Table of Contents

This is old and crusty. You have been warned!

ntp gps setup

This process has been complicated and messy, because of the combination of 1) I don't know what I'm doing, and 2) the resources on this are good but complicated. Almost everything I've figured out has come from these three pages:

I had to fill in a few holes here and there, so I am going to try and get a comprehensive guide in place here, because I will forget.

Setup

Guide

  1. Install and update ubuntu server on machine. Desktop works but server is lighter. This guide will also probably work for debian but I am writing it for ubu now because that's what I have working.
  2. Disable apparmor. This is a single purpose server. Apparmor is garbage and gets in the way of everything. Do so by: 
    sudo service apparmor stop
    sudo update-rc.d -f apparmor remove
  3. Prepare to build ntp with pps support (get all the bits) 
    # apt-get build-dep ntp
     # apt-get install pps-tools ubuntu-dev-tools
    # apt-get source ntp
    # cd ntp*
  4. Attempt to build. THIS WILL FAIL! Whatever. If not, who knows. 
    # dpkg-buildpackage -uc -us -nc
  5. It failed. Fix it by editing: 
    nano ntpd/refclock_jupiter.c
  6. Go to line 904. Comment it out as such 
    /* fprintf(stdout, buffer); */

    (yes this commenting could be done before the attempted build, but if it works before hand, you save a step. Compiling again after the failure is very fast anyway)

  7. Compile again 
    # dpkg-buildpackage -uc -us -nc
  8. Install! 
    # dpkg -i *.deb

    (the deb will be up a level)

  9. Configure udev rules to properly configure the devices at boot. 
    # Provide a symlink to /dev/ttyS0 and set low_latency for latency improvement
KERNEL=="ttyS0", SYMLINK+="gps0", MODE="0666"
KERNEL=="ttyS0", RUN+="/bin/setserial /dev/%k low_latency"
KERNEL=="ttyS0", RUN+="/usr/sbin/ldattach pps /dev/%k"

# Symlink /dev/pps0 to /dev/gpspps0
KERNEL=="pps0", SUBSYSTEM=="pps", DRIVER=="", SYMLINK+="gpspps0"
KERNEL=="pps0", GROUP="dialout"
KERNEL=="pps0", MODE="0666"

    For some reason, the ldattach bit never works for me and I have to run it manually after rebooting. This is a huge pain and I don't know how to fix it yet.

  10. Add user ntp to the dialout group 
    sudo gpasswd -a ntp dialout
  11. Configure /etc/ntp.conf as such:
    # /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

# Specify one or more NTP servers.
# local mess
server 127.127.20.0 mode 18 minpoll 4 iburst prefer true
fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 flag4 1

# Use time-a and b ntp servers as a fallback.
server time-a.nist.gov
server time-b.nist.gov

# By default, exchange time with everybody, but don't allow configuration.
restrict -4 default kod notrap nomodify nopeer noquery
restrict -6 default kod notrap nomodify nopeer noquery

# Local users may interrogate the ntp server more closely.
restrict 127.0.0.1
restrict ::1

# Clients from this subnet have unlimited access, but only if
# cryptographically authenticated.

restrict 10.0.0.0 mask 255.0.0.0 notrust

    Tweak as necessary. I don't know all the fudge flags yet. This can be improved.

  12. Restart ntp service 
    sudo service ntp restart
  13. Check ntpq -p output. If everything went well, you should see something like this:
    john@dc7900:~$ ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
oGPS_NMEA(0)     .GPS.            0 l    6   16  377    0.000    0.623   0.072
*time-a.nist.gov .ACTS.           1 u   25   64  373   91.647   36.162   4.774
+time-b.nist.gov .ACTS.           1 u   18   64  165   96.251   41.469   2.220

    If anything failed, check journalctl -xe to see if there are any hints. There almost always are.

  14. Just for funsies, ntpq -pcrv output:
    john@dc7900:~$ ntpq -pcrv
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
oGPS_NMEA(0)     .GPS.            0 l   15   16  377    0.000    0.492   0.044
+time-a.nist.gov .ACTS.           1 u   26   64  337   91.647   36.162   4.632
*time-b.nist.gov .ACTS.           1 u   23   64  257   92.135   38.865   4.538
associd=0 status=041d leap_none, sync_uhf_radio, 1 event, kern,
version="ntpd [email protected] Fri Feb 26 13:56:57 UTC 2016 (1)",
processor="x86_64", system="Linux/4.2.0-16-generic", leap=00, stratum=1,
precision=-21, rootdelay=0.000, rootdisp=0.979, refid=GPS,
reftime=da7ae733.9e1ec802  Fri, Feb 26 2016 10:01:07.617,
clock=da7ae742.600f0f00  Fri, Feb 26 2016 10:01:22.375, peer=45935, tc=4,
mintc=3, offset=0.492, frequency=22.723, sys_jitter=0.044,
clk_jitter=0.000, clk_wander=0.145

To D0 & Thoughts

Right now my offset and jitter can be improved. This can be done by: