[ntp:questions] offline machines' time synchronization

Chris Albertson albertson.chris at gmail.com
Fri May 25 17:50:03 UTC 2012

On Fri, May 25, 2012 at 12:29 AM, Terje Mathisen <"terje.mathisen at
tmsw.no"@ntp.org> wrote:

> Chris Albertson wrote:
>> Next how to get the PPS to be at the top of the second.  Two methods
>> 1) don't bother.  Linux PPS will log the time of both the GPS's PPS
>> and the Rb PPS.  Read the log file to determine the offset.  This give
>> offset with uSec precision.  To get better you need a hardware time
>> interval counter.  I happen to have a few of those and can read
>> sub-nanoseconds but this is gross overkill.  Microseconds are good
>> enough for NTP......
> Much simpler would be to use a fudge command to specify the current phase
> offset between the Rb and GPS PPS signals, i.e. if the Db happened to start
> out 367 ms off, just let ntpd know that these pulses are supposed to have
> such an offset.
Yes, correct the "fudge" method is what I was getting at in #1 above.   I
assumed that every on here would know to use the measured difference in a
"fudge" but the key is measuring the offset.   Get that from the log file.
or a TIC if you have one.

But there is a problem in the even with the best Rb the offset will drift
over time.

Chris Albertson
Redondo Beach, California

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