Verified - ntpd ignores the year part of refclock timestamps

Eric S. Raymond esr at
Thu Aug 31 03:41:05 UTC 2017

Hal Murray <hmurray at>:
> >> How many of the NMEA devices have GPS rollover problems?
> >> (either now or soon)
> > It's impossible to tell.  When a device will roll over is, because of the
> > pivot-date trick, not a function of its hardware type but of its firmware
> > release. --  
> Are there any known examples?

We had a tracker issue relating to this on an OnCore GT.  I think the
submitter promised a patch, but it hasn't landed.

I'm pretty sure I've seen one or two descriptions of people coping
with rollovers on time-nuts while chasing possible sources for old
refclock types.

It's not exactly a *common* problem - most people who buy consumer-grade
GPSes don't seem to keep them in service that long.

I've never seen it myself.  I have one device that might be old enough -
one of the original DeLorme Earthmates from the eatly nineties - but I haven't
powered it up in a *long* time; not sure it still works.

> I have a collection of NMEA toys.  I don't remember seeing GPS rollover on 
> any of them.  Some of them are quite old, but I don't think any have reached 
> 20 years yet.

Right. You'd have to watch for 19.2 years after you acquired the device to be
*sure* of seeing it roll over.

> We could test fixup software by setting the system clock ahead far enough to 
> look like GPS had rolled over.

What kind of fixup?  I looked long and hard at this problem in the
context of GPSD.  I never found one that wasn't as bad - or worse -
than relying on the sysrem clock date.
		<a href="">Eric S. Raymond</a>

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