seberoon wrote:
> I've done a bit of analysis by hand and found something that may be
> relevant. My expectation was that, for a given player, while a track is
> playing, and assuming no skip aheads, the value of (jiffies -
> elapsed_milliseconds) should remain pretty much constant from one status
> packet to the next. In the attached extract from the log, this is true
> for player A (b8:27:eb:83:7f:a2) but not for player B
> (00:13:ef:20:2d:21). For A that difference is constant at 330081211. For
> B it seems to be oscillating; it starts at 218944165 then goes up and
> down (the offsets from the initial value of 218944165 are 0, +23, +32,
> -1, 0, +23, +32, -1). Would you expect variation on that scale?
It looks to me as though there is a problem in the code which measures
the output delay, towards the end of output_thread() in output_alsa.c.
The call to snd_pcm_delay() is happening before new frames are written
to the device. But insofar as I understand it (not very, as already
demonstrated) writing new frames will increase the output delay, so we
need to measure the delay immediately -after- the call to
_output_frames(). I've tried modifying the code as shown below. Initial
testing indicates that this works but I haven't tested it in anger, nor
have I tried to test if it actually impacts on my original sync issues.
I'd appreciate a heads-up if you can see that I'm heading down a blind
alley.
Code:
--------------------
// check for errors
snd_pcm_sframes_t delay;
if ((err = snd_pcm_delay(pcmp, &delay)) < 0) {
if (err == -EPIPE) {
// EPIPE indicates underrun - attempt to recover
UNLOCK;
continue;
} else if (err == -EIO) {
// EIO can occur with non existant pulse server
UNLOCK;
LOG_SDEBUG("snd_pcm_delay returns: EIO - sleeping");
usleep(100000);
continue;
} else {
LOG_DEBUG("snd_pcm_delay returns: %d", err);
}
}
// process frames
frames_t wrote = _output_frames(avail);
// measure output delay
if ((err = snd_pcm_delay(pcmp, &delay)) < 0) {
LOG_DEBUG("snd_pcm_delay returns: %d", err);
} else {
output.device_frames = delay;
output.updated = gettime_ms();
}
--------------------
------------------------------------------------------------------------
seberoon's Profile: http://forums.slimdevices.com/member.php?userid=63052
View this thread: http://forums.slimdevices.com/showthread.php?t=97046
_______________________________________________
unix mailing list
unix@lists.slimdevices.com
http://lists.slimdevices.com/mailman/listinfo/unix
