[ntp:questions] Getting NTP to correct only the clock skew

Spoon root at localhost.invalid
Sat Mar 31 11:52:15 UTC 2007


Steve Kostecke wrote:

> Spoon wrote:
> 
>> Is it possible to run NTP in a mode where it does not try to correct
>> the time offset, but only correct the frequency offset (skew)?
> 
> Yes.
> 
> Provide your ntpd with a stable PPS source and use the Undisciplined
> Local Clock.

I am running Linux 2.6.20.3-rt8

I don't think vanilla 2.6 supports PPS sources at the moment?

http://lkml.org/lkml/2007/2/16/303

Surely there must be some experimental patches?

http://unix.freshmeat.net/projects/ppskit/
http://www.kernel.org/pub/linux/daemons/ntp/PPS/

In my situation, I don't care what time it is, but my clock needs
to tick at the correct rate.

I've found the following articles:

http://www.ntp.org/ntpfaq/NTP-s-config-adv.htm#S-CONFIG-ADV-PPS
http://www.cis.udel.edu/~mills/ntp/html/pps.html

Can you suggest additional resources?

I think I can't use GPS because the computer is located in
a server room underground.

Are there other PPS sources? I've read about rubidium and cesium clock 
sources. How expensive are they? Do they come on a PCI board that can 
fit inside a 1U case?

Regards.




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