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ALSA: Improvements buffer size negotiation.

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This makes it so period sizes are a power of 2, which in turns makes it
so the value set by `snd_pcm_sw_params_set_avail_min()` is also a power
of 2. This is inline with a suggestion by the ALSA documentation, and
seems to have an actual positive impact in practice with my testing as
well.
This commit is contained in:
David Reid
2026-01-09 15:37:05 +10:00
parent 46adfae3bb
commit e9eccf49a3
1 changed files with 17 additions and 2 deletions
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miniaudio.h
+17 -2
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@@ -29319,7 +29319,22 @@ static ma_result ma_device_init_by_type__alsa(ma_context* pContext, ma_context_s
/* Buffer Size */
{
ma_snd_pcm_uframes_t actualBufferSizeInFrames = ma_calculate_buffer_size_in_frames_from_descriptor(pDescriptor, internalSampleRate) * internalPeriods;
ma_snd_pcm_uframes_t actualBufferSizeInFrames;
/*
Down below when we configure our software parameters we'll be setting snd_pcm_sw_params_set_avail_min() to
a value equal to a single period. The ALSA documentation says the following:
The valid values for ‘val’ are determined by the specific hardware. Most PC sound cards can only accept
power of 2 frame counts (i.e. 512, 1024, 2048). You cannot use this as a high resolution timer - it is
limited to how often the sound card hardware raises an interrupt.
For this reason I'm going to be forcing periods to a power of 2. I've noticed in practice that this does
indeed seem to make an actual real-world difference. If I set it to, say, 96 frames per period, I will fairly
frequently get horrible glitching in duplex mode, almost as if the buffer is stuck straddling the end of a
buffer. So far I've had no such issues when setting to something like 64.
*/
actualBufferSizeInFrames = ma_prev_power_of_2(ma_calculate_buffer_size_in_frames_from_descriptor(pDescriptor, internalSampleRate)) * internalPeriods;
resultALSA = pContextStateALSA->snd_pcm_hw_params_set_buffer_size_near(pPCM, pHWParams, &actualBufferSizeInFrames);
if (resultALSA < 0) {
@@ -29348,7 +29363,7 @@ static ma_result ma_device_init_by_type__alsa(ma_context* pContext, ma_context_s
continue;
}
resultALSA = pContextStateALSA->snd_pcm_sw_params_set_avail_min(pPCM, pSWParams, ma_prev_power_of_2(internalPeriodSizeInFrames));
resultALSA = pContextStateALSA->snd_pcm_sw_params_set_avail_min(pPCM, pSWParams, internalPeriodSizeInFrames);
if (resultALSA < 0) {
pContextStateALSA->snd_pcm_close(pPCM);
ma_log_postf(ma_context_get_log(pContext), MA_LOG_LEVEL_ERROR, "[ALSA] snd_pcm_sw_params_set_avail_min() failed for device \"%s\".", pDeviceName);