USB CAN-FD Module

A compact, open-source USB-to-CAN FD adapter built around the RP2354A MCU and the Microchip MCP251xFD CAN FD controller. Plug it into any machine over USB-C and get a bus-powered, SocketCAN-compatible CAN / CAN FD interface — no external power needed.

Status: Hardware complete. Firmware and the Linux SocketCAN driver are implemented and build cleanly, but are not yet validated on real hardware.

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Features

• CAN 2.0 A/B and CAN FD (up to 64-byte payloads, bit-rate switching)
• Native SocketCAN integration on Linux (canX interface, can-utils)
• Host-controlled bitrate, mode, bus-off restart, and on-board 120 Ω termination
• Transmit confirmation, bus-error reporting, and CRC-checked USB framing
• Bus-powered USB-C; per-device serial number from the chip UID

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How it works

  CAN bus ─── MCP251xFD ──SPI── RP2354A ──USB(bulk+control)── Host ── SocketCAN (canX)
                                  │
                core0: CAN/SPI   core1: USB (TinyUSB vendor class)

The firmware bridges the MCP251xFD to the host over a small CRC-framed USB vendor protocol (core 0 drives CAN over SPI, core 1 drives USB; lock-free queues connect them). The Linux kernel module presents that as a standard SocketCAN network device. The wire protocol is defined once in src/common/usb_can_protocol.h and shared by both sides — see the Host Protocol Guide to implement your own host driver or library.

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Repository layout

src/
├── common/              # Shared USB wire protocol + CRC32 (firmware & host)
├── rp2354a_firmware/    # RP2354A firmware (C, Pico SDK)
└── drivers/
    └── lw_can_kmod/     # Linux SocketCAN kernel module
external/
└── lw_mcp251xfd/        # MCP251xFD driver library (git submodule)
docs/                    # Documentation (see firmware_todo.md)
schematics/              # PCB schematics (SVG + PDF)

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Building

Clone with submodules (the MCP251xFD library is a submodule):

git clone --recurse-submodules https://github.com/LeoTheWizard/usb_can_fd_module.git
cd usb_can_fd_module
# already cloned without submodules? — git submodule update --init

Firmware (RP2354A)

Requires the Pico SDK (RP2350-capable), CMake ≥ 3.13, and the arm-none-eabi GCC toolchain.

cmake -S src -B src/build -DPICO_SDK_PATH=/path/to/pico-sdk -DPICO_BOARD=pico2
cmake --build src/build

Output: src/build/rp2354a_firmware/usb_can_fd_firmware.uf2.

Linux driver

Requires kernel headers for your running kernel (linux-headers-$(uname -r)), make, and GCC.

cd src/drivers/lw_can_kmod
make                      # -> build/lw_can.ko

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Usage

1. Flash the firmware. Hold BOOTSEL, plug the module into USB; it mounts as a mass-storage device. Copy the UF2 onto it — the board reboots and runs the firmware:

cp src/build/rp2354a_firmware/usb_can_fd_firmware.uf2 /run/media/$USER/RP2350/

2. Load the driver (the dependency must be loaded first; insmod does not resolve it):

sudo modprobe can-dev can can-raw
sudo insmod src/drivers/lw_can_kmod/build/lw_can.ko
dmesg | tail            # expect: "lw_can registered (can0)"

3. Bring up the interface and use it with can-utils:

# Classic CAN at 500 kbit/s
sudo ip link set can0 up type can bitrate 500000

# …or CAN FD: 500 kbit/s arbitration, 2 Mbit/s data phase
sudo ip link set can0 up type can bitrate 500000 dbitrate 2000000 fd on

candump can0                    # receive
cansend can0 123#DEADBEEF       # send a classic frame
cansend can0 123##1112233       # send an FD frame (BRS)

sudo ip link set can0 down      # when finished

After a bus-off, recover with sudo ip link set can0 type can restart, or add restart-ms 100 at link-up for automatic recovery.

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Hardware

Component	Details
MCU	Raspberry Pi RP2354A (RP2350 family, dual Arm Cortex-M33)
CAN FD controller	Microchip MCP251xFD (SPI)
Host interface	USB-C — bus-powered
CAN connector	2-pin PicoBlade (CAN H / CAN L), switchable 120 Ω termination

Schematics: MCU · CAN FD · Power · Interfaces · full PDF

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License

MIT — © Leo Walker, 2025