Re: [alsa-devel] SEGFAULT : snd_pcm_mmap_begin/commit

Thanks for your observation.

Well, the only pointer dereference is to area, so area has an invalid pointer. Please check the return value of snd_pcm_mmap_begin to see why.

Return value is negative. (-77). How do i resolve it (Using Sleep ?? / snd_pcm_wait() ??)

Hmm, I've haven't used snd_pcm_mmap_* in a long time, but shouldn't the memcpy be above snd_pcm_mmap_commit? Second, if you're using memcpy, why don't settle with snd_pcm_writei in the first place?

i am actually unable to use _commit properly so was judt experimenting using memcpy(). My requirement is to use _begin and _commit.

I will experiment by using memcpy above _commit.

Thanks

________________________________________ From: David Henningsson [david.henningsson@canonical.com] Sent: Tuesday, November 16, 2010 2:29 PM To: Irfan Shaikh Cc: alsa-devel@alsa-project.org Subject: Re: [alsa-devel] SEGFAULT : snd_pcm_mmap_begin/commit

On 2010-11-16 09:44, Irfan Shaikh wrote:

Hello All,

I have been facing dificulty in using snd_pcm_mmap_begin and snd_pcm_mmap_commit. Shows Seg fault as pointed by comment in code below. Please tell me what wrong i am doing and how do i correct.

/###################################################################################/ unsigned int count = (alsaParams->frames/(((alsaParams->bit_per_sample)*(alsaParams->num_channel)) / 8)); unsigned char *data = alsaParams->data;https://owa.sasken.com/owa/?ae=Item&t=IPM.Note&a=New# snd_pcm_sframes_t frames_available, frames_transmit; const snd_pcm_channel_area_t *area; snd_pcm_uframes_t offset; char *outbuffer; int result;

     /*available space in audio-buffer to write to*/
     frames_available = snd_pcm_avail_update(alsaParams->pcm_handle);

     /*
      * prepare the areas
      * and get back area, offset and frames_transmit
      * frames_transmit gives back the REAL value of available frames which could be written to in the mmaped-area
      * frames_transmit are less than frames_available
      */
     frames_transmit = frames_available;

     snd_pcm_mmap_begin(alsaParams->pcm_handle,&area,&offset,&frames_transmit);

     /*calculates the mmaped-buffer which could be written to*/
     outbuffer = ((char *) area->addr + (area->first + area->step * offset)/ 8);    // ****** SEGFAULT *******

Well, the only pointer dereference is to area, so area has an invalid pointer. Please check the return value of snd_pcm_mmap_begin to see why.

     /*gives back the virtually written (writable) frames which should be always == frames_transmit*/
     result = snd_pcm_mmap_commit(alsaParams->pcm_handle, offset, frames_transmit);

     memcpy(outbuffer, data, count);  //data is actual data

Hmm, I've haven't used snd_pcm_mmap_* in a long time, but shouldn't the memcpy be above snd_pcm_mmap_commit? Second, if you're using memcpy, why don't settle with snd_pcm_writei in the first place?

-- David Henningsson, Canonical Ltd. http://launchpad.net/~diwic

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