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	32 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

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)

Miscellaneous Links

• Excellent writeup about DFU bootloader