STM32F4 SD Bootloader

A minimal bootloader for STM32F4 microcontrollers that reads Intel HEX firmware files from an SD card and programs them into sector-based flash memory. This bootloader supports FAT32 file systems and includes robust handling of extended addressing, checksum validation, and automatic flash erasure.

Features

• Parses and flashes Intel HEX files from /STM32-BOOT/app.hex
• Supports Intel HEX record types: DATA, EOF, ELAR (0x04), ESAR (0x02), and tolerates SLAR (0x05)
• Approximates the programmed image span to erase the required flash sectors
• Validates checksum for each HEX record before programming
• FAT32 SD card access through a sdFat32 file abstraction layer
• Dynamically saves the application's start address to /STM32-BOOT/app.addr, eliminating the need for hardcoded addresses and enabling flexible placement of the application in flash memory.
• Toggles LED on GPIOC Pin 13 during flashing and error states
• Deletes app.hex after a successful update to prevent reprogramming

Usage

1. Format your SD card with FAT32.
2. Place the app.hex file into a folder named STM32-BOOT at the root of the SD card.
3. Insert the SD card into your STM32F4-based board.
4. On power-up or reset, the bootloader will:
   • Initialize the SD card and FAT32 file system
   • Check for a valid app.hex
   • Estimate the programmed span and erase the overlapping flash sectors
   • Program the firmware to internal flash memory
   • Save the start address to app.addr
   • Delete app.hex
   • Light the LED to signal completion or turn off on error

The application image must start above the bootloader region. In the current layout, that means the HEX image must not begin at or below 0x08003FFF.

Flash Sector Map

The bootloader uses a fixed STM32F4 sector map covering:

0x08000000 - 0x08003FFF  (Sector 0)
0x08004000 - 0x08007FFF  (Sector 1)
...
0x080E0000 - 0x080FFFFF  (Sector 11)

Sector 0 (0x08000000 - 0x08003FFF) is reserved for the bootloader itself. The application image should be linked to start in sector 1 or above.

The erase range is estimated from the Intel HEX file size, then aligned to the flash sectors that overlap the target address range.

LED Status (GPIOC Pin 13)

• Blinking: Flash programming in progress
• ON: Flashing completed successfully
• OFF: Error during flashing (e.g., checksum or HAL failure)

Dependencies

This bootloader depends on the sdFat32 library for FAT32 file access. Ensure it's included and integrated properly.

To clone this project with submodules:

git clone --recurse-submodules https://github.com/pdlsurya/stm32f4-sd-bootloader.git

Functions Overview

Function	Description
bootloaderInit()	Initializes the SD and FAT32 system
firmwareUpdateAvailable()	Checks for presence of app.hex
updateFirmware()	Erases flash, writes firmware, saves app address, deletes hex
getAppStartAddress()	Loads the application start address from app.addr
APP_START(addr)	Jumps to application at specified address

License

MIT License – feel free to use, modify, and distribute this project.