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Fixed bug 4710 - audio/alsa: avoid configuring hardware parameters wi…
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…th only a single period

Anthony Pesch

The previous code first configured the period size using snd_pcm_hw_par-
ams_set_period_size_near. Then, it further narrowed the configuration
space by calling snd_pcm_hw_params_set_buffer_size_near using a buffer
size of 2 times the _requested_ period size in order to try and get a
configuration with only 2 periods. If the configured period size was
larger than the requested size, the second call could inadvertently
narrow the configuration space to contain only a single period.

Rather than fixing the call to snd_pcm_hw_params_set_buffer_size_near
to use a size of 2 times the configured period size, the code has been
changed to use snd_pcm_hw_params_set_periods_min in order to more
clearly explain the intent.
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@slouken
slouken committed Jul 7, 2019
1 parent 67bb882 commit 680e793
Showing 1 changed file with 19 additions and 10 deletions.
29 changes: 19 additions & 10 deletions src/audio/alsa/SDL_alsa_audio.c
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Expand Up @@ -72,7 +72,9 @@ static int (*ALSA_snd_pcm_hw_params_set_period_size_near)
(snd_pcm_t *, snd_pcm_hw_params_t *, snd_pcm_uframes_t *, int *);
static int (*ALSA_snd_pcm_hw_params_get_period_size)
(const snd_pcm_hw_params_t *, snd_pcm_uframes_t *, int *);
static int (*ALSA_snd_pcm_hw_params_set_periods_near)
static int (*ALSA_snd_pcm_hw_params_set_periods_min)
(snd_pcm_t *, snd_pcm_hw_params_t *, unsigned int *, int *);
static int (*ALSA_snd_pcm_hw_params_set_periods_first)
(snd_pcm_t *, snd_pcm_hw_params_t *, unsigned int *, int *);
static int (*ALSA_snd_pcm_hw_params_get_periods)
(const snd_pcm_hw_params_t *, unsigned int *, int *);
Expand Down Expand Up @@ -148,7 +150,8 @@ load_alsa_syms(void)
SDL_ALSA_SYM(snd_pcm_hw_params_set_rate_near);
SDL_ALSA_SYM(snd_pcm_hw_params_set_period_size_near);
SDL_ALSA_SYM(snd_pcm_hw_params_get_period_size);
SDL_ALSA_SYM(snd_pcm_hw_params_set_periods_near);
SDL_ALSA_SYM(snd_pcm_hw_params_set_periods_min);
SDL_ALSA_SYM(snd_pcm_hw_params_set_periods_first);
SDL_ALSA_SYM(snd_pcm_hw_params_get_periods);
SDL_ALSA_SYM(snd_pcm_hw_params_set_buffer_size_near);
SDL_ALSA_SYM(snd_pcm_hw_params_get_buffer_size);
Expand Down Expand Up @@ -462,25 +465,31 @@ ALSA_set_buffer_size(_THIS, snd_pcm_hw_params_t *params)
{
int status;
snd_pcm_hw_params_t *hwparams;
snd_pcm_uframes_t bufsize;
snd_pcm_uframes_t persize;
unsigned int periods;

/* Copy the hardware parameters for this setup */
snd_pcm_hw_params_alloca(&hwparams);
ALSA_snd_pcm_hw_params_copy(hwparams, params);

/* Prioritize matching the period size to the requested buffer size */
/* Attempt to match the period size to the requested buffer size */
persize = this->spec.samples;
status = ALSA_snd_pcm_hw_params_set_period_size_near(
this->hidden->pcm_handle, hwparams, &persize, NULL);
if ( status < 0 ) {
return(-1);
}

/* Next try to restrict the parameters to having only two periods */
bufsize = this->spec.samples * 2;
status = ALSA_snd_pcm_hw_params_set_buffer_size_near(
this->hidden->pcm_handle, hwparams, &bufsize);
/* Need to at least double buffer */
periods = 2;
status = ALSA_snd_pcm_hw_params_set_periods_min(
this->hidden->pcm_handle, hwparams, &periods, NULL);
if ( status < 0 ) {
return(-1);
}

status = ALSA_snd_pcm_hw_params_set_periods_first(
this->hidden->pcm_handle, hwparams, &periods, NULL);
if ( status < 0 ) {
return(-1);
}
Expand All @@ -495,9 +504,9 @@ ALSA_set_buffer_size(_THIS, snd_pcm_hw_params_t *params)

/* This is useful for debugging */
if ( SDL_getenv("SDL_AUDIO_ALSA_DEBUG") ) {
unsigned int periods = 0;
snd_pcm_uframes_t bufsize;

ALSA_snd_pcm_hw_params_get_periods(hwparams, &periods, NULL);
ALSA_snd_pcm_hw_params_get_buffer_size(hwparams, &bufsize);

fprintf(stderr,
"ALSA: period size = %ld, periods = %u, buffer size = %lu\n",
Expand Down

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