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

[tapas <tapas@affenbande.org>]

On Thu, 16 Dec 2004 10:18:12 +0100
Ingo Molnar <mingo@elte.hu> wrote:

> > is
> > 
> > snd_pcm_get_trigger_tstamp()
> > 
> > the api call to get the timestamp of the irq handler?
> > 
> > flo
> 
> in case you want to add it to ALSA within the -RT patchset, -RT now has
> a generic function:
> 
>  extern cycles_t irq_timestamp(unsigned int irq);
> 
> the timestamps do get generated for every irq.
> 
> (but ... the usual disclaimer: this is just a playground thing, so
> there's no guarantee of upstream merging.)

understood.

But the question of using a different timestamp source is still open in
case of the TSC's frequency not being constant. But i suppose this
question can wait until i figured out how to actually get the timestamp
from ALSA.

It looks like snd_pcm_get_trigger_tstamp() is the right call. And its
implementation would have to be adopted to use RP's
irq_timestamp(unsigned int irq)..

Fons Adriaenssen wrote to me that he tried snd_pcm_get_trigger_tstamp(),
but he always got the same value back. Since the docs are rather sparse
i want to ask the alsa-devs about exactly how to use the
snd_pcm_get_trigger_tstamp() call.

Any takers?

Flo


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