Alsa asynchonus playnback

Alsa asynchonus playnback

[Martin schmidt]

Hello,

I want to play audiodata using alsa and do as it is explained in
http://alsa.opensrc.org/Asynchronous_Playback_%28Howto%29
http://equalarea.com/paul/alsa-audio.html#interruptex
1. open device
2 define a callback

void MyCallback(snd_async_handler_t *pcm_callback)   { ...  }


      err = snd_async_add_pcm_handler(&pcm_callback, pcm_handle,
MyCallback, NULL);
      if(err<0){
          fprintf (stderr, "err = %d --> snd_async_add_pcm_handler:
(%s)\n",err,snd_strerror (err));
      }

return -38 ( function is not implemented )???

i a loop I generate the audiodata

void produce_audiodata(short* left, short *right)
{

 for(int k = 0; k< max;k++){
  audio[2*k]= left[k];
  audio[2*k+1]= right[k];
  }
   Mycallback(...)  is it the right place to call it ?
}

thanks

Re: Alsa asynchonus playnback

[Clemens Ladisch]

Martin schmidt wrote:
> I want to play audiodata using alsa and do as it is explained in
> http://alsa.opensrc.org/Asynchronous_Playback_%28Howto%29
> http://equalarea.com/paul/alsa-audio.html#interruptex

These links describe two different mechanisms.

> return -38 ( function is not implemented )???

This is one of the reasons why you shouldn't use async notifications.

Is there a reason why you do want to use them?


Regards,
Clemens

Re: Alsa asynchonus playnback

[Clemens Ladisch]

Martin schmidt wrote:
> my problem is, the sound has an Echo (in german Hall-Effekt).
>
> int write_to_audiostream(short*buf)
> {
>     memcpy(audiobuffer[audiobuffercounter],buf,audio_buffersize*sizeof(short));
>    int w=  snd_pcm_writei (pcm_handle, audiobuffer[audiobuffercounter], 2* audio_buffersize);

This looks correct (as long as the buffer is correctly filled).
Do you ever check w?

>    audiobuffercounter = ++audiobuffercounter % 10;

It is a bad idea to disable compiler warnings, or to not heed them.

> in a Timer-Event

Why a timer?  How is the timer synchronized to the sample clock?


Regards,
Clemens