一个简单的ALSA示例代码

代码如下，注释可参看原文http://users.suse.com/~mana/alsa090_howto.html

#include <alsa/asoundlib.h>

int main()

{

int ret;

snd_pcm_t *pcm_handle;

snd_pcm_stream_t stream = SND_PCM_STREAM_PLAYBACK;

snd_pcm_hw_params_t *hwparams;

char *pcm_name;

pcm_name = strdup("plughw:0,0");

snd_pcm_hw_params_alloca(&hwparams);

ret = snd_pcm_open(&pcm_handle, pcm_name, stream, 0);

if (ret < 0) {

printf("snd_pcm_open failed\n");

return(-1);

}

ret = snd_pcm_hw_params_any(pcm_handle, hwparams);

if (ret < 0) {

printf("snd_pcm_hw_params_any failed\n");

return(-1);

}

int rate = 44100;

int exact_rate;

int dir;

int periods = 2;

snd_pcm_uframes_t periodsize = 8192;

ret = snd_pcm_hw_params_set_access(pcm_handle, hwparams,

SND_PCM_ACCESS_RW_INTERLEAVED);

if (ret < 0) {

printf("snd_pcm_hw_params_set_access failed\n");

return(-1);

}

ret = snd_pcm_hw_params_set_format(pcm_handle, hwparams,

SND_PCM_FORMAT_S16_LE);

if (ret < 0) {

printf("snd_pcm_hw_params_set_format failed\n");

return(-1);

}

exact_rate = rate;

ret = snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams,

&exact_rate, 0);

if (ret < 0) {

printf("snd_pcm_hw_params_set_rate_near failed\n");

return(-1);

}

if (rate != exact_rate) {

printf("The rate %d Hz is not supported by your hardware\n"

"==> Using %d Hz instead\n", rate, exact_rate);

}

ret = snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2);

if (ret < 0) {

printf("snd_pcm_hw_params_set_channels failed\n");

return(-1);

}

ret = snd_pcm_hw_params_set_periods(pcm_handle, hwparams, periods, 0);

if (ret < 0) {

printf("snd_pcm_hw_params_set_periods failed\n");

return(-1);

}

ret = snd_pcm_hw_params_set_buffer_size(pcm_handle, hwparams,

(periodsize * periods) >> 2);

if (ret < 0) {

printf("snd_pcm_hw_params_set_buffer_size failed\n");

return(-1);

}

ret = snd_pcm_hw_params(pcm_handle, hwparams);

if (ret < 0) {

printf("snd_pcm_hw_params failed\n");

return(-1);

}

unsigned char *data;

int l1, l2;

short s1, s2;

int frames;

data = malloc(periodsize);

frames = periodsize >> 2;

for (l1 = 0; l1 < 100; l1++) {

for (l2 = 0; l2 < frames; l2++) {

s1 = (l2 % 128) * 100 - 5000;

s2 = (l2 % 256) * 100 - 5000;

data[4*l2] = (unsigned char)s1;

data[4*l2+1] = s1 >> 8;

data[4*l2+2] = (unsigned char)s2;

data[4*l2+3] = s2 >> 8;

}

while ((ret = snd_pcm_writei(pcm_handle, data, frames)) < 0) {

snd_pcm_prepare(pcm_handle);

printf("<<<<<<<<<<<<<<Buffer Underrun>>>>>>>>>>>>\n");

}

}

snd_pcm_drop(pcm_handle);

snd_pcm_drain(pcm_handle);

return 0;

}