[ntp:questions] Re: Linux PPS triggering with NMEA

Ulrich Windl Ulrich.Windl at RZ.Uni-Regensburg.DE
Tue May 10 06:38:46 UTC 2005

Bjorn Gabrielsson <bg at lysator.liu.se> writes:

> Ulrich Windl <Ulrich.Windl at RZ.Uni-Regensburg.DE> writes:
> > 
> > You may play with some PPS API offset adjustments or NTP driver fudge flags.
> Could you elaborate on this. I have a system with refclock_NMEA,
> 2.4.21-nano-kernel. I want to adjust this system 13us. Another system
> need a little more than 2 ms adjustment. I have played with the
> "time1" fudge-factor -- not getting it right...

ppsctl says (among other things):
-oXY    Set PPS API offset for `X' events (a|c) to `Y'ns

That is, with "-oa123" you set an offset to assert events ('a') to
123ns. Similarly for 'c'lear events and negative numbers.

You should be able to set the correction outside of ntpd once the PPS API is
set up. I haven't tried ever, however.

The magic of "fudge1" should be explained in the various driver's
documentation pages.

Hope this help,

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