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alsa: set minimum period count before automatic period size

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Some devices (FireWire) fail to produce audio if period count is < 3,
and also have small buffer size. When quantum is too large, we might
then get too few periods and broken sound.

Set minimum for the period count in ALSA, to determine the maximum
period size we can use. If smaller than what we were going to use, round
down to power-of-2.

See #4785
This commit is contained in:
Pauli Virtanen 2025-09-06 16:06:53 +03:00 • committed by Wim Taymans
parent 7a98bcf735
commit 64aaf8a832
1 changed files with 30 additions and 11 deletions
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41
spa/plugins/alsa/alsa-pcm.c
View file

@ -2328,6 +2328,35 @@ int spa_alsa_set_format(struct state *state, struct spa_audio_info *fmt, uint32_
}
}
if (state->default_period_num != 0) {
/* period number given use that */
periods = state->default_period_num;
} else if (state->disable_tsched) {
/* IRQ mode, use 3 periods. This is a bit of a workaround
* for Firewire devices, which seem to only work with 3 periods.
* For PipeWire it does not actually matter how many periods
* are used, we will always keep 1 filled, so we can work fine
* with anything from 2 periods to MAX. */
periods = 3;
} else {
periods = UINT_MAX;
}
if (state->default_period_size == 0) {
/* Some devices (FireWire) don't produce audio if period number is too
* small, so force a minimum. This will restrict possible period sizes if
* the device has small buffer (like FireWire), so force it only if
* period size was not set manually.
*/
snd_pcm_uframes_t period_size_max;
unsigned int periods_min = (periods == UINT_MAX) ? 3 : periods;
CHECK(snd_pcm_hw_params_set_periods_min(hndl, params, &periods_min, &dir), "set_periods_min");
CHECK(snd_pcm_hw_params_get_period_size_max(params, &period_size_max, &dir), "get_period_size_max");
if (period_size > period_size_max)
period_size = SPA_MIN(period_size, flp2(period_size_max));
}
CHECK(snd_pcm_hw_params_set_period_size_near(hndl, params, &period_size, &dir), "set_period_size_near");
if (period_size == 0) {
@ -2337,17 +2366,7 @@ int spa_alsa_set_format(struct state *state, struct spa_audio_info *fmt, uint32_
state->period_frames = period_size;
if (state->default_period_num != 0 || state->disable_tsched) {
if (state->default_period_num != 0)
/* period number given use that */
periods = state->default_period_num;
else
/* IRQ mode, use 3 periods. This is a bit of a workaround
* for Firewire devices, which seem to only work with 3 periods.
* For PipeWire it does not actually matter how many periods
* are used, we will always keep 1 filled, so we can work fine
* with anything from 2 periods to MAX. */
periods = 3;
if (periods != UINT_MAX) {
CHECK(snd_pcm_hw_params_set_periods_near(hndl, params, &periods, &dir), "set_periods");
state->buffer_frames = period_size * periods;
} else {