Re: [alsa-devel] snd_pcm_mmap_commit

19 Nov 2010


      As per your valuable inputs modified code using snd_pcm_wait
/$$$$ My code waits indefinetly in snd_pcm_wait() $$$$$/
If i set some timer again frames available shows to be zero.
#ifdef DIRECT1
  snd_pcm_state_t state;
  int err, first = 1;
  snd_pcm_sframes_t frames_available, frames_transmit,commitres;
  snd_pcm_uframes_t size, offset;
  unsigned char *outbuffer;
  const snd_pcm_channel_area_t *area;
  static int irf=0;
state = snd_pcm_state(alsaParams->pcm_handle);
  if (state == SND_PCM_STATE_XRUN)
  {
    err=xrun_recovery(alsaParams->pcm_handle, -EPIPE);
    if (err < 0) {
      printf("XRUN recovery failed: %s\n", snd_strerror(err));
      exit(EXIT_FAILURE);
    }
    first = 1;
  }
  else if (state == SND_PCM_STATE_SUSPENDED)
  {
    err = xrun_recovery(alsaParams->pcm_handle, -ESTRPIPE);
    if (err < 0) {
      printf("SUSPEND recovery failed: %s\n", snd_strerror(err));
      exit(EXIT_FAILURE);
    }
  }
   frames_available = snd_pcm_avail_update(alsaParams->pcm_handle);
  if (frames_available < 0) {
    err = xrun_recovery(alsaParams->pcm_handle, frames_available);
    if (err < 0) {
      printf("avail update failed: %s\n", snd_strerror(err));
      exit(EXIT_FAILURE);
    }
    first = 1;
    printf("RETURN : Should Be continued\n");
    return;
  }
  printf("Farames available : %d\n", frames_available);
  if(frames_available<=0)
  {
#if 1
      err = snd_pcm_wait(alsaParams->pcm_handle, -1);    /############ WAIT here indefinitely ##############/
      if (err < 0) {
        if ((err = xrun_recovery(alsaParams->pcm_handle, err)) < 0) {
          printf("snd_pcm_wait error: %s\n", snd_strerror(err));
          exit(EXIT_FAILURE);
        }
      }
#endif
      irf=1;
      return;
  }
  else if(irf==1)
  {
      err = snd_pcm_start(alsaParams->pcm_handle);
      if (err < 0) {
        printf("Start error: %s\n", snd_strerror(err));
        exit(EXIT_FAILURE);
      }
      irf=0;
  }
   size=frames_available;
  while (size > 0) {
    frames_transmit = size;
    err=snd_pcm_mmap_begin(alsaParams->pcm_handle, &area, &offset, &frames_transmit);
    if (err < 0) {
      if ((err = xrun_recovery(alsaParams->pcm_handle, err)) < 0) {
        printf("MMAP begin avail error: %s\n", snd_strerror(err));
        exit(EXIT_FAILURE);
      }
      first = 1;
    }
    printf(">>>>Begin result : %d\n", err);
    outbuffer = ((char *) area->addr + (area->first + area->step * offset)/ 8); //Copies Actual data
commitres = snd_pcm_mmap_commit(alsaParams->pcm_handle, offset, frames_transmit);
    if (commitres < 0 || (snd_pcm_uframes_t)commitres != frames_transmit) {
      if ((err = xrun_recovery(alsaParams->pcm_handle, commitres >= 0 ? -EPIPE : commitres)) < 0) {
        printf("MMAP commit error: %s\n", snd_strerror(err));
        exit(EXIT_FAILURE);
      }
      first = 1;
    }
    printf(">>>>>>>>>>>>>>>>>>>>>>Comit result : %d\n", commitres);
    size -= frames_transmit;
  }
#endif
________________________________________
From: Jaroslav Kysela [perex@perex.cz]
Sent: Friday, November 19, 2010 12:41 PM
To: Irfan Shaikh
Cc: alsa-devel@alsa-project.org
Subject: Re: [alsa-devel] snd_pcm_mmap_commit
On Fri, 19 Nov 2010, Irfan Shaikh wrote:
...
/*************************************************************/
Code below O/p results runs in a while loop till end of PCM data.

First time O/p is
      Farames available : 1024                                                /*Return VALUE of snd_pcm_avail_update*/
      >>>>>>>>>>>>>>>>>>>>>>>>>Begin result : 0      /*Return VALUE of snd_pcm_mmap_begin*/
      Address outbuffer : 0xcff88
      >>>>>>>>>>>>>>>>>>>>>>Comit result : 1024       /*SUCESSFUL - Return VALUE of  snd_pcm_mmap_commi*/

Second time onwards ALWAYS O/p is
      Farames available : 0                                                      /*Return VALUE of snd_pcm_avail_update*/
      >>>>>>>>>>>>>>>>>>>>>>>>>Begin result : 0      /*Return VALUE of snd_pcm_mmap_begin*/
      Address outbuffer : 0xcff88
      >>>>>>>>>>>>>>>>>>>>>>Comit result : 0             /*FAILURE - Return VALUE of  snd_pcm_mmap_commit*/


You have to use poll()/select() or snd_pcm_wait() to wait for a room in
the playback buffer. The direct mmap I/O is always non-blocked.
Jaroslav
-----
Jaroslav Kysela perex@perex.cz
Linux Kernel Sound Maintainer
ALSA Project, Red Hat, Inc.
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