DFU Bootloader
All STM32 MCUs have a built-in bootloader which will allow reflashing. The Boot0 pin is used to toggle between "normal" boot and this bootloader. Unfortunately this process can not be controlled without manipulating the Boot0 pin, so if we want to control this from our application, we will have to implement our own bootloader.
Overall Architecture
All STM32 MCUs (indeed all ARM processors) follows the Von Neumann architecture. This essentially - in this context - means that the instruction and data memory share the same address space. Since STM32 processors are 32-bit processors and since 32-bit addresses can address 4GB (4,294,967,296 bytes), sharing the address space between instruction and data memory is not a problem.
On STM32s, programs are stored in on-chip flash memory. Different STM32s have different amount of flash memory, but common for all is that it is mapped in the address space starting from 0x08000000.
| Start Addr | End Addr | Size (hex) | Size (kb) | ||
|---|---|---|---|---|---|
| End | --> | 0x8078000 | 0x8080000 | 0x8000 | 32kB |
| 0x8070000 | 0x8078000 | 0x8000 | 32kB | ||
| 0x8068000 | 0x8070000 | 0x8000 | 32kB | ||
| 0x8060000 | 0x8068000 | 0x8000 | 32kB | ||
| 0x8058000 | 0x8060000 | 0x8000 | 32kB | ||
| 0x8050000 | 0x8058000 | 0x8000 | 32kB | ||
| 0x8048000 | 0x8050000 | 0x8000 | 32kB | ||
| 0x8040000 | 0x8048000 | 0x8000 | 32kB | ||
| 0x8038000 | 0x8040000 | 0x8000 | 32kB | ||
| 0x8030000 | 0x8038000 | 0x8000 | 32kB | ||
| 0x8028000 | 0x8030000 | 0x8000 | 32kB | ||
| 0x8020000 | 0x8028000 | 0x8000 | 32kB | ||
| 0x8018000 | 0x8020000 | 0x8000 | 32kB | ||
| 0x8010000 | 0x8018000 | 0x8000 | 32kB | ||
| 0x8008000 | 0x8010000 | 0x8000 | 32kB | ||
| Begin | --> | 0x8000000 | 0x8008000 | 0x8000 | 32kB |
Under normal reset (Boot0 not activated), the MCU will jump to address 0x8000000 and begin execution from there.
| Start Addr | End Addr | Size (hex) | Size (kb) | Usage | ||
|---|---|---|---|---|---|---|
| End | --> | 0x8078000 | 0x8080000 | 0x8000 | 32 kB | Application (480 kB) |
| 0x8070000 | 0x8078000 | 0x8000 | 32 kB | |||
| 0x8068000 | 0x8070000 | 0x8000 | 32 kB | |||
| 0x8060000 | 0x8068000 | 0x8000 | 32 kB | |||
| 0x8058000 | 0x8060000 | 0x8000 | 32 kB | |||
| 0x8050000 | 0x8058000 | 0x8000 | 32 kB | |||
| 0x8048000 | 0x8050000 | 0x8000 | 32 kB | |||
| 0x8040000 | 0x8048000 | 0x8000 | 32 kB | |||
| 0x8038000 | 0x8040000 | 0x8000 | 32 kB | |||
| 0x8030000 | 0x8038000 | 0x8000 | 32 kB | |||
| 0x8028000 | 0x8030000 | 0x8000 | 32 kB | |||
| 0x8020000 | 0x8028000 | 0x8000 | 32 kB | |||
| 0x8018000 | 0x8020000 | 0x8000 | 32 kB | |||
| 0x8010000 | 0x8018000 | 0x8000 | 32 kB | |||
| 0x8008000 | 0x8010000 | 0x8000 | 32 kB | |||
| Begin | --> | 0x8000000 | 0x8008000 | 0x8000 | 32 kB | Bootloader (32 kB) |