[ntp:questions] offline machines' time synchronization
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
More information about the questions