refclock 28 gone wacky on me

Mike bellyacres at
Thu Jun 9 21:21:16 UTC 2016

I'm at a loss here as to why my offset on 28.1 is so far off. Typically 
the offset settles in around 0.008 and jitter around 0.004.  This has 
been setup from the microserver HOWTO nearly verbatim using clockmaker 
etc. etc. etc.  Certainly not placing any blame there, as previous 
setups following those steps haven't shown results this wacky.  I've 
checked everything I can think of.  Last run was around 24 hours with no 
change.  This afternoon, shut it all down, pulled battery on module, let 
go an hour restarted it all back up with same results right off.  I'd be 
grateful for any input, or suggestions at this point.

GPS module is a ST22, SkyTraq Venus 6 chipset.  Datasheet is here.

Raspberry Model B Revision 2.0, configured for the Uputronics HAT.

Linux rpi-ticker 4.4.11+ #888 Mon May 23 20:02:58 BST 2016 armv6l GNU/Linux
gpsd: 3.17~dev (revision release-3.16-346-g24cdae0)
ntpd 0.9.4-44652aa Jun  5 2016 02:25:36

352 ?        S<sl   0:39 /usr/local/sbin/gpsd -P /var/run/ 
354 ?        SLs    0:03 /usr/local/sbin/ntpd -p /var/run/ -N -g 
-u 105:110

ntpd is running as ntp:ntp

The output from ntpq -p that is relevant here.

xSHM(1)          .PPS.            0 l    8   16  377    0.000 -1001.1   
-SHM(0)          .GPS.            0 l    7   16  377    0.000 -363.77   

/etc/ntp.conf contents

statsdir /var/log/ntpstats/
statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable
server prefer minpoll 4 maxpoll 4
fudge refid PPS
server iburst
server iburst
server iburst
restrict default kod limited nomodify notrap nopeer noquery
restrict -6 default kod limited nomodify notrap nopeer noquery
restrict -6 ::1
server minpoll 4 maxpoll 4
fudge time1 0.210 refid GPS
driftfile /var/log/ntpstats/ntp.drift


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