VBBoot

VBBoot is a minimal CAN bootloader for STM32G431.

The bootloader:

• checks application validity at startup and jumps to app if valid;
• otherwise stays in boot mode and accepts firmware frames over Classic CAN 2.0 (FDCAN_FRAME_CLASSIC, no FD/BRS);
• writes firmware to flash at 0x08003000..0x0801FFFF.

Boot Transport (CAN)

• CAN ID is node_id (standard 11-bit identifier).
• RX/TX use the same CAN ID.
• ACK payload is 1 byte: 0xD0 (done) or 0xE0 (error).

Supported commands

• BOOT_CMD_START (0x01)
  • Part 0 frame: [0x01, 0x00, size_u32_le(4), crc32_low16_le(2)]
  • Part 1 frame: [0x01, 0x01, crc32_high16_le(2)]
• BOOT_CMD_DATA (0x02)
  • Frame: [0x02, data...]
  • Data is buffered and written to flash in 8-byte aligned chunks.
• BOOT_CMD_DONE (0x03)
  • Finalize, verify size + CRC32, ACK and jump to app on success.

BOOT_CMD_GET_ID enum value exists in code (0x05) but is not handled in transport state machine.

node_id source (EEPROM)

node_id is read from external I2C EEPROM (same idea as VBDrive config backend):

• I2C bus: I2C2 (hi2c2)
• EEPROM device address: 0x50
• EEPROM offset: 0x0000
• Record format:

typedef struct __attribute__((packed)) {
    uint32_t magic;      // must be NODE_ID_MAGIC (0x424C4E49)
    uint8_t node_id;     // valid range: 1..127
    uint8_t reserved[3];
} NodeIdRecord;

If EEPROM is not ready, read fails, magic is invalid, or node_id is out of range, bootloader uses DEFAULT_NODE_ID (0x69).

Build

Use CMake presets (toolchain is configured in cmake/gcc-arm-none-eabi.cmake):

cmake --preset RelWithDebInfo
cmake --build build/RelWithDebInfo

Or explicitly:

cmake -S . -B build/RelWithDebInfo -DCMAKE_BUILD_TYPE=RelWithDebInfo \
  -DCMAKE_TOOLCHAIN_FILE=cmake/gcc-arm-none-eabi.cmake
cmake --build build/RelWithDebInfo

Post-build artifacts:

• VBBoot.elf
• VBBoot.hex
• VBBoot.bin

Flash layout

• Bootloader flash region: 0x08000000, length 12K (see linker script).
• Application start: 0x08003000 (APP_START_ADDR).

Python CAN test

Test script is in tests/test_bootloader_fdcan.py.

Example:

pytest tests/test_bootloader_fdcan.py \
  --hex=/path/to/app.hex \
  --can-iface=socketcan \
  --can-channel=can0 \
  --ack-timeout=0.8 \
  --node-id=0x69