Fixed bug 4710 - audio/alsa: avoid configuring hardware parameters with 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.
diff --git a/src/audio/alsa/SDL_alsa_audio.c b/src/audio/alsa/SDL_alsa_audio.c
index 9364fc1..b65de78 100644
--- a/src/audio/alsa/SDL_alsa_audio.c
+++ b/src/audio/alsa/SDL_alsa_audio.c
@@ -72,7 +72,9 @@
(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 *);
@@ -148,7 +150,8 @@
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);
@@ -462,14 +465,14 @@
{
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);
@@ -477,10 +480,16 @@
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);
}
@@ -495,9 +504,9 @@
/* 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",
