[alsa-devel] POSIX clocks and ALSA

[Takashi Iwai]

At Mon, 26 Nov 2007 12:10:51 +0200,
Heikki Lindholm wrote:
> 
> Takashi Iwai kirjoitti:
> > 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.
> 
> What do you mean by this? Aren't all applications that try to do 
> playback/capture A/V sync or sync between two audio cards or latency 
> measurement potential users? And those kind of apps have definitely been 
> there before 2007-02 (Jaroslav's RFC's date.) If you mean _monotonic_ 
> timestamps, not all users would probably care, though.

I meant as the apps that really use the ALSA timestamp features.


Takashi