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

["Martijn Sipkema" <martijn@entmoot.nl>]

[...]
> > 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.

(sorry, a bit off-topic)
Does that mean that ALSA will always have a large (relative to the interrupt
frequency) scheduling jitter for cards that interrupt at a fixed frequency?
Or is it possible to have ALSA return samples immediately after they become
available?


--ms



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