[alsa-devel] my driver can't reproduce continuously

[Takashi Iwai]

At Mon, 27 Jul 2009 16:43:05 +0900,
Kuninori Morimoto wrote:
> 
> 
> Dear Takashi
> 
> Thank you for your comment
> 
> > > when 1st buffer was send,
> > > driver stop.
> > > 2nd trigger function isn't called.
> > 
> > Check the raw value returned from the pointer callback, too.
> > This can be the real cause.
> 
> I might have been doing a very big misunderstanding.
> 
> > The pointer callback is supposed to give the currently played position
> > offset in a ring buffer, and ranged from 0 to buffer_size-1.
> 
> Does this "ring buffer" mean
> I should transmit runtime->dma_area many times 
> from offset 0x0 ??

Yes and no.  A ring buffer may contain multiple "periods" (or
"fragments") in it.  In your case, a ring buffer has 4 periods.
Until these 4 periods are sent out, the offset goes incrementally.
Once it reaches to buffer_size, it returns to zero again.

> => when I call 4th elapsed,
>    should I send runtime->dma_area + 0x0 again ?

Yes.


> If so,
> my driver get STOP on trigger funtion many times
> even if I didn't stop it.
> 
> START
> STOP
> underrun!!!
> START
> STOP
> underrun!!!
> ...
> 
> Does this correct operation ?

Yes, because the PCM core thinks a buffer underrun happens,
judging from the pointer callback value your driver returned.
That's why I asked many times to check the values returned from the
pointer callback.  This value and the timing of
snd_pcm_period_elapsed() is the only information the PCM core checks.


Takashi