基于alsa驱动架构的pcm播放

/*modify by hfl 2014-2-16*/

/* Use the newer ALSA API */
#define ALSA_PCM_NEW_HW_PARAMS_API


#include <alsa/asoundlib.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
  long loops;
  int rc;
  int size;
  snd_pcm_t *handle;
  snd_pcm_hw_params_t *params;
  unsigned int val;
  int dir;
  snd_pcm_uframes_t frames;
  printf("222133\n");
 char buffer[20*2];/*size=frame*channles*byte persaple*/
 int fd,i;
if (argc != 2)
{
fprintf (stderr, "usage: %s <filename>!\n", argv[0]);
exit ( -1 ) ;
}


if ( ( fd = open (argv[1],O_RDONLY))<0)
{
fprintf ( stderr, " Can't open sound file!\n");
exit (-1 );
}
  /* Open PCM device for playback. */
  rc = snd_pcm_open(&handle, "default",
                    SND_PCM_STREAM_PLAYBACK, 0);
  if (rc < 0) {
    fprintf(stderr,
            "unable to open pcm device: %s\n",
            snd_strerror(rc));
    exit(1);
  }




  /* Allocate a hardware parameters object. */
  snd_pcm_hw_params_alloca(&params);


  /* Fill it in with default values. */
  snd_pcm_hw_params_any(handle, params);


  /* Set the desired hardware parameters. */


  /* Interleaved mode */
  snd_pcm_hw_params_set_access(handle, params,
                      SND_PCM_ACCESS_RW_INTERLEAVED);


  /* Signed 16-bit little-endian format */
  snd_pcm_hw_params_set_format(handle, params,
                              SND_PCM_FORMAT_S16_LE);


  /* Two channels (stereo) */
  snd_pcm_hw_params_set_channels(handle, params, 1);


  /* 44100 bits/second sampling rate (CD quality) */
  val = 16000;
  snd_pcm_hw_params_set_rate_near(handle, params,
                                  &val, &dir);


  /* Set period size to 32 frames. */
  frames =20;/*一次送人的帧太少，会下溢冲（至少15帧)*/
 // snd_pcm_hw_params_set_period_size_near(handle,  params, &frames, &dir);


  /* Write the parameters to the driver */
  rc = snd_pcm_hw_params(handle, params);
  if (rc < 0) {
    fprintf(stderr,
            "unable to set hw parameters: %s\n",
            snd_strerror(rc));
    exit(1);
  }


  /* Use a buffer large enough to hold one period */
 
 // snd_pcm_hw_params_get_period_size(params, &frames,&dir);
  //size = frames * 4; /* 2 bytes/sample, 2 channels */
 // buffer = (char *) malloc(size);


long s=0;
 i =0;
  while(i = read(fd,buffer, sizeof(buffer))>0)
  {
  //s+=i;
  //printf("s=%ld\n",s);
    #if 0
    rc = read(0, buffer, size);
    if (rc == 0) {
      fprintf(stderr, "end of file on input\n");
      break;
    } else if (rc != size) {
      fprintf(stderr,
              "short read: read %d bytes\n", rc);
    }
#endif
     rc = snd_pcm_writei(handle, buffer, frames);
    if (rc==frames*2)
    {
     printf("read data oK\n");
    }
    if (rc == -EPIPE) {
      /* EPIPE means underrun */
      fprintf(stderr, "underrun occurred\n");
      snd_pcm_prepare(handle);
    } else if (rc < 0) {
      fprintf(stderr,
              "error from writei: %s\n",
              snd_strerror(rc));
    }  else if (rc != (int)frames) {
      fprintf(stderr,
              "short write, write %d frames\n", rc);
    }
  }
  snd_pcm_drain(handle);
  snd_pcm_close(handle);
  printf("play end \n");
//  free(buffer);
  close(fd);
  return 0;

}

因为alsa 架构开放给用户的接口不是直接操作驱动，而是操作一个库的接口，相当于在驱动的上层做了一层封装的SDK。因此编译是要链接到一个动态库，并包含相应的头文件。注意alsa架构送数据是以frame为单位送的。size=frames*channel*每个采样的字节数。frame不能太小，否则会产生下溢，造成卡顿。在读文件的环境当中，frame至少15以上。

编译命令：

gcc -o pcmplayalsa pcmplayalsa.c -I/usr/include/alsa -lasound