1_TransmittingCAN.md

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Writing a Python script to transmit CAN-packages

This guide shows how simple it is to transmit CAN-packages within a Python script on a running embedded Linux system. It is a part of my "Mapping HPS Peripherals, like I²C or CAN, over the FPGA fabric to FPGA I/O and using embedded Linux to control them"-guide, where I show the complete development process with the FPGA design and bootloader creation (see here).

• To start the CAN0 execute this command on rsyocto to enable the CAN network Port:

  ip link set can0 type can bitrate 125000
  ip link set up can0

• Install python-can with python pip on the running rsyocto

  pip3 install python-can

Use Visual Studio Code Insider to debug this python-can application remotely (see here). Or use the onboard nanoeditor to write the python code.

• Create a new Python file, for example:

  nano sendCanPackage.py

• Insert the following lines to this Python file as shown in the python-can documentation

  #!/usr/bin/env python
  # coding: utf-8
  
  #
  #This example shows how sending a single message works.
  #
  
  import can
  
  def send_one():
  
  	# This uses the default configuration (for example from the config file)
  	# See: https://python-can.readthedocs.io/en/stable/configuration.html
  
  	# Using specific buses work similarly:
  	bus = can.interface.Bus(bustype='socketcan', channel='can0', bitrate=12500)
  	# ...
  
  	msg = can.Message(arbitration_id=0xAC,
  		  data=[0xAB, 0xAC, 0xAD, 0xAE],
  		  is_extended_id=False)
  
  	try:
  		bus.send(msg)
  		print("Message sent on {}".format(bus.channel_info))
  	except can.CanError:
  		print("Message NOT sent")
  
  
  if __name__ == '__main__':
  	send_one()

• Save and close this Python file or start a debugging session with Microsoft Visual Studio Code Insider

• Connect to the Adrunio Pin D8 to CAN TX and the Pin D9 to CAN RX on a 3.3V Can-Bus Transceiver

• Execute the Python script

  python3 sendCanPackage.py

• Debugging of this code with Visual Studio Code Insider

• Now the Cyclone V SoC-FPGA transmits a CAN package through the Arduino header with the ID 0xAC and the Payload 0xABACADAE:

  root@cyclone5:~# python3 sendCanPackage.py
  Message sent on socketcan channel 'can0'

  

If no one acknowledged this package the Bosch CAN-Controller re-transmits the package with the maximum available resources automatically until an ACK happens.

The embedded Bosch CAN-Controller can also detect linkage errors. In case of a missing connection to a CAN-Bus member a Linux Kernel Message will be triggered and the CAN Controller shuts down. Use the following command to restart the CAN-Controller:

link set down can0
ip link set up can0

For reading the CAN-BUS network statistics type:

ifconfig can0

In the same way it is also possible to communicate via UART, SPI or I²C. On rsyocto Python scripts for these use cases are pre-installed.

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