CANLogger

Standalone universal CAN bus logger. Reads frames from a vehicle CAN bus, packs them into MLVLG v2 format and writes to an SD card. Logs open in MegaLogViewer and UltraLog.

Two ideas drive the design:

• Universality. The device doesn't know ahead of time which IDs and fields it's going to log. The CAN → MLG mapping is defined by a config.ini file on the SD card, so a single firmware image works with different cars and protocols without recompilation.
• DIY-friendliness. An off-the-shelf STM32_F4VE board from AliExpress already provides the MCU, USB, SD slot, LEDs and buttons. Everything CAN-specific (transceiver, DC-DC, supercap, shutdown circuit, connectors) lives on a hat that can be built on a prototyping board or ordered as a PCB — all from standard, widely available components.

Hardware

• STM32F407VET6 @ 168 MHz (STM32_F4VE V2.0 board, off-the-shelf)
• CAN1 + TJA1050 / MCP255x transceiver, 125k / 250k / 500k / 1M
• SD card over SDIO 4-bit + FatFS
• USB CDC for config upload, diagnostics, and log download without ejecting the SD
• Buttons: K0 (MLG marker), K1 (graceful shutdown)
• Hat with CAN transceiver, DC-DC and supercap for a clean flush on power loss

Details: docs/HARDWARE.md.

Features

• Standard and extended (29-bit) CAN IDs
• U08/S08/U16/S16/U32/S32/S64/F32, scale/offset, LUT, sub-byte fields
• Plausibility filter with last_good / clamp / skip strategies and sensor presets (aem_uego)
• MLG v2 with markers and a synthetic Date field (Unix timestamp)
• LSE-backed RTC with VBAT battery — time set over USB CDC, survives resets
• Graceful shutdown on VIN drop: flush → f_sync → f_close, auto-resumes a new session after reset
• Recovery from SD errors: truncate → sync → close → remount → new file, without stopping logging
• Persistent fault log in RTC backup registers — the last fault is visible after reboot

Quick Start

1. Build the hardware per HARDWARE.md
2. Flash the firmware (see firmware/ and make flash)
3. Put config.ini in the FAT32 SD card root — examples live in firmware/test/
4. Insert the SD, power up — LED D2 on = logging
5. Power off (or press K1), remove the SD, open .mlg files in MegaLogViewer / UltraLog

USB CDC (/dev/cu.usbmodem… on macOS, /dev/ttyACM… on Linux) supports help, status, stream, ls, get, mark, settime. See docs/DEBUG.md.

Config Format

[logger]
interval_ms = 50          # 20 Hz snapshot rate
can_bitrate = 500000

[field]
can_id = 0x666
name = Coolant
units = C
start_byte = 1
bit_length = 8
type = U08
scale = 1.0
offset = -50.0
category = Engine

Full reference: docs/CONFIG_GUIDE.md.

Repository Layout

• firmware/Lib/ — pure C, host-tested with Unity, no HAL
• firmware/Src/ — HAL glue and CubeMX-generated code, edits only inside USER CODE sections
• firmware/test/ — host tests + config examples
• firmware/mlg-test/ — Node.js MLG validator
• hardware/ — reserved for KiCad projects of the hat (work in progress)
• docs/ — project documentation (see docs/README.md)

Build and Test

Prerequisites:

• STM32CubeIDE — used headless for building and for the bundled toolchain (arm-none-eabi-gcc, ST-LINK GDB server, STM32_Programmer_CLI)
• External ST-LINK/V2 dongle — the STM32_F4VE has a 20-pin JTAG/SWD header (P1), no onboard programmer
• gcc + python3 for host-side unit tests and CDC scripts (macOS: via Xcode CLT / brew)

All commands run from firmware/:

make build     # headless STM32CubeIDE build (Debug)
make test      # host unit tests (native gcc + Unity)
make flash     # flash the board over ST-LINK
make erase     # erase flash
make reset     # reset the MCU
make cdc-cmd CMD=status        # send a CLI command over USB CDC
make cdc-put FILE=config.ini   # upload a file to the SD over USB CDC

Debugging targets (ocd-server, ocd-debug, gdb-server, debug, gdb-read) are documented in docs/DEBUG.md.

Status

Firmware is working — it logs a Nissan ECU via the cansult bridge and an AEM X-Series UEGO lambda controller. Hat PCB is in progress (breadboard prototype validated). Current roadmap and open tasks live in docs/REQUIREMENTS.md.

License

MIT — see LICENSE.