STM32 bootloader for firmware upgrades

The device is an USB key with STM32F103 including a capacitive button. The code will be released as open source which allows to reuse already existing open source libraries for certain features, in order to minimize your effort. Suggested approach: 1. User keeps button pressed while connecting (and powering up) the device to the USB port of computer. 2. Bootloader starts and checks: A) If button is pressed then boot the bootloader's upgrade functionality (which is the case in this example) B) Else if button is not pressed then the firmware is executed. 3. For case A, a virtual FAT mass storage device is started. This contains a short text file which describes how to flash the device. The implementation of FAT file system is already available as Petit FatFS: [login to view URL] 4. The user copies the downloaded firmware file to the mass storage device. As a consequence the firmware is send to the bootloader. 5. Bootloader downloads and verifies the first few bytes which contain the following meta information: - Version number of upgrade needs to be higher than current firmware - Firmware is compatible to device series - Size: The firmware upgrade fits into the available flash memory (firmware_size <= total_flash_size - bootloader_size) 6. If the verification is okay then the bootloader overwrites the current firmware with the new firmware. It also stores the new firmware version. In case the verification failed, an error message will be "stored" in the text file on the (virtual) mass storage device. Priority: - Clean and safe programming approach which includes proper code documentation to allow review and later improvements. - Small size: The code must be optimized in order to result in a small binary. Further information: - GCC to be used for compilation (some STM32 flavours exist) - Test platforms will be Windows, Linux and MacOS X. - Development includes defining a simple file format to store the firmware's meta information. This means to define which bytes are used for which meta information. A simple (Linux or Windows) tool or script to create those files would be required. Expected meta information: * Version number of firmware upgrade * Device series - You might reuse any of these bootloaders or libraries: [login to view URL] If you intent to do so, please let me know in advance.