Important facts about the stm32 in general and for programming it

• Multiple external pins can be associated to interrupts
• Clock must be initialized by software. The stm32 is able to detect a failure of the external clock and fall-back on the internal clock and issue an interrupt. Connect this to a red led! Blink a special pattern to indicate this condition. Use time measurement that adjust to the different cpu clocks by reading from the clock source register?

• Booting pins working not clear