;
Sound.buffer[Sound.buffer_next_input_sample++] =
(outvalue_right * EmulatorConfig.volume) / 128;
Sound.buffer_next_input_sample &= GB_BUFFER_SAMPLES - 1;
outvalue_left = (outvalue_left * EmulatorConfig.volume) / 128;
outvalue_right = (outvalue_right * EmulatorConfig.volume) / 128;

Sound.buffer[Sound.buffer_write_ptr++] = outvalue_left;
Sound.buffer[Sound.buffer_write_ptr++] = outvalue_right;
}

void GB_SoundRegWrite(u32 address, u32 value)
{
//fprintf(stdout, "%04x - %02x\r\n", address, value);

_GB_MEMORY_ *mem = &GameBoy.Memory;

if (Sound.master_enable == 0)
Expand Down Expand Up @@ -927,35 +903,21 @@ void GB_SoundUpdateClocksCounterReference(int reference_clocks)

int increment_clocks = reference_clocks - GB_SoundClockCounterGet();

// Every 16384 clocks update hardware, every ~190 generate output
// Every 16384 clocks update hardware, every 128 generate sample

Sound.clocks += increment_clocks;

if (output_enabled)
{
Sound.nextsample_clocks += increment_clocks;

// This is an ugly hack to make sound buffer not overflow or underflow
// 4194304 Hz CPU / 32768 Hz sound output = 128

// 4194304 Hz CPU / 22050 Hz sound output.
if (Sound.samples_left_to_output >
Sound.samples_left_to_input - (GB_BUFFER_SAMPLES / 2))
{
u32 clocks_ref = (191 + 4) << GameBoy.Emulator.DoubleSpeed;
if (Sound.nextsample_clocks > clocks_ref)
{
Sound.nextsample_clocks -= clocks_ref;
GB_SoundMix();
}
}
else
u32 clocks_ref = 128 << GameBoy.Emulator.DoubleSpeed;
if (Sound.nextsample_clocks > clocks_ref)
{
u32 clocks_ref = (191 - 4) << GameBoy.Emulator.DoubleSpeed;
if (Sound.nextsample_clocks > clocks_ref)
{
Sound.nextsample_clocks -= clocks_ref;
GB_SoundMix();
}
Sound.nextsample_clocks -= clocks_ref;
GB_SoundMix();
}
}

Expand Down
3 changes: 2 additions & 1 deletion source/gb_core/sound.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,8 @@ void GB_SoundUpdate(u32 clocks);
void GB_SoundRegWrite(u32 address, u32 value);
void GB_SoundResetBufferPointers(void);
void GB_SoundEnd(void);
void GB_SoundCallback(void *buffer, long len);
size_t GB_SoundGetSamplesFrame(void *buffer, size_t buffer_size);
void GB_SoundResetBufferPointers(void);

void GB_SoundClockCounterReset(void);
void GB_SoundUpdateClocksCounterReference(int reference_clocks);
Expand Down
96 changes: 29 additions & 67 deletions source/gba_core/sound.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,8 @@
#define GBA_BUFFER_SIZE (16384)
#define GBA_BUFFER_SAMPLES (GBA_BUFFER_SIZE / 2)

#define GBA_SAMPLE_RATE (32 * 1024)

static const s8 GBA_SquareWave[4][32] = {
{ -128, -128, -128, -128, -128, -128, -128, -128,
127, 127, -128, -128, -128, -128, -128, -128,
Expand Down Expand Up @@ -208,11 +210,9 @@ typedef struct
int PSG_master_volume;

u32 nextsample_clocks;
s16 buffer[GBA_BUFFER_SIZE / 2];
u32 buffer_next_input_sample;
u32 buffer_next_output_sample;
int samples_left_to_input;
int samples_left_to_output;

s16 buffer[GBA_SAMPLE_RATE];
u32 buffer_write_ptr;

// Some temporary variables to avoid doing the same calculations every time
// a sample is going to be generated:
Expand Down Expand Up @@ -312,42 +312,27 @@ void GBA_SoundPowerOn(void)
//GBA_SoundRegWrite16(SOUNDBIAS, 0);
}

void GBA_SoundCallback(void *buffer, long len)
// This function is supposed to return all the samples taken during a frame. If
// the destination buffer isn't big enough, it will clear the source buffer
// anyway, to prepare it for next frame.
size_t GBA_SoundGetSamplesFrame(void *buffer, size_t buffer_size)
{
if (output_enabled == 0)
{
memset(buffer, 0, len);
return;
}
size_t available_size = Sound.buffer_write_ptr * 2;

