[alsa-devel] POSIX clocks and ALSA

Heikki Lindholm holindho at cs.helsinki.fi
Mon Nov 26 11:10:51 CET 2007

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.

-- Heikki Lindholm

More information about the Alsa-devel mailing list