[ntp:questions] offline machines' time synchronization

unruh unruh at invalid.ca
Fri May 25 21:51:49 UTC 2012


On 2012-05-25, Chris Albertson <albertson.chris at gmail.com> wrote:
> 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.

Yes. but slowly (probably about 1 sec per millenium or less)

>
>
>
> Chris Albertson
> Redondo Beach, California



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