Verified - ntpd ignores the year part of refclock timestamps
Eric S. Raymond
esr at thyrsus.com
Thu Aug 31 03:41:05 UTC 2017
Hal Murray <hmurray at megapathdsl.net>:
> >> 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
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.
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