12 Apr
2013
12 Apr
'13
3:17 a.m.
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? -Pierre