[ntp:questions] Large and apparently permanent step in PPM error - confused?

David J Taylor david-taylor at blueyonder.neither-this-part.nor-this-bit.co.uk
Sat Nov 1 19:30:39 UTC 2008

David Cureton wrote:
> Hi,
>    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
> to be.
> 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?
> Thanks,
> David

Crystals can sometimes jump in frequency, although I'm surprised to see a 
modern unit do so, and that is quite a large step.  How old is the system?


More information about the questions mailing list