Simple noise generator

player.c

#include <alsa/asoundlib.h>
#include <stdint.h>
#include <stdlib.h>
#include <sched.h>

snd_pcm_t *player_init(char *soundcard, int nbsamples)
{
  int ret;
  snd_pcm_t *playback_handle;

  snd_pcm_open(&playback_handle, soundcard, SND_PCM_STREAM_PLAYBACK, 0);

  snd_pcm_hw_params_t *hw_params;
  snd_pcm_hw_params_malloc(&hw_params);

  snd_pcm_hw_params_any(playback_handle, hw_params);

  int channels = 2;
  snd_pcm_hw_params_set_channels(playback_handle, hw_params, channels);

  snd_pcm_hw_params_set_access(playback_handle, hw_params, SND_PCM_ACCESS_RW_INTERLEAVED);

  snd_pcm_format_t pcm_format = SND_PCM_FORMAT_S16_LE;
  snd_pcm_hw_params_set_format(playback_handle, hw_params, pcm_format);

  unsigned int rate = 44100;
  snd_pcm_hw_params_set_rate_near(playback_handle, hw_params, &rate, NULL);

  int periods = 3;
  ret = snd_pcm_hw_params_set_periods(playback_handle, hw_params, periods, 0);
  if (ret != 0)
    printf("set_periods error %s\n", snd_strerror(ret));
  ret = snd_pcm_hw_params_set_period_size(playback_handle, hw_params, nbsamples, 0);
  if (ret != 0)
    printf("set_period_size error %s\n", snd_strerror(ret));
  ret = snd_pcm_hw_params_set_buffer_size(playback_handle, hw_params, nbsamples * periods);
  if (ret != 0)
    printf("set_buffer_size error %s\n", snd_strerror(ret));

  snd_pcm_hw_params(playback_handle, hw_params);

  snd_pcm_uframes_t buffersize = 0;
  snd_pcm_hw_params_get_buffer_size(hw_params, &buffersize);

  snd_pcm_uframes_t periodsize = 0;
  snd_pcm_hw_params_get_period_size(hw_params, &periodsize, 0);

  snd_pcm_hw_params_get_periods(hw_params, &periods, 0);

  printf("buffersize %ld, periodsize %ld, nb periods %d\n", buffersize, periodsize, periods);

  snd_pcm_prepare(playback_handle);
  snd_pcm_hw_params_free(hw_params);

  return playback_handle;
}

int generator_init(void)
{
  unsigned int seed;
  int fd = open("/dev/random", R_OK);
  sched_yield();
  read(fd, &seed, sizeof(seed));
  close(fd);
  srandom(seed);
}

void generator(int16_t *samples, int nbsamples, int16_t max)
{
  int i;
  for (i = 0; i < nbsamples; i++)
  {
    int16_t *left = &samples[i * 2];
    int16_t *right = &samples[i * 2 + 1];
    *left = random() * max / RAND_MAX;
    *right = random() * max / RAND_MAX;
  }
}

typedef void (*generator_t)(int16_t *samples, int nbsamples, int16_t max);

int player_run(snd_pcm_t *playback_handle, int nbsamples, generator_t generator)
{
  int run = 1;
  int16_t *buffer = malloc(nbsamples * sizeof(int16_t) * 2);
  generator_init();
  while (run)
  {
    generator(buffer, nbsamples, INT16_MAX);
    snd_pcm_writei(playback_handle, buffer, nbsamples);
  }
  free(buffer);
}

void player_finish(snd_pcm_t *handle)
{
  snd_pcm_drain(handle);
  snd_pcm_close(handle);
}

int main(int argc, char **argv)
{
  snd_pcm_t *handle = player_init("default", 1024);
  generator_init();
  player_run(handle, 1024, &generator);
  player_finish(handle);
}