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

[Dylan Reid]

On Mon, Apr 8, 2013 at 9:34 AM, Takashi Iwai <tiwai at suse.de> wrote:
> At Mon, 08 Apr 2013 11:31:12 -0500,
> Pierre-Louis Bossart wrote:
>>
>>
>> > +   if (hinfo->ops.get_delay) {
>> > +           codec_nsec =
>> > +                   hinfo->ops.get_delay(hinfo, codec, substream) * 1000000;
>> > +           if (stream == SNDRV_PCM_STREAM_CAPTURE)
>> > +                   nsec = (nsec > codec_nsec) ? nsec - codec_nsec : 0;
>> > +           else if (stream == SNDRV_PCM_STREAM_PLAYBACK)
>> > +                   nsec += codec_nsec;
>>
>> Can the .get_delay be modified to provide a better resolution than a ms?
>> If you already convert to time, microseconds would seem like a better
>> fit? Your codec seems to report frames (ie 20.83 us).
>
> Actually the patch must be wrong -- get_delay returns the delay in
> frame (sample) unit.

Of course you're right.  That's annoying, it will have to convert from
ms to frames (in get_delay) then to ns here.  Converting from frames
to ns here is a better idea, but for this particular codec, all I have
is ms resolution.

Pierre,
What should the capture timestamp represent?  When the sample hits the
A-to-D or when it is read out of the buffer?

Thanks,

-dg

>
>
> Takashi