CAN Primer

On OreSat, two CAN 2.0A (aka classic CAN with 11-bit identifier) buses are used for the main communication bus between OreSat cards.

See the Wikipedia page for CAN at https://en.wikipedia.org/wiki/CAN_bus for the basics, it is fairly complete. No reason to repeat it here.

Virtual CAN Bus

Linux natively supports vcan (Virtual CAN) bus. A vcan bus can be super useful for development.

To make a vcan bus on Linux:

$ sudo ip link add dev vcan0 type vcan
$ sudo ip link set vcan0 up

Software Utilities

candump

The candump utility from the can-utils package can be used to monitor the raw CAN message over a CAN bus. The first column is the CAN bus being monitored, the second column is the COB-ID in hex, and the third column is the size of CAN message (0 to 8), and the rest is the CAN message as an octet string (hex values separated by spaces).

$ candump vcan0
  vcan0  710   [1]  05
  vcan0  080   [0]
  vcan0  710   [1]  05
  vcan0  610   [8]  40 18 10 00 00 00 00 00

For more info, see https://manpages.debian.org/testing/can-utils/candump.1.en.html

cansend

The cansend utility from the can-utils package can be used to send message over the CAN bus.

$ cansend vcan0 190#05.10

$ candump vcan0
  vcan0  190   [2]  05 10

For more info, see https://manpages.debian.org/testing/can-utils/cansend.1.en.html

SavvyCAN

An open-source and cross platform GUI that can display CAN traffic, as well as, record and view CAN traces. It can also use a .dbc file to parse the CAN messages. Incredibly usefully to monitor and debug CAN traffic.

See https://github.com/collin80/SavvyCAN

Hardware

A CANable can be used to connect to a CAN bus with a laptop. These are not needed if using a vcan (virtual CAN) bus for development.

Bash command to connect to a CANable using the slcand firmware.

$ slcand -o -c -s8 /dev/ttyACM1 can0

Bash command to connect to a CANable using the candlelight firmware with a bitrate of 1Mbps.

$ sudo ip link set can0 type can bitrate 1000000
$ sudo ip link set can0 up

Example systemd-networkd config file to autoconnect to a CANable using the candlelight firmware.

 # /etc/systemd/network/50-can.network

[Match]
Name=can0

[Link]
RequiredForOnline=no

[CAN]
BitRate=1M