Hello world ALSA

hello_alsa.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <alsa/asoundlib.h>

/* code from http://www.suse.de/~mana/alsa090_howto.html */
/* Link it with -lasound */
/* Needs pkg 'libasound2-dev' installed */

/* Handle for the PCM device */ 
snd_pcm_t *pcm_handle;          

/* Playback stream */
snd_pcm_stream_t stream = SND_PCM_STREAM_PLAYBACK;

/* This structure contains information about    */
/* the hardware and can be used to specify the  */      
/* configuration to be used for the PCM stream. */ 
snd_pcm_hw_params_t *hwparams;

/* Name of the PCM device, like plughw:0,0          */
/* The first number is the number of the soundcard, */
/* the second number is the number of the device.   */
char *pcm_name;

int main(int argc, char *argv[])
{

pcm_name = argv[1];
/* pcm_name = strdup("hw:0.0");  */

/* Allocate the snd_pcm_hw_params_t structure on the stack. */
snd_pcm_hw_params_alloca(&hwparams);

/* Open PCM. The last parameter of this function is the mode. */
/* If this is set to 0, the standard mode is used. Possible   */
/* other values are SND_PCM_NONBLOCK and SND_PCM_ASYNC.       */ 
/* If SND_PCM_NONBLOCK is used, read / write access to the    */
/* PCM device will return immediately. If SND_PCM_ASYNC is    */
/* specified, SIGIO will be emitted whenever a period has     */
/* been completely processed by the soundcard.                */
if (snd_pcm_open(&pcm_handle, pcm_name, stream, 0) < 0) {
  fprintf(stderr, "Error opening PCM device %s\n", pcm_name);
  return(-1);
}

/* Init hwparams with full configuration space */
if (snd_pcm_hw_params_any(pcm_handle, hwparams) < 0) {
  fprintf(stderr, "Can not configure this PCM device.\n");
  return(-1);
}

int rate = 44100;
int exact_rate;   /* Sample rate returned by */
              /* snd_pcm_hw_params_set_rate_near */ 

int dir;          /* exact_rate == rate --> dir = 0 */
              /* exact_rate < rate  --> dir = -1 */
              /* exact_rate > rate  --> dir = 1 */
int periods = 2;       /* Number of periods */
snd_pcm_uframes_t periodsize = 8192; /* Periodsize (bytes) */

int num_frames;

/* Set access type. This can be either    */
/* SND_PCM_ACCESS_RW_INTERLEAVED or       */
/* SND_PCM_ACCESS_RW_NONINTERLEAVED.      */
/* There are also access types for MMAPed */
/* access, but this is beyond the scope   */
/* of this introduction.                  */
if (snd_pcm_hw_params_set_access(pcm_handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED) < 0) {
  fprintf(stderr, "Error setting access.\n");
  return(-1);
}
  
/* Set sample format */
if (snd_pcm_hw_params_set_format(pcm_handle, hwparams, SND_PCM_FORMAT_S16_LE) < 0) {
  fprintf(stderr, "Error setting format.\n");
  return(-1);
}

/* Set sample rate. If the exact rate is not supported */
/* by the hardware, use nearest possible rate.         */ 
exact_rate = rate;
if (snd_pcm_hw_params_set_rate_near(pcm_handle, hwparams, &exact_rate, 0) < 0) {
  fprintf(stderr, "Error setting rate.\n");
  return(-1);
}
if (rate != exact_rate) {
  fprintf(stderr, "The rate %d Hz is not supported by your hardware.\n ==> Using %d Hz instead.\n", rate, exact_rate);
}

/* Set number of channels */
if (snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2) < 0) {
  fprintf(stderr, "Error setting channels.\n");
  return(-1);
}

/* Set number of periods. Periods used to be called fragments. */ 
if (snd_pcm_hw_params_set_periods(pcm_handle, hwparams, periods, 0) < 0) {
  fprintf(stderr, "Error setting periods.\n");
  return(-1);
}
  
/* Set buffer size (in frames). The resulting latency is given by */
/* latency = periodsize * periods / (rate * bytes_per_frame)     */
if (snd_pcm_hw_params_set_buffer_size(pcm_handle, hwparams, (periodsize * periods)>>2) < 0) {
  fprintf(stderr, "Error setting buffersize.\n");
  return(-1);
}
  
/* Apply HW parameter settings to */
/* PCM device and prepare device  */
if (snd_pcm_hw_params(pcm_handle, hwparams) < 0) {
  fprintf(stderr, "Error setting HW params.\n");
  return(-1);
}
  
/* Write num_frames frames from buffer data to    */ 
/* the PCM device pointed to by pcm_handle.       */
/* Returns the number of frames actually written. */
snd_pcm_sframes_t snd_pcm_writei(pcm_handle, data, num_frames);
  
/* Write num_frames frames from buffer data to    */ 
/* the PCM device pointed to by pcm_handle.       */ 
/* Returns the number of frames actually written. */
snd_pcm_sframes_t snd_pcm_writen(pcm_handle, data, num_frames);
  
unsigned char *data;
int pcmreturn, l1, l2;
short s1, s2;
int frames;

data = (unsigned char *)malloc(periodsize);
frames = periodsize >> 2;
for(l1 = 0; l1 < 100; l1++) {
  for(l2 = 0; l2 < num_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 ((pcmreturn = snd_pcm_writei(pcm_handle, data, frames)) < 0) {
    snd_pcm_prepare(pcm_handle);
    fprintf(stderr, "<<<<<<<<<<<<<<< Buffer Underrun >>>>>>>>>>>>>>>\n");
  }
}
  
/* Stop PCM device and drop pending frames */
snd_pcm_drop(pcm_handle);

/* Stop PCM device after pending frames have been played */ 
snd_pcm_drain(pcm_handle);

}