Setup NTP on compute board to serve time to Create® 3

Why should I do this?

ROS 2¹ is dependent upon synchronized clocks between nodes to have all data in the same reference time. When the Create® 3 is publishing on topics, it is publishing its data with the timestamp of its system clock, which synchronizes with an NTP server. If the Create® 3's Wi-Fi is connected to a network with internet connection, it will sync to a global time NTP server. The Create® 3 NTP config is also set to listen for servers on USB IP address 192.168.186.1 and 192.168.186.3. If the compute board is connected over USB to the Create® 3 with the compute board assigned one of these IP addresses on its USB interface, NTP on the compute board can keep the clocks between the compute board and Create® 3 in sync, even without an internet connection. If there is an internet connection on both compute board and Create® 3, configuring the NTP server on the compute board to serve the Create® 3 can still add value by reducing jitter between clocks. If your Create® 3 and compute board have an internet connection, this is not required, but is still recommended.

Step-by-step

On your Compute Board, install chrony NTP server package
```
sudo apt install chrony
```
Edit the config file
```
sudo vi /etc/chrony/chrony.conf
```

Add the following lines after the pool #.ubuntu.pool.ntp.org iburst maxsources # block

# Enable serving time to ntp clients on 192.168.186.0 subnet.
allow 192.168.186.0/24

Optionally add the following lines immediately afterward if your SBC will not have a connection to a reference clock (i.e., the Internet)
```
# Serve time even if not synchronized to a time source
local stratum 10
```
Restart chrony
```
sudo service chrony restart
```
Log into the Create® 3 web application and modify the NTP sources (as of Jul 2023 under "Beta Features") to add the following if it does not exist:
```
server 192.168.186.3 iburst
```
Through the Create® 3 web application, restart the NTPD server (or reboot the robot) if you made changes in the previous step.
Verify compute NTP server is talking to the Create® 3
```
sudo chronyc clients
```

Confirm 192.168.182.2 shows non 0 number in NTP column

Hostname                      NTP   Drop Int IntL Last     Cmd   Drop Int  Last
===============================================================================
192.168.186.2                  51      0   5   -    32       0      0   -     -

Note that if there is a large jump in the time, the Create® 3 may not accept it until its next reboot. This can be verified by checking the Create® 3 robot's log for a line like
```
user.notice ntpd: ntpd: reply from 192.168.186.3: delay ### is too high, ignoring
```
If this happens, simply restart the robot (not just the application) via the webserver over the network connection.

ROS 2 is governed by Open Robotics ↩