[ntp:questions] Maximum time2 fudge value for NMEA refclock?

David J Taylor david-taylor at blueyonder.co.uk.invalid
Mon Jul 19 13:33:40 UTC 2010

"David Lord" <snews at lordynet.org> wrote in message 
news:qmldh7-k2e.ln1 at p4x2400c.home.lordynet.org...
> When I first tried parallel port PPS I had to google and
> unusually it didn't take much searching to find a bug report
> and that the issue was fixed in later versions of ntpd.
> I think it was [1238] fixed in ntpd-4.2.6
> The problem shows when the pps comes from another source,
> eg. gps2 and pps0 and the absence of serial DCD to gps2.

So the PPS and the "GPS" signals are not on the same port as far as NTP is 
concerned.  That's what you're say, I think?

> The fix by adding a fudge time1 is messy because it depends
> on the particular nmea sentences but so long as GPS is fudged
> to 30ms or so of the other servers the PPS kicks in ok.
> I've not found it possible to compile a more recent ntpd
> (4.2.6p1-RC4) on NetBSD as there seems to be many changes
> and a lot of magic required. I might download 4.2.4p6-o
> and see how the NetBSD version differs.
> David

I do recall Dave Hart looking at an issue like this where a PPS signal 
and, say, an Internet NTP source were available, so it's quite possible it 
has now been addressed.  Sorry to hear about the compiling problems.  On 
checking, it seems that the bug was fixed for 4.2.5p237-RC on 2009-Dec-26.


David (T) 

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