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How to use the RaspberryPi with MCP2518FD to debug UAVCAN

We will have to do a lot of testing to get the Viper quadcopter flying and to 107-Arduino-UAVCAN library. So we need a proper test system. I think most of the users here use a computer or a notebook and some type of slcan adapter.

I didn’t want to risk to corrupt my working system by installing lots of software so I decided to use a Raspberry Pi and set up the system there. There are some CAN boards on the market but most of them use a MCP2515 CAN controller which has no CAN FD and they also don’t have the connector specified by the dronecode standard.

That’s why my first step was to design a new HAT with the MCP2518FD controller. This controller supports CAN FD and it is has also drivers in the mainline raspbian distribution.

This is how the board looks in CAD:


The board has only a few components:

  • the MCP2518FD CAN controller
  • a TCAN332 CAN transceiver which also supports CAN FD
  • a switch to enable the termination resistor
  • the JST GH connectors
  • a terminal header to connect other CAN devices
  • and a few LEDs to show the status

In reality it looks like this:


It plugs directly ontop of a Raspberry Pi. In my case I used a Raspberry Pi 4.

The HAT is open source hardware and all the data is available on github:

To enable the HAT and the CAN controller in raspbian you simply have to edit /boot/config.txt and add line:

dtoverlay=mcp251xfd,spi0-0,oscillator=20000000,interrupt=25

keep care that you choose the right interrupt and SPI CE line and populate the corresponding resistor.

To enable CAN after boot up you have to enter:

sudo ip link set can0 up type can bitrate 250000

And that’s it. Now the interface is available as can0. You can show all CAN traffic by typing candump -decaxta can0 or use yakut to transmit and receive UAVCAN messages.

The whole test setup with DUT looks like this:

The Raspberry Pi can be accessed via WiFi so no more cables are necessary. You could also use cable LAN or directly connect a screen and a keyboard.

The HAT has also the possibility to supply power into the CAN systems. So small sensor nodes wouldn’t even require additional wiring.

I hope this helps to setup a proper test environment.

But I also have to confess that there is still a little problem: it seems like the MCP2518FD is sometimes missing some frames. Especially when there is a high load on the system. Maybe the receive interrupt isn’t handled properly. I will have to dig deeper into that but I think this could be only a minor issue.

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