PM0056 STM32F10xxx Cortex-M3 programming manual, страница 93, B, BL, BX, and BLX Branch instructions. Syntax
B{cond} label
BL{cond} label
BX{cond} Rm
BLX{cond} Rm
● ‘Rm’ is a register that indicates an address to branch to. Bit[0] of the value in Rm must
be 1, but the address to branch to is created by changing bit[0] to 0.