Setting up CAN on a Pi

The Subsystems Computer's interface to the firmware

Linux has support for the CAN protocol when using an external chip, but it needs to be enabled and configured before it can be used. We use the MCP2518FD` chip on a custom-built Pi hat to achieve this, and this page describes how to set up the chip on a fresh Raspberry Pi.

The CAN0 overlay

First, we need to tell the Pi how to interface with the chip. The Raspberry Pi works with a "device tree" that tells it what hardware to use and how to find it. We will add our own file to this tree and modify the boot config to expose this device to the operating system.

First, add the following to a new file, titled mcp2518fd-can0.dts:

// TODO: Find this code

Compile this file to a .dtbo and copy it to the boot directory:

dtc -@ -I dts -O dtb mcp2518fd-can0.dts -o mcp2518fd-can0.dtbo
cp mcp2518fd-can0.dtbo /boot/overlays

Now add the following lines to the end of /boot/config.txt:

# MCP2518FD CAN chip support
# TODO: Verify this
[all]
dtparam=spi=on
dtoverlay=mcp2518fd-can0,oscillator=16000000,interrupt=25,spimaxfrequency=1000000

The command line

Reboot the Pi. Now that the hardware has been configured, it's time to set up CAN as a network device in the operating system.

First, update your software packages:

sudo apt update
sudo apt upgrade
sudo reboot

Then, use the ip tool to register CAN:

sudo ip link add can0
sudo ip link set can0 up type can bitrate 500000

The bitrate must match the one registered in config.txt and the one used on the firmware. The add command needs to be run just once, but the set command needs to be run on every boot. This can also be done by the Subsystems program.

Testing

The can-utils package offers tools to quickly test the CAN bus. Run sudo apt install can-utils to install the tools, then use cansend to send data and candump to receive data. One quick test is to open two terminals and run candump can0 in one and cansend can0#deadbeef in the other. Note that at least one other CAN-capable device must be connected and listening for messages in order for the bus to work.

More Resources

• The MCP2518FD chip

• Raspberry's docs on Device Trees

• Using dts and overlays

• The can-utils tool