[alsa-devel] Latency and timestamps

[Takashi Iwai]

At Wed, 21 Nov 2007 13:33:59 +0200,
Heikki Lindholm wrote:
> 
> Takashi Iwai kirjoitti:
> > At Mon, 19 Nov 2007 22:46:31 -0200,
> > Claudio Matsuoka wrote:
> >> Hi,
> >>
> >> I'm adding latency control to an application and didn't find much
> >> documentation about the pcm status functions aside from a very brief
> >> description and the latency.c example. What exactly are the "trigger
> >> timestamp" and "now timestamp" returned by
> >> snd_pcm_status_get_trigger_tstamp() and snd_pcm_status_get_tstamp()?
> > 
> > The trigger_tstamp is the time-stamp at the last time the PCM status
> > change occured.  For example, when the PCM is really triggered to
> > start, or stopped, or XRUN, etc.  It won't be changed as long as the 
> > PCM status is kept.
> > 
> > OTOH, the tstamp is the current timestamp (now).  But, this value has
> > a slightly different meaning when tstamp_mode is set to
> > SND_PCM_TSTAMP_MMAP.  Then it keeps the timestamp of the last period
> > update time instead of the now.
> 
> Good explanation. How about adding this to the API documentation, too? 
> Even a copy-paste of the above would be much much better than what's in 
> there now (basically repetitions of the already quite verbose function 
> names.)

As usual, a patch is always welcome ;)


Takashi