Released: May, 2017 | Updated: June, 2020

Customizable Bootloader for STM32 microcontrollers. This project includes demonstrations for various hardware how to perform in-application-programming of a firmware located on external SD card with FAT32 file system.

Each example uses the same bootloader library located in the lib/stm32-bootloader folder. The examples are located in the projects folder and they come with a separate, dedicated README file with description related to that specific implementation.

Update: the STM32L496-Discovery example supports compiling and building the project with the GNU Arm Embedded Toolchain (ARM GCC) out-of-the-box, in addition to IAR EWARM. Check out the project README for further information.

Please refer to https://akospasztor.github.io/stm32-bootloader for complete documentation of the bootloader library source code.

Read more, clone or fork the project at my GitHub repository:


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Table of Contents

Bootloader features

Source code organization

├── docs
├── drivers
│   ├── CMSIS
│   └── STM32L4xx_HAL_Driver
├── lib
│   ├── fatfs
│   └── stm32-bootloader
└── projects
    ├── STM32L476-CustomHw
    ├── STM32L496-CustomHw
    └── STM32L496-Discovery

The docs folder contains the generated documentation of the bootloader source code and other documentation-related static files.

The drivers folder contains the CMSIS (Cortex Microcontroller Software Interface Standard) as well as the HAL (Hardware Abstraction Layer) drivers from ST.

The bootloader source code and corresponding header file can be found in lib/stm32-bootloader folder of the repository. Additionally, the lib folder contains the FatFs library as well.

The various demonstrations reside in the projects folder. Each example project contains an include and source folder where the header and source files are located respectively. The compiler and SDK-specific files are located in their respective subfolders. Furthermore, every example project has a dedicated README file explaining its functionality in detail.


The GitHub project repository contains the following examples. Each example has its own README file with detailed description located in the project repository.

Microcontroller Hardware Project path
STM32L476VG Custom projects/STM32L476-CustomHw
STM32L496VG Custom projects/STM32L496-CustomHw
STM32L496AG 32L496GDISCOVERY projects/STM32L496-Discovery

How to use

The bootloader can be easily customized and tailored to the required hardware and environment, i.e. to perform firmware updates over various interfaces or even to implement over-the-air (OTA) updates if the hardware incorporates wireless communication modules. In order to perform successful in-application-programming, the following sequence has to be kept:

  1. Check for flash write protection and disable it if necessary.
  2. Initialize flash with Bootloader_Init().
  3. Erase application space with Bootloader_Erase().
  4. Prepare for programming by calling Bootloader_FlashBegin().
  5. Perform programming by repeatedly calling the Bootloader_FlashNext() function. The programming procedure requires 8 bytes of data (double word) to be programmed at once into the flash. This function automatically increases the address where the data is being written.
  6. Finalize programming by calling Bootloader_FlashEnd().

The application image has to be in binary format. If the checksum verification is enabled, the binary must include the checksum value at the end of the image. When creating the application image, the checksum has to be calculated over the entire image (except the checksum area) with the following parameters:

Important notes:


The bootloader can be widely configured in the bootloader.h file. The file includes detailed comments and descriptions related to the configurable parameters and definitions.


[1] PM0214, "STM32F3 Series, STM32F4 Series, STM32L4 Series and STM32L4+ Series Cortex®-M4 Programming Manual", http://www.st.com/resource/en/programming_manual/dm00046982.pdf