[ntp:questions] How to determin hardware latency for PPS offset given simple tools.

Paul G bodosom at gmail.com
Fri Jun 21 14:15:41 UTC 2013

On Thursday, June 20, 2013 5:51:50 PM UTC-4, E-Mail Sent to this address will be added to the BlackLists wrote:
> enable stats [etc. etc.]

As noted earlier I've done that or it's not applicable.  E.g. I only use the
PPS driver and my seconds are numbered by an appliance that doesn't run ntpd.

>  On one system at a time, ...
>   have several other NTP servers configured {I usually shoot for 6 to 10}

I don't have six to ten stratum one servers (but maybe I should) and it doesn't
seem useful to compare my << 500 microsecond offsets to non-local clocks.

>    with all involved systems continuously running for more than one day;
>     take an average ...

In another thread (and some here) I explain how I've done that and I don't
really like the e.g. 124 microsecond time1 I derived.  However it does result
in O(1) microsec. offsets between some of my clocks.

>  perhaps the PPS signal is inverted?

It's not.

> It seemed like David Taylor covered that on may 25th.

Yes.  While I appreciate the suggestions and the good will behind them they don't seem informed by my question/problem description.

My key point is that ntpq appears to be telling me odd things.  E.g. my network
is low latency, symmetric and consistent but some of my offsets are one or two
orders of magnitude beyond other offsets.

So my question is how to find what I hope is hardware latency using the tools
at hand or the coverse given multiple S1 clocks with O(10) microsecond offsets
which one is right.

I expect I will move a set of them to a 10/100 switch and see if that makes a

Ideally all my clocks pairs would look like this (both have time1 0):

localhost oPPS(0) .PPS. ... 377    0.000    0.001   0.001
black     +aster  .PPS. ... 377    0.065   -0.003   0.004

localhost oPPS(0) .PPS. ... 377    0.000    0.000   0.004
aster     +black  .PPS. ... 377    0.066    0.007   0.010

But maybe some of them are just not up to the task:
aster     *ntp1   .PPS. ... 377    0.526    0.129   0.166

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