On Wednesday 21 March 2007 20:49, David A. De Graaf wrote:
> There seems to be a bad interaction between ivtv and the system
> clock. After much experimentation, I've found that both ivtv-0.10.0
> and ivtv-0.10.1 have this problem, but ivtv-0.8.1 does not.
>
> When mythtv records TV programs with my Hauppauge WinTV PVR 150, the
> system clock runs slowly - so much that ntpd loses sync. When
> recording ends the system clock resumes normal speed.
>
> Once nptd loses sync, the time error grows so large it won't
> recapture. This messes up the recording schedule, among other things.
>
> To allow ntpd to recapture, it is necessary to make a gross change in
> the kernel clock parameters, tick and frequency, by running the
> command adjtimex -a
>
> After this process deduces and installs new values for tick and
> frequency, restart ntpd
> /etc/init.d/ntpd restart
> This resets the system clock to the server in /etc/ntp/step-tickers
> and ntpd will recapture.
>
> I wrote a simple script to automate this clock resetting process
> whenever the time error exceeds 5 seconds. The data shows a bimodal
> operation with a value of tick of 9998 when not recording, and 10370
> when recording. A value of 10000 is normal, so the 9998 is probably
> normal enough. The value of 10370 while recording means that the
> clock must be given an extra kick of 3.7% at each interrupt. This is
> a rather gross error, and suggests that the recording process is
> somehow causing about 3.7% of the clock interrupts to be missed.
> However this is not a random value; it is quite repeatable.
>
> Comparing the clock resets with the recording history reveals perfect
> correlation. Whenever recording starts, the clock speed needs to
> be boosted with tick=10370; when recording ends the value reverts
> to tick=9998. In contrast, when recording with the pcHDTV HD3000 in
> DTV mode using over-the-air digital TV, the system clock is
> unaffected.
>
> Eventually I realized that this behaviour began after I "upgraded" to
> ivtv-0.10.0. When I revert to ivtv-0.8.1 the clock runs correctly.
> When I install the latest ivtv-0.10.1, the problem returns.
>
> Here's my setup:
> Athlon(tm) 64 Processor 3200+
> Fedora Core 6, kernel-2.6.19-1.2911.fc6 x86_64
> mythtv ver 0.20
> ivtv-0.10.0
> Hauppauge WinTV PVR 150, recording NTSC from cable
> pcHDTV HD3000, recording broadcast ATSC digital TV
>
> Questions:
>
> Does anyone else experience such a clock slowdown?
>
> Is there a fix?
I strongly suspect what is wrong. A patch for this is in progress and
I'll post a messages for people to test it when it is ready. Probably
this weekend, in fact.
I think that turning off any VBI support in MythTV might be sufficient
to workaround the problem.
Regards,
Hans
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