pico-multi-bridge

Raspberry Pico (RP2040) multifunctional USB bridge, consisting of
gs_usb compatible firmware for interfacing CAN bus via can2040 and a cheap CAN transceiver,
and multiple USB CDC serial "adapters".

Hardware

CAN Transceivers often run off of 5v. Make sure to get one that can be controlled over 3.3V! I used an MCP2562, which does not support 3.3v on the output side, and has an extra pin vor logic voltage.

Pin	What it do
TXD	Set can2040 tx pin to this
Vss	GND
Vdd	5v
RXD	Set can2040 rx pin to this
STBY	HIGH = transceiver off, pulled up
CANH	CAN out
CANL	CAN out
Vio	3.3v / µC comms voltage

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_PICO_CAN2040.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