On 3/04/2007, at 4:17 AM, David A. De Graaf wrote:
>> Rob Dege wrote:
>>> Last night, while my system was recording a show, a message appeared
>>> in the logs:
>>>
>>> ivtv2 warning: CX2341X_ENC_MISC took 33 jiffies (250 per HZ)
>
>
> Rob, thank you for noticing this clueful error message. I'm pretty
> sure
> it's a direct indication of the problem I described two weeks ago in
> "ivtv vs. system clock" - while recording, the system clock runs
> slowly.
[snip]
> Some kernel operations must ensure atomicity - once begun, they must
> finish without being interrupted. Kernel code can suspend interrupts
> to ensure this, but the suspense must be guaranteed never to exceed a
> critical interval. I think this must be less than 1 jiffy to keep the
> clock accurate, and according to the Wikipedia article, this is either
> 10, 1, or 4 ms, depending on the vintage of the kernel.
>
> I strongly suspect that the ivtv code violates this precept.
Yes, while debugging the mplayer application last night ("mplayer
pvr://" fails to work on my system) I noticed these jiffy messages
(amongst others since mplayer can take out the ivtv driver - but I'll
put that in another report). On my system - a compaq Alpha - the
jiffy appears to be 1ms (1024 per Hz in the warning message) and I
get warnings of misses of almost up to 200 jiffies. No wonder my
clock can slow down considerably. I'm running ivtv 0.10.0.
After patching my copy of mplayer last night so at least it can read
data from the pvr:// device (a PVR-350) I also noticed that it
doesn't read data from the ivtv quickly enough so that the ivtv
internal buffers eventually overflow. I wonder if this might also be
tied up with the slow clock, so that mplayer is trying to play back
the MPEG stream at a slightly slow rate and thus is getting out of
sync with the driver. This also occurs if I run "mplayer /dev/
video0" as well as "mplayer pvr://".
I seem to recall Hans saying recently (was it last week?) on this
forum that he has a fix for the slow clock problem in the works. I
guess we have to sit tight and wait for that.
Cheerz
Michael.
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