[ntp:questions] Large and apparently permanent step in PPM error - confused?
david.cureton at dcureton.com
Sat Nov 1 00:47:59 UTC 2008
I am syncing a Linux 2.6.26 kernel to a Serial DCD PPS GPS source.
The kernel time has been running for quite some time with a ~160ppm
frequency error however inexplicably the ppm error over night simply
jumped to ~105ppm. The system has for the last couple of day tracked in
a stable manner at that ~105ppm rather than the ~160ppm offset it used
There has been no change to the system that I am aware of. The machine
was not rebooted. There has been no dramatic change in temperature
although I think temperature change would be very dramatic cause 55ppm jump.
(In fact you can see the daily temperature variation in the ppm error
which is in the order of a couple of ppm over time)
I have a plot of the kernel offset and ppm error as well as the time
offset to a stable GPS steered internet peer in my area.
I am at a loss to explain why this jump occurred and whether to expect
it to occur in the future. Does anyone have any ideas to the cause of
this jump in PPM error. System is on a UPS so unlikely to be a power
supply issue. I am stumped?
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