RP2040 gs_usb compatible USB CAN

Raspberry Pico (RP2040) gs_usb compatible firmware interfacing CAN bus via cheap MCP2515 CAN controller.

Hardware

Adafruit RP2040 CAN Bus Feather

Raspberry Pico with MCP2515 CAN module

CAN Transceiver TJA1050 on CAN module requires 5V, but Raspberry Pico is not 5V tolerant. So the path on the module should be cut off and 5V wire should be soldered directly on TJA1050 Pin 3 like on the following image:

MCP2515 CAN module	Raspberry Pico
TJA1050 VCC 5V - Pin 3	VBUS
VCC	3v3 OUT
GND	GND
SS	GP17
SO	GP16
SI	GP19
SCK	GP18
INT	GP20

1 Mbit bitrate can be enabled by replacing CAN module crystal with 20 Mhz one and changing MCP2515_OSC_FREQ variable.

Build

1. install Raspberry Pico SDK
2. make sure environment variable PICO_SDK_PATH points to installed SDK

$ mkdir build
$ cd build
$ cmake ..
$ make -j$(nproc)

Flash

Enter flashing bootloader via:

1. Keep BOOTSEL button pressed
2. Reset the board with button or re-plugging power
3. Release BOOTSEL button

Load the firmware via picotool load gs_usb_ADAFRUIT_CAN_FEATHER.uf2 command or by copying that file into connected USB mass storage provided by RP2040 BOOT ROM. Reset the board afterwards.

Use

You should see can0 interface once the device is connected to USB.

$ ip a
...
96: can0: <NOARP,ECHO> mtu 16 qdisc noop state DOWN group default qlen 10
    link/can

Now you can configure bitrate and bring interface up:

$ sudo ip link set can0 type can bitrate 500000
$ sudo ip link set can0 up

You can receive and send messages with can-utils package:

$ candump can0
$ cansend can0 123#DEADBEEF

Use following udev rule for more predictable interface name and reload with udevadm control --reload-rules:

# /etc/udev/rules.d/79-can.rules
ACTION=="add", ENV{ID_SERIAL}=="D_rp2040-can_123456", NAME="mycan"

Interface may be managed with systemd-networkd:

# /etc/systemd/network/can.network
[Match]
Name=mycan
# or apply same config to all CAN interfaces
#Type=can

[CAN]
BitRate=500000

Tests

Both tests requires two CAN interfaces connected to single host.

hw_test.py

$ RP2040_IFACE=mycan TEST_IFACE=othercan pytest

Stress testing

Fully utilizes CAN bus by spamming randomly generated messages in a loop. All messages are also verified on receiver side.

$ make tests/stress
$ ./tests/stress mycan othercan
$ ./tests/stress othercan mycan