[flyingcircus3]

I found that AVR devices are more approachable microcontrollers for learning the concepts of setting up and using peripherals at the register level, and studying the part's datasheet. They are so much simpler than ARM chips, with far fewer peripherals and registers.

I think a good approach to this is to take working examples, look up the used registers in the datasheet, understand why setting up the peripherals that particular way accomplishes the goal of the example, and then start experimenting with changes to those registers.