// Should print: (GBA_BUFFER_SAMPLES / 3 * 2) - (GBA_BUFFER_SAMPLES / 3)
//Debug_LogMsgArg("%d, %d - %d %s", len,
// Sound.samples_left_to_input, Sound.samples_left_to_output,
// Sound.samples_left_to_output
// > Sound.samples_left_to_input - (GBA_BUFFER_SAMPLES / 2) ?
// "SLOW" : "FAST");
size_t copy_size = (available_size < buffer_size) ?
available_size : buffer_size;

s16 *writebuffer = (s16 *)buffer;
memcpy(buffer, Sound.buffer, copy_size);

if (Sound.samples_left_to_output < len / 4)
return;

Sound.samples_left_to_input += len / 4;
Sound.samples_left_to_output -= len / 4;
// Reset pointer
Sound.buffer_write_ptr = 0;

for (int i = 0; i < len / 2; i++)
{
writebuffer[i] = Sound.buffer[Sound.buffer_next_output_sample++];
Sound.buffer_next_output_sample &= GBA_BUFFER_SAMPLES - 1;
}
return copy_size;
}

void GBA_SoundResetBufferPointers(void)
{
Sound.buffer_next_input_sample = 0;
Sound.buffer_next_output_sample = 0;
Sound.samples_left_to_input = GBA_BUFFER_SAMPLES;
Sound.samples_left_to_output = 0;
Sound.buffer_write_ptr = 0;
}

void GBA_SoundInit(void)
Expand Down Expand Up @@ -464,17 +449,10 @@ void GBA_SoundMix(void)
if (EmulatorConfig.snd_mute)
return;

if (Sound.samples_left_to_input < 1)
return;

Sound.samples_left_to_input--;
Sound.samples_left_to_output++;

if (Sound.master_enable == 0)
{
Sound.buffer[Sound.buffer_next_input_sample++] = 0;
Sound.buffer[Sound.buffer_next_input_sample++] = 0;
Sound.buffer_next_input_sample &= GBA_BUFFER_SAMPLES - 1;
Sound.buffer[Sound.buffer_write_ptr++] = 0;
Sound.buffer[Sound.buffer_write_ptr++] = 0;
return;
}

Expand Down Expand Up @@ -565,14 +543,14 @@ void GBA_SoundMix(void)
outvalue_left >>= 1;
outvalue_right >>= 1;

Sound.buffer[Sound.buffer_next_input_sample++] =
(outvalue_left * EmulatorConfig.volume) / 128;
Sound.buffer[Sound.buffer_next_input_sample++] =
(outvalue_right * EmulatorConfig.volume) / 128;
Sound.buffer_next_input_sample &= GBA_BUFFER_SAMPLES - 1;
outvalue_left = (outvalue_left * EmulatorConfig.volume) / 128;
outvalue_right = (outvalue_right * EmulatorConfig.volume) / 128;

Sound.buffer[Sound.buffer_write_ptr++] = outvalue_left;
Sound.buffer[Sound.buffer_write_ptr++] = outvalue_right;
}

// Every 65535 clocks update hardware, every ~512 generate output
// Every 65535 clocks update hardware, every 512 generate sample
u32 GBA_SoundUpdate(u32 clocks)
{
Sound.clocks += clocks;
Expand All @@ -581,28 +559,12 @@ u32 GBA_SoundUpdate(u32 clocks)
{
Sound.nextsample_clocks += clocks;

// 16777216 Hz?
// 16777216 Hz CPU / 32768 Hz sound output = 512

// 16.78 MHz CPU / 22050 = 761
// 16.78 MHz CPU / 32768 Hz sound output = 512

//This is an ugly hack to make sound buffer not overflow or underflow...
if (Sound.samples_left_to_output
> Sound.samples_left_to_input - (GBA_BUFFER_SAMPLES / 2))
{
if (Sound.nextsample_clocks > (761 + 10))
{
Sound.nextsample_clocks -= (761 + 10);
GBA_SoundMix();
}
}
else
if (Sound.nextsample_clocks > 512)
{
if (Sound.nextsample_clocks > (761 - 10))
{
Sound.nextsample_clocks -= (761 - 10);
GBA_SoundMix();
}
Sound.nextsample_clocks -= 512;
GBA_SoundMix();
}
}

Expand Down
2 changes: 1 addition & 1 deletion source/gba_core/sound.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -14,9 +14,9 @@ int GBA_SoundHardwareIsOn(void);
void GB_ToggleSound(void);
u32 GBA_SoundUpdate(u32 clocks);
void GBA_SoundRegWrite16(u32 address, u16 value);
size_t GBA_SoundGetSamplesFrame(void *buffer, size_t buffer_size);
void GBA_SoundResetBufferPointers(void);
void GBA_SoundEnd(void);
void GBA_SoundCallback(void *buffer, long len);
void GBA_SoundTimerCheck(u32 number);

void GBA_SoundGetConfig(int *vol, int *chn_flags);
Expand Down
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