Example Linux (Ubuntu) Setup

This setup is for Raspberry Pis running Ubuntu and similar Debian distros.

1. Install MCP251XFD required drivers (example showing can-utils).

   sudo apt update
   sudo apt install -y can-utils
   

2. Enable SPI and add the MCP2518FD overlay.

   sudo nano /boot/firmware/config.txt
   

   # Add the following lines to config.txt:
   dtparam=spi=on
   dtoverlay=mcp251xfd,spi0-0,oscillator=40000000,interrupt=22,spimaxfrequency=10000000
   

3. Reboot the system.

   sudo reboot
   

4. Run CAN.
   • For CAN classic setup (example for 500 kbps, 87.5% sample point, bus error reporting):

     sudo ip link set can0 down 2>/dev/null || true
     sudo ip link set can0 type can bitrate 500000 sample-point 0.875 berr-reporting on
     sudo ip link set can0 up
     

   • For CAN FD setup (example for 1 Mbps nominal rate, 80% sample point, 4 Mbps data phase rate, bus error reporting):

     sudo ip link set can0 down
     sudo ip link set can0 type can bitrate 1000000 sample-point 0.80 dbitrate 4000000 dsample-point 0.80 fd on berr-reporting on
     sudo ip link set can0 up
     

Automatically Starting the CAN Interface

The ip link commands above do not persist across reboots. Use one of the methods below to bring can0 up automatically at boot. Both assume steps 1-3 of the setup above are complete and can0 shows up in ip link show.

Option A: systemd Service (Recommended)

A small systemd unit that runs the same ip link commands whenever can0 appears. This works on any systemd-based distro regardless of which network manager is in use.

1. Create the service file.

   sudo nano /etc/systemd/system/can0.service
   

2. Add the following contents.
   • For CAN classic (500 kbps, 87.5% sample point, bus error reporting): ```ini [Unit] Description=SocketCAN interface can0 BindsTo=sys-subsystem-net-devices-can0.device After=sys-subsystem-net-devices-can0.device

   [Service] Type=oneshot RemainAfterExit=yes ExecStartPre=-/usr/sbin/ip link set can0 down ExecStart=/usr/sbin/ip link set can0 type can bitrate 500000 sample-point 0.875 berr-reporting on restart-ms 100 ExecStart=/usr/sbin/ip link set can0 up ExecStop=/usr/sbin/ip link set can0 down

   [Install] WantedBy=sys-subsystem-net-devices-can0.device

    - For CAN FD (1 Mbps nominal, 80% sample point, 4 Mbps data phase, bus error
      reporting), replace the first `ExecStart=` line with:
   ```ini
   ExecStart=/usr/sbin/ip link set can0 type can bitrate 1000000 sample-point 0.80 dbitrate 4000000 dsample-point 0.80 fd on berr-reporting on restart-ms 100
   

3. Enable and start the service.

   sudo systemctl daemon-reload
   sudo systemctl enable --now can0.service
   

Notes:

• WantedBy=sys-subsystem-net-devices-can0.device starts the service as soon as the kernel creates can0, so it does not race the MCP251XFD driver during boot. BindsTo= stops it again if the device disappears.
• restart-ms 100 automatically recovers the controller 100 ms after a bus-off event. Without it, the interface stays down after bus-off until it is manually restarted, which is usually undesirable for an unattended system.
• To change the bitrate later, edit the file, then run sudo systemctl daemon-reload && sudo systemctl restart can0.service.

Option B: systemd-networkd

If the system already uses systemd-networkd (the default on Ubuntu Server via netplan), CAN settings can be declared in a .network file instead.

1. Create the network file.

   sudo nano /etc/systemd/network/80-can0.network
   

2. Add the following contents.
   • For CAN classic (500 kbps, 87.5% sample point, bus error reporting): ```ini [Match] Name=can0

   [Link] RequiredForOnline=no

   [CAN] BitRate=500000 SamplePoint=87.5% BusErrorReporting=yes RestartSec=100ms

    - For CAN FD (1 Mbps nominal, 80% sample point, 4 Mbps data phase, bus error
      reporting), replace the `[CAN]` section with:
   ```ini
   [CAN]
   BitRate=1000000
   SamplePoint=80%
   DataBitRate=4000000
   DataSamplePoint=80%
   FDMode=yes
   BusErrorReporting=yes
   RestartSec=100ms
   

3. Enable systemd-networkd (if not already enabled) and apply the config.

   sudo systemctl enable --now systemd-networkd
   sudo networkctl reload
   sudo networkctl reconfigure can0
   

Notes:

• RequiredForOnline=no prevents systemd-networkd-wait-online from delaying boot while waiting for the CAN interface.
• On Ubuntu Desktop, NetworkManager does not manage CAN interfaces, so enabling systemd-networkd alongside it is safe as long as only CAN interfaces are matched by files in /etc/systemd/network/.

Verifying CAN Interface

After a reboot, confirm the interface came up with the expected settings:

ip -details link show can0

Look for state UP, can state ERROR-ACTIVE, and the configured bitrate/ dbitrate. For Option A systemd services, the service status and logs are available with:

systemctl status can0.service
journalctl -u can0.service

Then check for traffic with can-utils:

candump can0