From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takashi Iwai <tiwai@suse.de>
Subject: Re: hw pause in USB
Date: Tue, 13 Dec 2005 12:14:20 +0100
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	<20051213091651.GA23938@turing.informatik.uni-halle.de>
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To: Clemens Ladisch <ladischc@informatik.uni-halle.de>
Cc: Steve deRosier <derosier@pianodisc.com>, Alsa-Devel <alsa-devel@lists.sourceforge.net>
List-Id: alsa-devel@alsa-project.org

At Tue, 13 Dec 2005 10:16:51 +0100,
Clemens Ladisch wrote:
> 
> Steve deRosier wrote:
> > When running my player via commandline and pressing pause, I get the 
> > following error message out of ALSA lib:
> > 
> > ALSA lib pcm_hw.c:535:(snd_pcm_hw_pause) SNDRV_PCM_IOCTL_PAUSE failed: 
> > Function not implemented
> > 
> > I'm guessing that the USB driver doesn't implement pause.
> 
> Yes.
> 
> > My program implements pause by calling snd_pcm_pause( hPCM, 1 );.
> 
> You cannot call snd_pcm_pause() when the device doesn't support it
> (it should have returned an error code).
> See snd_pcm_hw_params_can_pause().
> 
> > * Is there a better way to implement pause in my client program?  
> 
> snd_pcm_stop()

Heh, it's snd_pcm_drop() in alsa-lib :)

snd_pcm_drop() will stop DMA and abandon the whole data on the ring
buffer.  To restart the stream, you have to call snd_pcm_prepare()
and fill the rest data again (and start with snd_pcm_start() if
necessary).

So, obviously, this procedure isn't "better" than snd_pcm_pause(),
but works with all devices as a fallback.


Takashi


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