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.)
-- Heikki Lindholm