Still struggling with the STM32F051C8T6 bootloader
Section 2.5 of the reference manual states that the system memory (which contains the bootloader factory-loaded into the part) is activated when BOOT0 is maintained high at startup and nBOOT1 is set to 1 (BOOT1 set to 0).



Section 4.1.1 of the same manual states that the default value of nBOOT1 is indeed 1. So it seems that all you need to start the bootloader is to set the BOOT0 pin to high at startup.



Then you can execute the loaded code by setting BOOT0 to low at startup. When BOOT0 is low, the code from the embedded flash is executed irrelevant of the state of nBOOT1.