[ntp:questions] Adjusting PPS offset

A C agcarver+ntp at acarver.net
Sun Sep 4 05:38:54 UTC 2011

On 9/3/2011 22:21, unruh wrote:
> On 2011-09-03, A C<agcarver+ntp at acarver.net>  wrote:
>> I'm still digging through code for PPS and NMEA plus the routines in the
>> OS so that part is going to take a long time for me to figure out.  So
>> for now I'm just going to stick with PPS only and the pool servers.  As
>> for PPS itself, what is the proper (or at least most reasonable way) to
>> adjust the time1 offset so that PPS agrees with the tick of UTC?
> And how would you decide what that offset was? Since the PPS is almost
> certainly the most accurate time you have already.
> (actually it is off by about 1us due to the interrupt handling.)

Well, after leaving ntpd running for about a week straight, six network 
servers have settled down to report an average 2 ms offset (according to 
ntpq).  Each of the offsets is within about 0.5ms of each other.  The 
offset shown on PPS was 0.000 with a small amount of jitter.

I figured that if the entire collection of servers had settled into a 
2ms offset then the tick of PPS was probably off by that amount.

If that's not a reasonable assumption then what would be?

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