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Add alsa async code example

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Laurens Miers 2020-05-27 14:26:54 +02:00
parent 696d0eeb3a
commit 3a5559663e
1 changed files with 60 additions and 1 deletions
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61
alsa_info.md
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@ -572,9 +572,68 @@ int main(int argc, char **argv)
||| |||
#### Async #### Async
```c ```c
#define AUDIO_SAMPLERATE 16000
#define AUDIO_NR_OF_SAMPLES 128u
#define AUDIO_BYTES_PER_SAMPLE 2u
#define AUDIO_OUTPUT_NR_CHANNELS 2u
#define SAMPLE_BUFFER_SIZE (AUDIO_NR_OF_SAMPLES * AUDIO_OUTPUT_NR_CHANNELS * AUDIO_BYTES_PER_SAMPLE)
static void my_signal_callback(snd_async_handler_t *ahandler)
{
snd_pcm_t *pcm_handle = snd_async_handler_get_pcm(ahandler);
void *my_priv_data = snd_async_hanlder_get_callback_private(ahandler);
char my_samples[SAMPLE_BUFFER_SIZE] = { 0 };
snd_pcm_sframes_t avail = 0;
avail = snd_pcm_avail_update(pcm_handle);
if (avail < 0) {
// xrun recovery
}
while (avail >= AUDIO_NR_SAMPLES) {
snd_pcm_writei(pcm_handle, my_samples, AUDIO_NR_SAMPLES);
avail = snd_pcm_avail_update(pcm_handle);
// xrun checking...
}
}
int main(int argc, char **argv) int main(int argc, char **argv)
{ {
//TODO snd_pcm_t *handle = NULL;
snd_async_handler_t *async_handle = NULL;
void *my_priv_data = NULL;
int period_size = 0;
int period_time = 0;
char my_samples[SAMPLE_BUFFER_SIZE];
// Open pcm, non-blocking or blocking, your choice
snd_pcm_open(&handle, "default:CARD=MyAwesomeAudioCard", SND_PCM_STREAM_PLAYBACK, 0);
// Just... for the love of god.... don't use SND_PCM_ASYNC!!!
// snd_pcm_open(&handle, "default:CARD=MyAwesomeAudioCard", SND_PCM_STREAM_PLAYBACK, SND_PCM_ASYNC);
// setup rest of stuff...
// Install callback
snd_pcm_add_pcm_handler(&async_handle, handle, my_signal_callback, NULL);
// Prepare codec for output
snd_pcm_drop(handle); // Just to be sure...
snd_pcm_prepare(handle);
// ALSA gods demand their buffers to be prefilled with 2 period sizes!
snd_pcm_writei(handle, my_samples, AUDIO_NR_OF_SAMPLES);
snd_pcm_writei(handle, my_samples, AUDIO_NR_OF_SAMPLES);
// Codec is started after this
snd_pcm_state(handle) == SND_PCM_STATE_RUNNING;
while(1) {
// everything is handled in callback
sleep(100);
}
} }
``` ```