On Mon, 26 Nov 2007, Takashi Iwai wrote: > 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. I cannot find it quickly, but you may check alsa-devel archives. > 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"... The precise timestamps are necessary to keep in sync multiple timing sources. First example if you have multiple cards with different clocks, a code maintaining drifts using an adaptive resampler might be created. We need definitely one master time source. And I think that it is best, if this master timer source can be shared with other unix applications as well (video, scheduling real-time events etc.). So, logically, in my opinion, the best master timer source is the system clock. Jaroslav ----- Jaroslav Kysela <perex@xxxxxxxx> Linux Kernel Sound Maintainer ALSA Project _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
