GPS Time Synchonization

Preconditions: install, configure and enable gpsd by following this guide.

Install chrony

sudo apt install chrony

Edit /etc/chrony/chrony.conf, and add the following line at the end:

refclock SHM 0  delay 0.5 refid NMEA

Edit /etc/default/gpsd, and add options '-n -b':

# Devices gpsd should collect to at boot time.
# They need to be read/writeable, either by user gpsd or the group dialout.
DEVICES="/dev/ttyACM0"
# Other options you want to pass to gpsd
GPSD_OPTIONS="-n -b"

Restart gpsd and chrony:

sudo systemctl restart gpsd
sudo systemctl restart chrony

Done!

You can check if chrony receives time data from your GPS devices with chronyc sources

After around 30 seconds, you should see last sample data in the NMEA line, e.g:

210 Number of sources = 9
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
#- NMEA                          0   4   377    11    +73ms[  +73ms] +/-  251ms
^- pugot.canonical.com           2   6   377    53   +394us[ +394us] +/-   54ms
^+ chilipepper.canonical.com     2   6   377    54   +156us[ +185us] +/-   44ms
^- alphyn.canonical.com          2   6   377    52   +624us[ +624us] +/-  127ms
^+ golem.canonical.com           2   6   377    55   +324us[ +352us] +/-   53ms
^+ extern4.nemox.net             2   6   377    54   -177us[ -149us] +/-   48ms
^+ 194.112.182.172               2   6   377    55   -151us[ -123us] +/-   29ms
^* ntp.candystore.at             2   6   377    53   +132us[ +160us] +/-   23ms
^+ svn.mediainvent.at            2   6   377    55    -94us[  -66us] +/-   36ms