The clock synchronisation uses chrony which is a versatile implementation of the Network Time Protocol (NTP).
Chrony should be installed in all the robots (slaves) and the server used as a reference (master) :
sudo apt-get install chrony
The configuration of chrony is done in the file /etc/chrony/chrony.conf.
The configuration for slaves is available in ../tools/chrony.conf.
For a local network 192.168.team_id.0/8, master configuration is
local stratum 8
manual
allow 192.168.9.0/8
rtcsync
the slaves configuration is
server master_ip maxdelay 0.005 minpoll 0 maxpoll 0
allow 192.168.9.0/8
makestep 0.01 3
rtcsync
Stop current chronyd
sudo killall chronyd
Restart chronyd
sudo chronyd
From a slave, we can check the offset to master using
chronyc -n sources
To monitor the offset between master and robots, the script ../tools/chrony_monitoring.py can be used. The script shows the measured offset between the clocks in milliseconds. For example
./chrony_monitoring.py olive tom > /tmp/offsets.csv
and in an other terminal launch gnuplot and type
plot for [col=2:k] '/tmp/offsets.csv' using 0:col
where k is 1 plus the number of robots, so k=3 for our example.