[alsa-devel] Latency and timestamps

Heikki Lindholm holindho at cs.helsinki.fi
Wed Nov 21 12:33:59 CET 2007

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 

-- Heikki Lindholm

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