I have a single threaded ALSA application which does simultaneous capture and playback. But i am getting overflow error XRUN from capture side.

I am attaching the code to this mail.

Is there any problem with single threaded approach?

Is there any global configuration for ALSA lib?

When i run this app, ALSA state is getting corrupted, even aplay and arecord is not working properly after that.

Any comments on this issue?

Thanks in advance Nobin Mathew

On 5/22/07, Ciaccia ciacciax@yahoo.com wrote:

...

What are the complications in implementing simultaneous playback and capture in ALSA???

I would like to add something to this post: what is the "best" way to program a full duplex application? I would like to have an application that does full-duplex, with the lowest possible latency and using less CPU resource as possible. I tried different approaches, but I was not completely satisfied with none of them....

Here is what I tried: -having two threads, one for playback and one for capture -defining 2 callbacks with async_handles and do all the processing in the callback functions (the last attempt) -using poll() to wait for one of the streams to be ready (see attached file fullduplex.c)

Could some of you look at the attached code (it is not generic and contains lots of asserts, but it's supposed to work only on one single machine) and tell me if the last approach using poll is well structured?

The main loop looks as following:

...

while (1) { err = poll(ufds, 2, -1);

   for (i = 0; i < 2; i++)
   {
       if (snd_pcm_poll_descriptors_revents(handles[i], &ufds[i], 1, &revents) < 0)
       {
           printf("Error getting revents for %s\n", descriptors[i].name);
           exit(1);
       }

       if (revents & descriptors[i].poll_flag)
       {
           if (transfer_loop(handles[i], &first[i], descriptors[i].func) < 0)
           {
               printf("transfer_loop error for %s\n", descriptors[i].name);
               // TODO exit?!?
           }
       }
   }

}

and the transfer_loop is a modified version of the loop found in the ALSA examples (pcm.c and latency.c). Is this strategy optimal in respect to low latency and low CPU usage?

Every comment is greatly appreciated Andrea

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