[alsa-devel] [PATCH v2] ALSA: hda - Apply codec delay to wallclock.

[Takashi Iwai]

At Wed, 10 Apr 2013 07:29:32 -0700,
Pierre-Louis Bossart wrote:
> 
> 
> >>
> >>> +       return (nsec > codec_nsecs) ? nsec - codec_nsecs : 0;
> >>
> >>
> >> Is this correct? I would think for capture you need to add the delay, and
> >> subtract it for playback?
> >
> > Should the capture timestamp represents the wall time when the sample
> > is converted by the A-to-D?  If so, would be the correct time be the
> > codec delay nsec before what is reported here?
> 
> For playback audio_timestamp = wallclk - codec_delay_in_nsec
> for capture audio_timestamp = wallclk + codec_delay_in_nsec

Hmm...  I'm confused, too.  From a pretty generic view,

- hwptr = the samples (frames) transferred on the (memory) buffer
- hwptr + PCM delay = the point being currently captured

Which position does the wall clock correspond?


Takashi