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#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <poll.h>
#include <alsa/asoundlib.h>
snd_pcm_t *playback_handle;
short buf[4096];
int
playback_callback (snd_pcm_sframes_t nframes)
{
int err;
printf ("playback callback called with %u frames\n", nframes);
/* ... fill buf with data ... */
if ((err = snd_pcm_writei (playback_handle, buf, nframes)) < 0) {
fprintf (stderr, "write failed (%s)\n", snd_strerror (err));
}
return err;
}
main (int argc, char *argv[])
{
snd_pcm_hw_params_t *hw_params;
snd_pcm_sw_params_t *sw_params;
snd_pcm_sframes_t frames_to_deliver;
int nfds;
int err;
struct pollfd *pfds;
if ((err = snd_pcm_open (&playback_handle, argv[1], SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
fprintf (stderr, "cannot open audio device %s (%s)\n",
argv[1],
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_hw_params_malloc (&hw_params)) < 0) {
fprintf (stderr, "cannot allocate hardware parameter structure (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_hw_params_any (playback_handle, hw_params)) < 0) {
fprintf (stderr, "cannot initialize hardware parameter structure (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_hw_params_set_access (playback_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
fprintf (stderr, "cannot set access type (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_hw_params_set_format (playback_handle, hw_params, SND_PCM_FORMAT_S16_LE)) < 0) {
fprintf (stderr, "cannot set sample format (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_hw_params_set_rate_near (playback_handle, hw_params, 44100, 0)) < 0) {
fprintf (stderr, "cannot set sample rate (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_hw_params_set_channels (playback_handle, hw_params, 2)) < 0) {
fprintf (stderr, "cannot set channel count (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_hw_params (playback_handle, hw_params)) < 0) {
fprintf (stderr, "cannot set parameters (%s)\n",
snd_strerror (err));
exit (1);
}
snd_pcm_hw_params_free (hw_params);
/* tell ALSA to wake us up whenever 4096 or more frames
of playback data can be delivered. Also, tell
ALSA that we'll start the device ourselves.
*/
if ((err = snd_pcm_sw_params_malloc (&sw_params)) < 0) {
fprintf (stderr, "cannot allocate software parameters structure (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_sw_params_current (playback_handle, sw_params)) < 0) {
fprintf (stderr, "cannot initialize software parameters structure (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_sw_params_set_avail_min (playback_handle, sw_params, 4096)) < 0) {
fprintf (stderr, "cannot set minimum available count (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_sw_params_set_start_threshold (playback_handle, sw_params, 0U)) < 0) {
fprintf (stderr, "cannot set start mode (%s)\n",
snd_strerror (err));
exit (1);
}
if ((err = snd_pcm_sw_params (playback_handle, sw_params)) < 0) {
fprintf (stderr, "cannot set software parameters (%s)\n",
snd_strerror (err));
exit (1);
}
/* the interface will interrupt the kernel every 4096 frames, and ALSA
will wake up this program very soon after that.
*/
if ((err = snd_pcm_prepare (playback_handle)) < 0) {
fprintf (stderr, "cannot prepare audio interface for use (%s)\n",
snd_strerror (err));
exit (1);
}
while (1) {
/* wait till the interface is ready for data, or 1 second
has elapsed.
*/
if ((err = snd_pcm_wait (playback_handle, 1000)) < 0) {
fprintf (stderr, "poll failed (%s)\n", strerror (errno));
break;
}
/* find out how much space is available for playback data */
if ((frames_to_deliver = snd_pcm_avail_update (playback_handle)) < 0) {
if (frames_to_deliver == -EPIPE) {
fprintf (stderr, "an xrun occured\n");
break;
} else {
fprintf (stderr, "unknown ALSA avail update return value (%d)\n",
frames_to_deliver);
break;
}
}
frames_to_deliver = frames_to_deliver > 4096 ? 4096 : frames_to_deliver;
/* deliver the data */
if (playback_callback (frames_to_deliver) != frames_to_deliver) {
fprintf (stderr, "playback callback failed\n");
break;
}
}
snd_pcm_close (playback_handle);
exit (0);
}