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

[Takashi Iwai]

At Thu, 11 Apr 2013 19:17:10 -0600,
Pierre-Louis Bossart wrote:
> 
> 
> >> 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?
> 
> you now have 3 positions:
> 
> For capture:
> hwptr = sample in memory
> hwptr+ delay = sample recorded on link (tracked by LPIB and wallclock)
> hwptr+ delay + codec_delay = sample recorded by A/D
> 
> For playback
> hwptr = next sample in memory to be DMA'ed
> hwptr - delay = sample pushed on link (tracked by LPIB and wallclock)
> hwptr - delay - codec_delay = sample played in A/D
> 
> the wallclock is only at the soc/chipset level, it doesn't know anything 
> about the peripheral.
> Makes sense?

Thanks, now it's clearer.


Takashi