Created November 5, 2024

Astrial - CAN

The goal of this tutorial is to communicate with CAN between 2 Astrial boards using the integrated CAN controller on Astrial and a CAN Hat.

Things used in this project

Hardware components

Astrial

Raspberry Pi Compute Module 4 IO Board

Waveshare CM4-IO-BASE-A Board

Waveshare RS485 CAN HAT (B)

CAN FD 3 Click

Female/Female Jumper Wires

Story

YouTube video and GitHub repository

For the step-by-step video you can see our YouTube channel

For a more in-depth guide, we've created a detailed tutorial hosted on GitHub. In this tutorial, you'll find step-by-step instructions, code examples, and additional resources to help you better understand and implement the concepts discussed here. Whether you're a beginner or looking to deepen your knowledge, this comprehensive guide covers everything you need.

You can access the GitHub repository with the full code here: https://github.com/System-Electronics/astrial_tutorials/tree/main/09-CAN

Introduction

In this tutorial, we'll walk you through the process of using two Astrial devices to communicate with each other using the CAN-bus protocol. We'll cover the necessary hardware setup, software installation, and scripts to send and receive messages over CAN-bus.

We will use one Astrial to communicate with Astrial's integrated CAN controller along with CAN FD 3 Click transceiver, and then we'll use Waveshare's CAN Hat.

Note that for this tutorial we used two different carrier boards, but you can use two of the same type.

Hardware setup

To use Astrial's integrated CAN controller you first need to set your CAN FD 3 Click to communicate using 3.3V instead of 5V (if you don't do this you might damage permanently your Astrial). To do this you will need to desolder a 0Ω resistor from the CAN FD 3 Click VIO SEL 5V and solder it on 3V3.

1 / 2 • Desolder the 0Ω resistor indicated in the picture from 5V and put it on 3V3 to select the correct Voltage

After doing this connect the transceiver to your Astrial using the GPIOs on the carrier as shown in the schematics.

To use the CAN Hat instead you will only need to connect it to the board using the GPIO header.

When both are connected correctly connect the hat CAN port to the FD3 Click serial port.

1 / 2

Software setup

Python packages

Install the required package to use the CAN Hat on the Astrial on which you're going to use it with:

pip3 install spidev==3.6

Enable the CAN interface

To enable the CAN, you need to select the 'imx8mp-astrial-flexcan2.dtb' device tree file in the U-Boot menu as shown here.

From the CAN hat Astrial to the FD3 Click Astrial

To receive messages on Astrial's CAN controller follow these steps on the CAN hat Astrial:

Set up CAN: launch this command to establish CAN link with the desired bitrate (we are using 125000 but you can choose other values)

ip link set can0 up type can bitrate 125000

Make the Astrial listen for messages: to be able to receive messages we are going to use a specific command which prints to terminal every received message over CAN-bus

candump can0

Now let's move on the other Astrial so that we can send messages to be seen on this one:

Use the default Device Tree Blob (DTB): to enable SPI communication, you need to upload the default Device Tree to your Astrial board if you modified it previously. You can find the DTB in the resources folder of the GitHub repository for this tutorial. If you are not sure how to do this, please refer to our GitHub guide.
Copy the custom MCP2515 library: we provide in our GitHub guide a custom version of the Adafruit's MCP2515 library in the main folder of this tutorial. Copy the can_lib folder to the Astrial, together with the example scripts.
Use the Python script to send data: run the python script named can_send.py that will send the message 'hello' every second on the bus.

python3 can_send.py

You will now see the 'hello' messages appearing on the FD3 Click Astrial's terminal.

From the FD3 Click Astrial to the CAN hat Astrial

Let's now do the opposite, sending message from the FD3 Click Astrial to the CAN hat Astrial.

On the CAN hat Astrial:

Create and run the Python script to receive data: create a Python script that implements the code provided in the Code section of this article named can_listen.py that will display on your terminal all the CAN messages it receives on the bus.

python3 can_listen.py

On the FD3 Click Astrial:

Use the cangen command to send messages: to send messages over CAN-bus there are some terminal commands, for example cangen will start sending random messages at regular intervals on the CAN-bus and you should be able to see them on your other Astrial with the CAN hat.

cangen can0

Code

# SPDX-FileCopyrightText: Copyright (c) 2020 Bryan Siepert for Adafruit Industries
#
# SPDX-License-Identifier: MIT

from can_lib.canio import Timer
from can_lib.canio import RemoteTransmissionRequest, Message
from can_lib import MCP2515 as CAN

mcp = CAN(baudrate=125000)

t = Timer(timeout=5)
next_message = None
message_num = 0
while True:
    # print occationally to show we're alive
    if t.expired:
        print(".", end="")
        t.rewind_to(1)
    with mcp.listen(timeout=1.0) as listener:
        message_count = listener.in_waiting()

        if message_count == 0:
            continue

        next_message = listener.receive()
        message_num = 0
        while not next_message is None:
            message_num += 1

            msg = next_message
            print("ID:", hex(msg.id), end=",")
            if isinstance(msg, Message):
                if len(msg.data) > 0:
                    print("Data:", end="")
                    message_str = ",".join(["0x{:02X}".format(i) for i in msg.data])
                    print(message_str)

            if isinstance(msg, RemoteTransmissionRequest):
                print("RTR_LEN:", msg.length)
            next_message = listener.receive()

Astrial - CAN

Things used in this project

Hardware components

Story

YouTube video and GitHub repository

Introduction

Hardware setup

Software setup

Python packages

Enable the CAN interface

From the CAN hat Astrial to the FD3 Click Astrial

From the FD3 Click Astrial to the CAN hat Astrial

Schematics

CAN FD3 Click Schematic

Code

can_listen.py

can_send.py

Credits

Andrea Torlai

Comments

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Astrial - CAN

Astrial - CAN

Things used in this project

Hardware components

Story

YouTube video and GitHub repository

Introduction

Hardware setup

Software setup

Python packages

Enable the CAN interface

From the CAN hat Astrial to the FD3 Click Astrial

From the FD3 Click Astrial to the CAN hat Astrial

Schematics

CAN FD3 Click Schematic

Code

can_listen.py

can_send.py

Credits

Andrea Torlai

Comments