[alsa-devel] Re: Timestamping

New Message Reply About this list Date view Thread view Subject view Author view Other groups

Subject: [alsa-devel] Re: Timestamping
From: Paul Barton-Davis (pbd_AT_op.net)
Date: to loka   28 1999 - 09:21:31 EDT


>I'm one of the guys working on the V4L2 project
>http://millennium.diads.com/bdirks/v4l2.htm. Kernel timestamping is
>a core feature of V4L2 and referencing a global system clock turned
>out most flexible. But it has been argued system time as returned by
>the gettimeofday function is not guaranteed to increase monotonically.
>
>Since we want to do the right thing(TM) we consider an implementation
>similar to SGI's Unadjusted System Time clock, see
>http://millennium.diads.com/mschimek/ust for a brief discussion.
>
>What do you think about UST support for ALSA?

what do *i* think ? from reading the IRIX documentation, it makes me
want to go out, dump my Linux kernel, and run IRIX forever more.

the sooner we have the kind of support that is described in the SGI
documentation, the better. anyone with any experience working with
audio and/or video knows that this stuff is critical for professional
results, and i suspect that its the kind of thing that continues to
make SGI a darling of the video editing world.

everyone on linux-audio-dev should read the SGI docs referenced at

         http://millennium.diads.com/mschimek/ust

i am a little sceptical of SGI's implementation, however - its not
clear whether they are doing kernel/driver timestamping or
inferencing. also, the fact that you cannot use read(2)/write(2)
anymore is always a negative from my perspective, but hey, alsa-lib
challenges that model already. i will just be sad to have to abandon
read/write for MIDI in order to get timestamps, but i see no other way
of doing it.

i am very intrigued by their description of when the timestamp is done
for audio. they claim to timestamp analog data at "the instant the
voltage is sampled or produced" and digital data at the "edge of the
recovered sample clock from the input signal or the driving sample
clock for the output signal".

do we have any hope of doing this ? does SGI ? :)

--p
------
To unsubscribe from <alsa-devel_AT_alsa-project.org> mailing list send message
'unsubscribe' in the body of message to <alsa-devel-request_AT_alsa-project.org>.
BUG/SMALL PATCH REPORTING SYSTEM: http://www.alsa-project.org/cgi-bin/bugs


New Message Reply About this list Date view Thread view Subject view Author view Other groups

This archive was generated by hypermail 2b28 : pe maalis 10 2000 - 07:28:00 EST