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Switched from setting the period size and count to setting the buffer…
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… size directly, based on feedback from the ALSA development list:

http://mailman.alsa-project.org/pipermail/alsa-devel/2009-October/022267.html

This has the nice side effect of reducing latency on my SBLive! card.
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@slouken
slouken committed Oct 13, 2009
1 parent fb4784d commit ce1e75c
Showing 1 changed file with 22 additions and 12 deletions.
34 changes: 22 additions & 12 deletions src/audio/alsa/SDL_alsa_audio.c
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Expand Up @@ -46,6 +46,10 @@
/* The default ALSA audio driver */
#define DEFAULT_DEVICE "default"

/* Whether we should set the buffer size or the period size */
/*#define SET_PERIOD_SIZE*/
/*#define DEBUG_PERIOD_SIZE*/

/* Audio driver functions */
static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec);
static void ALSA_WaitAudio(_THIS);
Expand Down Expand Up @@ -78,13 +82,13 @@ static int (*SDL_NAME(snd_pcm_hw_params_set_period_size_near))(snd_pcm_t *pcm, s
static int (*SDL_NAME(snd_pcm_hw_params_get_period_size))(const snd_pcm_hw_params_t *params, snd_pcm_uframes_t *frames, int *dir);
static int (*SDL_NAME(snd_pcm_hw_params_set_periods_near))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, unsigned int *val, int *dir);
static int (*SDL_NAME(snd_pcm_hw_params_get_periods))(const snd_pcm_hw_params_t *params, unsigned int *val, int *dir);
static int (*SDL_NAME(snd_pcm_hw_params_set_buffer_size_near))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params, snd_pcm_uframes_t *val);
static int (*SDL_NAME(snd_pcm_hw_params_get_buffer_size))(const snd_pcm_hw_params_t *params, snd_pcm_uframes_t *val);
static int (*SDL_NAME(snd_pcm_hw_params))(snd_pcm_t *pcm, snd_pcm_hw_params_t *params);
/*
*/
static int (*SDL_NAME(snd_pcm_sw_params_current))(snd_pcm_t *pcm, snd_pcm_sw_params_t *swparams);
static int (*SDL_NAME(snd_pcm_sw_params_set_start_threshold))(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val);
static int (*SDL_NAME(snd_pcm_sw_params_set_avail_min))(snd_pcm_t *pcm, snd_pcm_sw_params_t *params, snd_pcm_uframes_t val);
static int (*SDL_NAME(snd_pcm_sw_params))(snd_pcm_t *pcm, snd_pcm_sw_params_t *params);
static int (*SDL_NAME(snd_pcm_nonblock))(snd_pcm_t *pcm, int nonblock);
#define snd_pcm_hw_params_sizeof SDL_NAME(snd_pcm_hw_params_sizeof)
Expand Down Expand Up @@ -114,11 +118,11 @@ static struct {
{ "snd_pcm_hw_params_get_period_size", (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_period_size) },
{ "snd_pcm_hw_params_set_periods_near", (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_periods_near) },
{ "snd_pcm_hw_params_get_periods", (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_periods) },
{ "snd_pcm_hw_params_set_buffer_size_near", (void**)(char*)&SDL_NAME(snd_pcm_hw_params_set_buffer_size_near) },
{ "snd_pcm_hw_params_get_buffer_size", (void**)(char*)&SDL_NAME(snd_pcm_hw_params_get_buffer_size) },
{ "snd_pcm_hw_params", (void**)(char*)&SDL_NAME(snd_pcm_hw_params) },
{ "snd_pcm_sw_params_current", (void**)(char*)&SDL_NAME(snd_pcm_sw_params_current) },
{ "snd_pcm_sw_params_set_start_threshold", (void**)(char*)&SDL_NAME(snd_pcm_sw_params_set_start_threshold) },
{ "snd_pcm_sw_params_set_avail_min", (void**)(char*)&SDL_NAME(snd_pcm_sw_params_set_avail_min) },
{ "snd_pcm_sw_params", (void**)(char*)&SDL_NAME(snd_pcm_sw_params) },
{ "snd_pcm_nonblock", (void**)(char*)&SDL_NAME(snd_pcm_nonblock) },
};
Expand Down Expand Up @@ -368,8 +372,10 @@ static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec)
snd_pcm_format_t format;
snd_pcm_uframes_t frames;
unsigned int rate;
#ifdef SET_PERIOD_SIZE
unsigned int periods;
unsigned int channels;
#endif
unsigned int channels;
Uint16 test_format;

/* Open the audio device */
Expand Down Expand Up @@ -464,18 +470,28 @@ static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec)
spec->freq = rate;

/* Set the buffer size, in samples */
#ifdef SET_PERIOD_SIZE
frames = spec->samples;
status = SDL_NAME(snd_pcm_hw_params_set_period_size_near)(pcm_handle, hwparams, &frames, NULL);
if ( status < 0 ) {
SDL_SetError("Couldn't set audio frequency: %s", SDL_NAME(snd_strerror)(status));
SDL_SetError("Couldn't set period size: %s", SDL_NAME(snd_strerror)(status));
ALSA_CloseAudio(this);
return(-1);
}

spec->samples = frames;

periods = 2;
SDL_NAME(snd_pcm_hw_params_set_periods_near)(pcm_handle, hwparams, &periods, NULL);
status = SDL_NAME(snd_pcm_hw_params_set_periods_near)(pcm_handle, hwparams, &periods, NULL);
if ( status < 0 ) {
SDL_SetError("Couldn't set period count: %s", SDL_NAME(snd_strerror)(status));
ALSA_CloseAudio(this);
return(-1);
}
#else
frames = spec->samples * 2;
status = SDL_NAME(snd_pcm_hw_params_set_buffer_size_near)(pcm_handle, hwparams, &frames);
#endif

/* "set" the hardware with the desired parameters */
status = SDL_NAME(snd_pcm_hw_params)(pcm_handle, hwparams);
Expand All @@ -486,7 +502,7 @@ static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec)
}

/* This is useful for debugging... */
#if 0
#ifdef DEBUG_PERIOD_SIZE
{ snd_pcm_uframes_t bufsize; snd_pcm_sframes_t persize; unsigned int periods; int dir;
SDL_NAME(snd_pcm_hw_params_get_buffer_size)(hwparams, &bufsize);
SDL_NAME(snd_pcm_hw_params_get_period_size)(hwparams, &persize, &dir);
Expand All @@ -510,12 +526,6 @@ static int ALSA_OpenAudio(_THIS, SDL_AudioSpec *spec)
ALSA_CloseAudio(this);
return(-1);
}
status = SDL_NAME(snd_pcm_sw_params_set_avail_min)(pcm_handle, swparams, frames);
if ( status < 0 ) {
SDL_SetError("Couldn't set avail min: %s", SDL_NAME(snd_strerror)(status));
ALSA_CloseAudio(this);
return(-1);
}
status = SDL_NAME(snd_pcm_sw_params)(pcm_handle, swparams);
if ( status < 0 ) {
SDL_SetError("Couldn't set software audio parameters: %s", SDL_NAME(snd_strerror)(status));
Expand Down

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