[ntp:questions] NTP and PPS (and gpsd etc..)

David Anullo david_anullo at itacosystems.com
Thu Apr 26 08:43:42 UTC 2007


Jason Rabel wrote:
> David,
>
> I have a Jupiter 8 unit that I am using the Jupiter Refclock and it works
> perfect. However I looked over the specs for the Jupiter 21 and it only
> supports SiRF and NMEA. AFAIK there is no SiRF refclock.
>
> With the older Jupiter modules you have to use them in their Binary mode,
> using them in NMEA can cause a 1-2 second offset because of the delay in
> processing NMEA output from the module. I don't know if that is still true
> for the newer modules, but I would assume it's entirely possible. Even if
> the time info was wrong you can use just the PPS signal from the GPS via the
> PPS/ATOM refclock, then use another NTP server for the general time info.
>
> The catch here is: exactly what OS are you running? You said "linux embedded
> machine", which by default linux does not support a PPS signal. You have to
> patch the kernel to get PPS support. On the other hand FreeBSD supports PPS
> and also has nanosecond precision.
>
> Jason
>
> _______________________________________________
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> questions at lists.ntp.isc.org
> https://lists.ntp.isc.org/mailman/listinfo/questions
>
>   
Ops, i'm sorry...i use a machine with thinstation 2.2 system and a linux 
2.6.16.5 (i have patched the kernel with de Giometti's patch..).
Now i try to use NMEA with ntp 4.2.4 (Udo van den Heuvel's ntpd NMEA 
patch) <http://time.qnan.org/linux2.6-pps/ntpd-nmea.patch>. I find this 
procedure on http://time.qnan.org/.

I must debugging some code because i have big problem with 
time_pps_create function on time_pps.h (refclock_nmea.c) and i have 
created a "personal" patch (the old code try to use a inexistent filedes 
even if in the comment say "/* We simply ignore "filedes" */")

Now i have a jitter that sometimes "go away" but i think it's possible 
that in some case i lost a satellites cover..

Thanks to all.

-- 
David Anullo

Itaco S.r.l.
Via Zoe Fontana, 220 Ed. B1
00131 ROMA - ITALY
Tel. +390641294922 - Fax +39064191740
www.itacosystems.com




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