At this point, the CAN interface has to be initialized manually after every reboot. Therefore, if the Pi is used as a permanent controller, it might be preferable to have these initialization steps been carried out during startup.
In order to achieve that, can2upd
is going to be registered as a service and started right after the can0
interface has been initialized. Raspbian is using systemd
as service manager, so this post will describe how to create systemd
units for the tasks described above. Information about how systemd works and how to create unit configuration files can be found in the systemd(1)
Linux manual page or in Justin Ellingwood’s excellent article on DigitalOcean .
The CAN interface initialization service
Create a new unit configuration file using
sudo vim /lib/systemd/system/socketcan-interface.service with the following contents.
The can0
interface should be initialized as soon as networking is available, which should be the case on runlevel 3 that translates to multi-user.target
for systemd
. Since all commands used in this unit will exit after completion, the type has to be set to oneshot
along with the RemainAfterExit=
option set to yes
. Multiple commands have to be separated with ;
. Executing
1 2 3 |
sudo chmod 644 /lib/systemd/system/socketcan-interface.service sudo systemctl daemon-reload sudo systemctl enable socketcan-interface.service |
will set permissions and enable the unit.
The can2udp service
After the can0
interface has been setup, can2udp
has to be started. Since it is desirable to collect as much information as possible about the system’s state, can2udp
will be run in foreground mode, allowing the verbose option to be activated. The output can be retrieved later using journalctl, see the troubleshooting section for more information. Create a new unit configuration file using
sudo vim /lib/systemd/system/can2udp.service with the following contents.
Putting socketcan-interface.service
in both the After=
and Requires=
section will make this service run after socketcan-interface.service
has been started and will attempt to start it in case it’s not running. Executing
1 2 3 |
sudo chmod 644 /lib/systemd/system/can2udp.service sudo systemctl daemon-reload sudo systemctl enable can2udp.service |
will set permissions and enable the unit.
Conclusion
After both systemd
units have been created and enabled, the Raspberry PI has to be rebooted. From this point, whenever the PI starts, the can0
interface will be up and running with a proper baudrate and can2udp
will be started waiting for incoming UDP connections on its default port.
Troubleshooting
An overview of all running systemd
units can be found using
sudo systemctl list-units. Both the socketcan-interface.service
and the can2udp.service
unit should be listed as loaded and active. Since the socketcan-interface
is of type oneshot
, it will be marked as exited while can2udp
should be indicated as running.
Log output of the respective units can be viewed using
sudo journalctl -u can2udp or
sudo journalctl -u socketcan-interface. Linux will buffer the output written by can2udp
and not write it to /var/log/
per line. Because of that, no output of can2udp
might appear in the logs at first. Sending a few commands will cause the logging buffer to flush and the logs to appear in the journalctl
output.