[alsa-devel] [PATCH] pcm_lib.c: Fixed inaccurate calculation of hw_ptr_interrupt in snd_pcm_update_hw_ptr_interrupt function

[Takashi Iwai]

At Wed, 19 Aug 2009 12:48:26 +0000,
Shine Liu wrote:
> 
> On Wed, 2009-08-19 at 14:05 +0200, Takashi Iwai wrote:
> > > 
> > > But the irq last issued should be at 0x3e80, but not 0x3800 + 0x800 =
> > > 0x4000. The DMA engine loaded 0x680 frame not 0x800 frame at the last
> > > time.
> > 
> > Then it's a driver bug.  If unaligned period size is allowed, it means
> > that the irq is really generated in that period, not at the buffer
> > boundary.  Otherwise, it must have a proper hw-constraint to align the
> > period size to the buffer size.
> > 
> > What hardware is it?
> 
> Yes, but there's no constraint code currently to force to align the
> period size to the buffer size. The bug occurs on linux-2.6.31-rc6 on
> ASoC s3c24xx platform.
> 
> The constraint to force to align the period size to the buffer size
> should not be hardware depended, it shoud be done in the generic layer,
> is it?

It is hardware dependent, i.e. how the irq is generated.
If the irq is generated in a way like timer, the period size doesn't
have to be aligned with the buffer size.  But your case doesn't look
like that.


Takashi