Re: [Alsa-devel] Re: irq handler top half timestamps

[Lee Revell <rlrevell@joe-job.com>]

On Sat, 2004-12-11 at 01:56 +0100, Florian Schmidt wrote:
> On Fri, 10 Dec 2004 16:01:48 -0500 Lee Revell <rlrevell@joe-job.com> wrote:
> > I don't really consider this new level very significant in practice
> > because it's fast and exactly the same for all devices.  IOW the
> > snd_pcm_period_elapsed timestamp should be good.  I don't think we need
> > to worry about the threaded ALSA IRQ case.
> 
> When exactly is snd_pcm_period_elapsed called? Is it called from the
> ALSA driver interrupt handler (excuse, if this question is stupid, i'm
> not too well versed (mildly speaking) when it comes to driver hacking)?
> Is it the first thing in the irq handling routine?

If the device supports interrupts at the period boundary like most sound
cards it's the only thing in the ALSA interrupt handler:

static void snd_emu10k1_pcm_efx_interrupt(emu10k1_t *emu, unsigned int status)
{
        snd_pcm_period_elapsed(emu->pcm_capture_efx_substream);
}

If the device uses a timer to generate interrupts at a fixed frequency
then you have to manually compare the frames processed to the period
size and call snd_pcm_period_elapsed if the period has indeed elapsed.

Lee




-------------------------------------------------------
SF email is sponsored by - The IT Product Guide
Read honest & candid reviews on hundreds of IT Products from real users.
Discover which products truly live up to the hype. Start reading now. 
http://productguide.itmanagersjournal.com/