Re: full/half duplex support

[Takashi Iwai <tiwai@suse.de>]

At 19 Nov 2004 21:29:31 +0100,
Luuk van Dijk wrote:
> 
> On Fri, 2004-11-19 at 13:13, Takashi Iwai wrote:
> 
> > Hmm, I don't understand your proposal here.
> > 
> > AFAIUC, the problem is that the trigger callback is called twice, for
> > playback and capture, on the full-duplex mode.  Basically ALSA assumes
> > that the playback and the capture streams are accessible
> > independently, so no such restriction is implemented (yet).
> 
> no it looks like the callback is called multiple times for the second
> stream that is started.   so: hwparams() and prepare() and trigger() for
> the first, say the capture substream works fine.  then I start the
> playback substream.  my prepare() knows to reconfig the dma when either
> channel is running, so that goes well too, and the trigger() knows that
> if either substream is running it doesn't need to start the dma i/o, but
> then the mid-layer queries the current dma pointer for the capture
> stream with the pointer() callback, and I think it doesn't like the
> answer (my interpretation), because I see that it calls trigger() again
> and again.

Then something wrong in the callback routines.  Perhaps the pointer
callback doesn't return the proper expected position, and the core or
the application tries to stop/restart the stream.

The trigger(START) callback is called only in the three places.
One is the SND_PCM_START ioctl, one in the write, and one in the
read to start the stream.  In any cases, the current status is checked
before the callback is called.  So, the fact that the trigger callback
is called many times implies that the PCM state remains PREPARED even
after the first call.


Takashi


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