[ntp:questions] GPS/PPS and "enable calibrate"
Horvath Bob-BHORVAT1
Bob.Horvath at motorolasolutions.com
Wed Sep 4 22:05:22 UTC 2013
I am trying to get a raspberry pi GPS-based stratum server functioning and I am confused how to use the "enable calibrate" function.
I think I have figured out that to calibrate, you do the following:
1. Add "enable calibrate" to ntp.conf
2. "true" on "PPS" server line
3. "noselect" on the "GPS" reference clock to keep it from being used as a time source
4. "prefer" on a legitimate good time server.
5. "time1=0.0" on "GPS" fudge line
The calibration will take the PPS to be a good PPS signal, and will get the time of day from the "preferred" server.
After a while, you can
1. Take out "enable calibrate"
2. Leave "true" there?
3. Take out "noselect"
4. Move "prefer" to the GPS line?
5. Change time1= ????
Or do I just leave it as I configured it the first time?
Here is my ntp.conf as it stands right now...
# /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help
driftfile /var/lib/ntp/ntp.drift
# Enable this if you want statistics to be logged.
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
# Access control configuration; see /usr/share/doc/ntp-doc/html/accopt.html for
# details. The web page <http://support.ntp.org/bin/view/Support/AccessRestrict
ions>
# might also be helpful.
#
# Note that "restrict" applies to both servers and clients, so a configuration
# that might be intended to block requests from certain clients could also end
# up blocking replies from your own upstream servers.
# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default kod notrap nomodify nopeer
restrict -6 default kod notrap nomodify nopeer
# Local users may interrogate the ntp server more closely.
restrict 127.0.0.1
restrict ::1
# pps-gpio on /dev/pps0
server 127.127.22.0 minpoll 4 maxpoll 4 true
fudge 127.127.22.0 refid PPS
fudge 127.127.22.0 flag3 1 # enable kernel PLL/FLL clock discipline
# gpsd shared memory clock
server 127.127.28.0 minpoll 4 maxpoll 4 noselect # PPS requires at least one pre
ferred peer
fudge 127.127.28.0 refid GPS
fudge 127.127.28.0 time1 +0.0 # coarse processing delay offset
server 129.188.147.100 iburst
server 10.177.0.120 iburst prefer
enable calibrate
... and here is what my ntpq -pn looks like....
(Looking at it now, I am not sure how much this will tell since it hasn't been running very long)
pi at ntpi ~ $ ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
o127.127.22.0 .PPS. 0 l 2 16 377 0.000 -0.007 0.002
127.127.28.0 .GPS. 0 l 1 16 377 0.000 -82.005 56.615
+129.188.147.100 129.188.147.99 2 u 15 64 37 1.400 2.213 0.321
*10.177.0.120 .GPS. 1 u 15 64 37 27.184 -0.826 0.117
pi at ntpi ~ $
As you can tell from the reaches, I just recently rebooted, so it has only been running several minutes. If I remove those lines, I get something like this....
pi at ntpi ~ $ ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
127.127.22.0 .PPS. 0 l - 16 0 0.000 0.000 0.000
127.127.28.0 .GPS. 0 l 14 16 1 0.000 50.397 0.002
+129.188.147.100 129.188.147.99 2 u 15 64 1 1.394 509.349 0.197
*10.177.0.120 .GPS. 1 u 16 64 1 27.503 506.499 0.188
pi at ntpi ~ $
The server is a raspberry pi with the Adafruit MTK339 GPS chipset. It is running the image from here... http://ntpi.openchaos.org/downloads/
BTW, thanks to all the raspberry pi NTP guys out there that have gotten me this far!!
Bob
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