[alsa-devel] [PATCH 0/2] RFC: support for audio wall clock

[Takashi Iwai]

At Thu, 28 Jun 2012 16:12:33 -0500,
Pierre-Louis Bossart wrote:
> 
> V2 of patches to show how the audio wall clock (eg. the
> HDAudio one) can be used to provide precise audio timestamps and track
> the drift between audio time and system time. On my laptop I am able
> to track a 7ppm delta.  
> I will explain in more details how this can be
> used during LPC in San Diego, but with the summer coming I'd like to
> get feedback as there are changes to the core/alsa-lib that haven't
> been modified in years.

Sorry for the late reply.  I've looked over the things around my
vacation...

This version looks better, so if other people have no objection, I can
merge it.  The extension of mmap_status seems still fitting with 64bit
char size, so it should be OK.

But, one thing -- can't we reuse the normal tstamp field for the audio
wallclock?  That is, add a new tstamp mode, and then put wallclock
tstamp there instead of the normal system tstamp.  Just an idea.


thanks,

Takashi

> 
> TODO:
> - 64-bit alignment, verification of pcm_compat.c changes
> - handling of digital inputs, need to disable wall-clock timestamps in that case (feedback from Clemens)
> - check differences in protocol
> - change timecounter to avoid accumulation of rounding errors in cycle->ns conversions
> - check overflows
> - rework the timecounter init on trigger
> 
> Pierre-Louis Bossart (2):
>   ALSA: core: add hooks for audio timestamps read from WALLCLOCK
>   ALSA: hda: support for wallclock timestamps
> 
>  include/sound/asound.h    |    7 ++++-
>  include/sound/pcm.h       |    2 +
>  sound/core/pcm_compat.c   |   13 +++++++++-
>  sound/core/pcm_lib.c      |   15 ++++++++++-
>  sound/core/pcm_native.c   |    2 +
>  sound/pci/hda/hda_intel.c |   54 ++++++++++++++++++++++++++++++++++++++++++++-
>  6 files changed, 86 insertions(+), 7 deletions(-)
> 
> -- 
> 1.7.6.5
> 
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