[PYTHON] Hello, world! With virtual CAN communication

Overview

Let's simulate CAN communication used for in-vehicle embedded applications in a PC. You can read more about CAN in the article below. https://qiita.com/fattolys/items/e8f8081d3cb42d7da0f6

The following is the network configuration of the system created this time. Throw a CAN packet from Nord2 to Nord1.

environment

• Python 3.7
• Ubuntu 18.04

Create virtual interface

Create a virtual CAN interface with the following command.

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

If you hit ifconfig, you can see that vcan0 is added as shown below.

$ ifconfig
vcan0: flags=193<UP,RUNNING,NOARP>  mtu 72
        unspec 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  txqueuelen 1000  (UNSPEC)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Nord 1 code creation

Nord 1 will display the packets coming to vcan 0 sequentially.

vcan_nord_1.py

# ref: https://elinux.org/Python_Can
import socket
import struct

# CAN frame packing/unpacking (see `struct can_frame` in <linux/can.h>)
can_frame_fmt = "=IB3x8s"

def build_can_frame(can_id, data):
    can_dlc = len(data)
    data = data.ljust(8, b'\x00')
    return struct.pack(can_frame_fmt, can_id, can_dlc, data)

def dissect_can_frame(frame):
    can_id, can_dlc, data = struct.unpack(can_frame_fmt, frame)
    return (can_id, can_dlc, data[:can_dlc])

# create a raw socket and bind it to the given CAN interface
s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
s.bind(("vcan0",))

while True:
    cf, addr = s.recvfrom(16)
    print('Received: can_id=%x, can_dlc=%x, data=%s' % dissect_can_frame(cf))

Nord 2 code creation

Nord2 throws a "hellowld" packet to vcan0.

vcan_nord_2.py

# ref: https://elinux.org/Python_Can
import socket
import struct

# CAN frame packing/unpacking (see `struct can_frame` in <linux/can.h>)
can_frame_fmt = "=IB3x8s"

def build_can_frame(can_id, data):
    can_dlc = len(data)
    data = data.ljust(8, b'\x00')
    return struct.pack(can_frame_fmt, can_id, can_dlc, data)

# create a raw socket and bind it to the given CAN interface
s = socket.socket(socket.AF_CAN, socket.SOCK_RAW, socket.CAN_RAW)
s.bind(("vcan0",))

try:
    s.send(build_can_frame(0x01, b'hellowld'))
except socket.error:
    print('Error sending CAN frame')

Operation check

Start vcan_nord_1.py in the terminal and execute vcan_nord_2.py in another terminal. As shown below, the terminal on the vcan_nord_1.py side will show that the packet has arrived.

from now on

It might be interesting to make a car that runs within a 3DCG platform such as Unity using vcan communication.

Reference site

https://elinux.org/Bringing_CAN_interface_up https://elinux.org/Python_Can