STMicroelectronics STM32 F101xx

The bootloader is a small program stored in the internal boot ROM memory (system memory) of STM32 devices. It is programmed by ST during production. The bootloader's main task is to download the application program to the internal Flash memory through one of the available serial peripherals (USART, CAN, USB, etc.). A communication protocol is defined for each serial interface, with a compatible command set and sequences.

The bootloader is automatically activated by configuring the BOOT0 and BOOT1 pins in the specific "System memory" configuration and then by applying a reset. Depending on the used pin configuration, the Flash memory, system memory or SRAM is selected as the boot space.

System memory boot mode must be exited in order to start execution of the application program. This can be done by applying a hardware reset. During reset, the BOOT pins (BOOT0 and BOOT1) must be set at the proper levels to select the desired boot mode. Following the reset, the CPU starts code execution from the boot memory located at the bottom of the memory address space starting from 0x0000 0000.

Depending on the used STM32 device, the bootloader may support one or more embedded serial peripherals used to download the code to the internal Flash memory. The bootloader identifier (ID) provides information about the supported serial peripherals.

For STM32F101xx and STM32F103xx XL-density devices (these devices have two Flash memory banks: Bank 1 and Bank 2), an additional boot mechanism is available which allows booting from Bank 2 or Bank 1 (depending on the BFB2 bit status (bit 19 in the user option bytes @ 0x1FFFF800)).