[alsa-devel] [PATCH] ALSA: Provide a CLOCK_MONOTONIC_RAW timestamp type

[Takashi Iwai]

At Tue, 08 Jul 2014 21:54:32 +0200,
Jaroslav Kysela wrote:
> 
> Date 8.7.2014 18:00, Mark Brown wrote:
> > On Tue, Jul 08, 2014 at 05:00:26PM +0200, Takashi Iwai wrote:
> >> Mark Brown wrote:
> > 
> >>> due to that. A raw monotonic time which does not include any adjustments
> >>> is available in the kernel from getrawmonotonic() so provide userspace with
> >>> a new timestamp type SNDRV_PCM_TSTAMP_TYPE_MONOTONIC_RAW which provides
> >>> timestamps based on this as an option.
> > 
> >> This looks good to me.  Or, thinking of the original use case, should
> >> we just replace ktime_get_ts() with getrawmonotonic()?  The MONOTONIC
> >> mode is really to be monotonic.
> > 
> > I'm totally OK with that as well if people don't mind that, I just added
> > a new clock as the most conservative option.  I can easily respin the
> > patch for this if you prefer?
> 
> Note that the silent change would break the timestamp compatibility,
> because monotonic timestamp is used in alsa-lib by default. I would
> prefer to add a new type as originaly proposed and allow to choose
> between NTP monotonic and raw monotonic. Also the network timestamp
> might allow better synchronization for network apps (not sure about the
> real usage now, but we're working on an universal framework).

Agreed, it's better to have a separate type, then.
I'm going to take the patch to for-next branch.

> >> While we're at it: there's been long-standing request from V4L guys
> >> for improving the timestamps to sync with video streams.  I suggested
> >> to add a new mode that can be set by the driver.  Worth to consider
> >> it, too?
> > 
> > Does the wall clock stuff address that?  I've no objection to adding a
> > further type if the existing ones (and this one aren't sufficient).
> 
> I'm curious about requested sync, too..

Yeah, the wall clock stuff might work.  But I forgot the detailed
requirement.  Let's see whether it suffices for V4L guys.


thanks,

Takashi