CANbus

This section explains setting up a CANbus network between 2 BBB and sending CAN messages using linux CAN-Utils. This page is primarily for understanding CANbus comms and is not directly required for using the X2. Also, most of the commands stated here are included in the BBB Scripts.

We use BeagleBoneBlack with a comms cape for communicating on the CAN network. BBB has 2 CAN controllers: DCAN0 and DCAN1. But the pins for DCAN0 are used by the comms cape, so we will be using DCAN1 exclusively. Note that these capes already have a terminating resistance (120Ω) between CAN-H and CAN-L.

Note: CANbus is a physical/data link later protocol. CANOpen is a higher layer protocol.

Configuring the BBB CAN interface

  1. We will be using DCAN1 controller on BBB for CAN comms. For this pins P9_24 and P9_26 have to be configured correctly. You can check current config by running config-pin -q P9.24. If it is configured for CAN, it will shows "p9_24 Mode: can".
  2. To config pins for CAN: sudo config-pin p9.24 can and sudo config-pin p9.26 can.

  3. Load LKMs for CAN:

    dmesg|grep can sudo modprobe can sudo modprobe can-dev sudo modprobe can-raw lsmod|grep can mesg|grep raw

  4. Setup the CAN link: sudo ip link set can1 up type can bitrate 1000000. The 1000000 can be replaced with your required bitrate. Then run sudo ifconfig can1 up.

    Note: sudo ifconfig can1 down can be used to close the network interface. This is useful if you want to change parameters, like bitrate.

  5. You can run ifconfig to check that the CAN interface is running. You should see CAN as one of the adapters along with ethernet.

Testing CAN messages between BBB

BBB distro Debian 9 onwards comes preinstalled with can-utils. We can use this send and received messages over CAN bus.

  1. Wire up the BBBs by connecting CAN-H to CAN-H, CAN-L to CAN-L, and common grounds. Do note that the last device in the daisy chain should have a 120Ω terminating resistance between CAN-H and CAN-L. This is already included in the BBB Comms cape.
  2. Setup the DCAN1 controller on BBB for CAN using steps above.
  3. On one of the BBB, send a can message using cansend can1 123#fe.ed.be.ef. On the other BBB, run candump can1. Note that the message and node ID used here are arbitrary since candump will read all messages being sent through the canbus.