Config is as follows:
driftfile /var/lib/ntp/ntp.drift
## kernel pps driver
server 127.127.22.1 minpoll 4 maxpoll 4 prefer
fudge 127.127.22.1 refid PPS flag3 1
# NMEA source
server 127.127.28.0 minpoll 4
fudge 127.127.28.0 refid GPPS
# other time sources on LAN with GPS/GLONASS/DCF77/etc
peer neo
peer hetlicht
peer clara
peer nanosg20
peer china
server agps iburst minpoll 1 maxpoll 4
server artc iburst minpoll 1 maxpoll 4
# upstream servers
server ntp.xs4all.nl iburst
server ntp.nmi.nl iburst
server chime1.surfnet.nl iburst
server ntp0.nl.uu.net iburst
restrict -4 default kod notrap nomodify
restrict -6 default kod notrap nomodify
restrict 127.0.0.1
restrict ::1
disable auth
broadcast 172.29.0.255
> You don???t give your config, but as using the shared memory driver works, do
> you have a prefer peer active when you are using the atom driver? If there
> isn???t one, that will cause the ref clock to be falseticker???d?. Your atom
> jitter isn???t the issue.
So what you're saying is that the atom should not be the preferred one?
I'll give that a try.
Thanks
> "Ceux qui sont prêts à abandonner une liberté essentielle pour obtenir une
> petite et provisoire sécurité, ne méritent ni liberté ni sécurité."
> Benjimin Franklin
>
> > Le 9 mars 2015 à 10:52, folkert <[email protected]> a écrit :
> >
> > Hi,
> >
> > I have a raspberry pi with a gps connected to it.
> > It runs linux kernel 3.18.5+ and ntp version 1:4.2.6.p5+dfsg-2.
> > When I use my own rpi_gpio_ntp which is a userspace program, I get
> > something like:
> >
> > remote refid st t when poll reach delay offset jitter
> > ==============================================================================
> > *127.127.28.1 .PPS. 0 l 8 16 377 0.000 -0.010 0.008
> >
> > *127.127.28.1 .PPS. 0 l 11 16 377 0.000 0.005 0.012
> >
> > *127.127.28.1 .PPS. 0 l 12 16 377 0.000 0.005 0.012
> >
> > *127.127.28.1 .PPS. 0 l 1 16 377 0.000 0.001 0.011
> >
> > (I omitted the peers)
> > So the jitter is around 8us. Not bad for userspace.
> >
> > Linux has this PPS interface for a while so now that it is easy
> > configurable in config.txt on the rpi, I thought I give that a try. The
> > strange thing now is that using that I get very bad jitter. So bad that
> > ntp discards it as a false ticker!
> >
> > remote refid st t when poll reach delay offset jitter
> > ==============================================================================
> > x127.127.22.1 .PPS. 0 l 2 16 377 0.000 0.161 0.001
> >
> > x127.127.22.1 .PPS. 0 l 7 16 377 0.000 0.148 0.006
> >
> > x127.127.22.1 .PPS. 0 l 13 16 377 0.000 0.147 0.007
> >
> > x127.127.22.1 .PPS. 0 l 2 16 377 0.000 0.146 0.006
> >
> > This is odd: the pps interface should work way better due to lower
> > latency etc.
> >
> > What could be going wrong here?
> >
> > The one at the top (28.1) uses GPS and the one at the bottom uses a
> > combined Glonass/GPS receiver. Note that I also swapped tried using pps
> > with 28.1 and rpi_gpio_ntp on 22.1 and then 28.1 fails and 22.1 is fine.
> >
> >
> > Folkert van Heusden
> >
> > --
> > Curious about the inner workings of your car? Then check O2OO: it'll
> > tell you all that there is to know about your car's engine!
> > http://www.vanheusden.com/O2OO/
> > ----------------------------------------------------------------------
> > Phone: +31-6-41278122, PGP-key: 1F28D8AE, www.vanheusden.com
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Folkert van Heusden
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