[ntp:questions] Unstable Windows system clock when running 3rd party software component

Geir G geir.guldstein at start.no
Sat Jun 3 20:04:47 UTC 2006


Hello,

We use NTP to time synchronize our Windows-based data
collection/gateway systems. We have been running our software along
with ntpd.exe successfully for several years. However, we are now
facing a problem which I need help to resolve. Please note that I don't
think there is anything wrong with ntpd.exe. I think I must ask our
sub-vendor(s) the correct critical questions, and hope someone can help
with formulating those questions.

Platform: Embedded hardware platform. Pentium III 700MHz CPU. Windows
XP Embedded (Service Pack 2 level).
NTP version: 4.2.0, downloaded from http://norloff.org/ntp/

The system clock is stable if we run NTP and our software in
configurations like we have used previously. However, we have started
utilizing a 3rd party software component (an OPC server) in some
configurations, and it is in these configurations we experience
problems with unstable system clocks.

I have tried to isolate the problem the following way:

1. I start NTP. The system clock is stable and ntpq output indicates
"everything's fine". NTP generates no entries in the event log after
startup.

2. I start the 3rd party OPC server. I run ntpq -p and see a steadily
increasing offset. It seems the OPC server influences the system clock
negatively, and NTP finally has to reset the clock (event log entries):
time reset +6.023474 s
frequency error 6476 PPM exceeds tolerance 500 PPM
NTP continues to reset the clock as long as the OPC server is running.
This happens with about 15 minute intervals.

3. I stop the 3rd party OPC server. After some time the system clock is
again stable and ntpq output indicates "everything's fine". NTP
generates no entries in the event log.

4. I start the 3rd party OPC server again. The result is as described
in step 2 above.

I can't find anything in the OPC server documentation that indicates
that it performs adjustments to the system clock.

Which questions should I ask the OPC server and/or embedded hardware
vendor? I am course also happy if someone has advise on further things
to be checked.

Thanks in advance.

Geir




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