[LinuxPPS] setting an offset

[clemens at dwf.com]

> 
> To summarize:
> NTPD-ATOM_CLOCK has a working ns-enabled offset as "fudgetime1" 
> in /etc/ntp.conf.
> PPS by implementing RFC 2783 has the variables PPS_OFFSETASSERT and 
> PPS_OFFSETCLEAR doing theirs, which are hopefully set to 0 in ntp-like 
> applications.
> 
> 
Not necessarily true.
The ONCORE driver uses this offset, changing it at every PPS event.
The Hardware itself can only provide the PPS pulse at the zero-crossings of its
clock, but KNOWS how far that is off from the true position.  As such it provides
in the text message what is referred to as the negative sawtooth correction for the
next PPS event.

Every second I read the negative saw-tooth, and set the OFFSET for the next 
PPS event.

This number is only a few nanoseconds, but every bit helps...
-- 
                                        Reg.Clemens
                                        reg at dwf.com