Re: [Alsa-devel] Re: [linux-audio-dev] minimum tick time

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Subject: Re: [Alsa-devel] Re: [linux-audio-dev] minimum tick time
From: Takashi Iwai (tiwai_AT_suse.de)
Date: Tue Nov 06 2001 - 20:18:33 EET


At Tue, 06 Nov 2001 19:10:20 +0100,
Abramo wrote:
>
> Takashi Iwai wrote:
> >
> > Hi Maarten,
> >
> > At Tue, 6 Nov 2001 17:12:01 +0100,
> > Maarten de Boer wrote:
> > >
> > > Hello,
> > >
> > > I am trying to get low latency with alsa.
> > > I have kernel 2.4.13 with the preemptive patch and the
> > > alsa-driver/utils/patches/rtc-2.4.9.dif patch applied.
> > > In the kernel configuration, I turned on RTC and
> > > Preemptive.
> > >
> > > I run the alsa-lib/test/latency.c test in poll mode,
> > > but the problem is the tick time, which is at 100 Hz:
> > >
> > > snd_pcm_hw_params_get_tick_time(params, NULL) = 10000
> > >
> > > What am I doing wrong?
> >
> > The timer invoked by pcm is only system timer, so resolution is fixed
> > as HZ. IMO, it would be nice to make it available to use other timer
> > sources, but this will lead to major rewrite..
>
> This would not imply a "major" rewrite: the API and the kernel code has
> been thought for that.
> You need simply to have different snd_pcm_tick_set functions (see
> pcm_lib.c).

Yes, of course, I meant "not so quick and little" hack in kernel
code :) Hmm, perhaps i'm wrong, we can change the code without too
much rewrite.. Let me see..

Anyway, if we use ALSA timer on pcm, we'll need an additional API call
(or module parameter) for timer selection such as given in sequencer
API.

Takashi


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