[alsa-devel] POSIX clocks and ALSA

Takashi Iwai tiwai at suse.de
Mon Nov 26 09:06:43 CET 2007

At Mon, 26 Nov 2007 09:59:29 +0200,
Heikki Lindholm wrote:
> Jaroslav Kysela kirjoitti:
> > On Mon, 26 Nov 2007, Heikki Lindholm wrote:
> > 
> >> Hello,
> >>
> >> Some years ago there was some talk about UST support in Linux, but the 
> >> support never happened. With the hrtimers patch (and I'm not quite sure 
> >> if even earlier?) CLOCK_MONOTONIC would seem like a fairly good UST time 
> >> source. What I'd like to see, is a selectable clock for ALSA 
> >> timestamping, e.g. something like snd_sw_params_clock(..., clockid_t 
> >> clk). Would this seem plausible? I don't know that much about ALSA 
> >> internals, so, no idea whether different clocks on different 
> >> pcms/whatever would quickly turn into an unmanageable mess.
> > 
> > We are aware about this extension and I already proposed an 
> > implementation. I hope to implement it soon. Timestamps are not used in 
> > driver internally.
> I can't seem to google up the proposal. I'd like to read it; was it on 
> the alsa ml?

Yes, it was on alsa-devel ML.  At that time I didn't like the proposal
much because currently there was no real user of timestamps.

The addition of monolithc clock isn't hard, but it's an API change
that involves with the kernel-side change.  So let's do it carefully.

But, honestly, I'm still concerned what to be done first.  Shouldn't
we discuss about the usefulness of the timestamp at first?  That is,
whether the current form (API, implementation) is the best or not,
what kind of user would be, and how it's used.  So far, this feature
is "simply there"...



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