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alsa: use position duration as period size

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Use half of the configured quantum as the period size in batch mode.
This gives lower latency for USB devices depending on the quantum.
This commit is contained in:
Wim Taymans 2021-12-17 16:08:08 +01:00
parent 15ce86aff1
commit 8630b8846c
2 changed files with 6 additions and 1 deletions
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6
spa/plugins/alsa/alsa-pcm.c
View file

@ -1327,17 +1327,21 @@ int spa_alsa_set_format(struct state *state, struct spa_audio_info *fmt, uint32_
state->card->rate = rrate;
dir = 0;
period_size = state->default_period_size ? state->default_period_size : 1024;
period_size = state->default_period_size;
is_batch = snd_pcm_hw_params_is_batch(params) &&
!state->disable_batch;
if (is_batch) {
if (period_size == 0)
period_size = state->position ? state->position->clock.duration : DEFAULT_PERIOD;
/* batch devices get their hw pointers updated every period. Make
* the period smaller and add one period of headroom */
period_size /= 2;
spa_log_info(state->log, "%s: batch mode, period_size:%ld",
state->props.device, period_size);
} else {
if (period_size == 0)
period_size = DEFAULT_PERIOD;
/* disable ALSA wakeups, we use a timer */
if (snd_pcm_hw_params_can_disable_period_wakeup(params))
CHECK(snd_pcm_hw_params_set_period_wakeup(hndl, params, 0), "set_period_wakeup");

1
spa/plugins/alsa/alsa-pcm.h
View file

@ -55,6 +55,7 @@ extern "C" {
#define MIN_LATENCY 16
#define MAX_LATENCY 8192
#define DEFAULT_PERIOD 1024u
#define DEFAULT_RATE 48000u
#define DEFAULT_CHANNELS 2u
#define DEFAULT_USE_CHMAP false