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STM32U575 Minimal Bootloader

A lightweight bootloader for the STM32U575 that resides at the start of internal flash and transfers execution to an application stored at a fixed offset.

Current Scope

  • Single application image
  • No A/B slots or rollback
  • No CRC or signature verification
  • No CAN-based update

Memory Map

0x08000000  Bootloader (64 KB)
0x08010000  Application
0x081FFFFF  End of flash

How It Works

On reset, the MCU begins executing the bootloader at 0x08000000. The bootloader reads the first two words at APP_START_ADDR and checks whether they form a valid application vector table. If valid, it transfers control to the application.

Vector Table

Every Cortex-M image begins with a vector table at its base address:

APP_START_ADDR + 0x00  Initial MSP
APP_START_ADDR + 0x04  Reset_Handler
APP_START_ADDR + 0x08  NMI_Handler
APP_START_ADDR + 0x0C  HardFault_Handler
...

The bootloader uses the first two entries to launch the application:

  • Word 0 — initial stack pointer (MSP)
  • Word 1 — application Reset_Handler address

The jump sequence:

  1. Disable interrupts
  2. Clear bootloader interrupt state
  3. Set SCB->VTOR = APP_START_ADDR
  4. Load the application MSP
  5. Branch to the application Reset_Handler

Linker Configuration

Bootloader

ROM origin = 0x08000000
ROM length = 64K

Application

ROM origin = 0x08010000
ROM length = remaining flash

Future Improvements

  • Bootloader entry condition (e.g. GPIO pin or flag)
  • CAN-based firmware update
  • Image metadata / header format
  • CRC or hash verification
  • Dual-slot updates with rollback support