The Cortex-M Memory Map
A microcontroller has one 4 GB address space and everything lives in it: flash, RAM, every peripheral register, the interrupt controller, the debug hardware. There is no MMU, so what you write in a pointer is the physical address the bus sees. That is the simplification that makes bare-metal firmware tractable — and it means the layout of that space is not a vendor's private business but part of the architecture you program against.