[alsa-devel] timestamp update when no hw delta

[Takashi Iwai]

On Tue, 10 Oct 2017 14:14:59 +0200,
Henrik Eriksson wrote:
> 
> Hi
> 
> I am looking into commit 3179f62001880e588e229db3006a59ad87b7792a
> ("ALSA: core: add .get_time_info"), which, if I understand the code
> correctly, changed the behaviour of timestamps.  Before this change,
> snd_pcm_update_hw_ptr0() just returned if the no_delta_check showed that
> the hw_ptr had not changed.  With this change it will update the
> timestamps before returning.
> 
> Was this intended, and if so does anyone have any insights to why?  The
> original behaviour to not update the timestamps when the hw position has
> not changed seems more correct to me, but I am new to this code.

Pierre is the best person to answer this, but AFAIK, the intention is
to allow more fine-grained timestamp, and it's finer than the sample
rate.  That is, you want to know the continuous (wallclock) time stamp
even between two PCM pulses, which allows more exact synchronization
of the PCM timeline and the system/network timeline.


thanks,

Takashi