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?
--
David A. De Graaf DATIX, Inc. Hendersonville, NC
[EMAIL PROTECTED] www.datix.us
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