I/O//MMIO

- Memory-mapped I/O — hardware registers mapped into the CPU's address space so they look like ordinary RAM locations.

Memory-mapped I/O — hardware registers mapped into the CPU's address space so they look like ordinary RAM locations.

A write to 0x4000_1000 might toggle a GPIO pin; a read from 0x4001_0004 might fetch an ADC sample.

MCU programming is largely MMIO.

STM32 and ESP32 SDKs provide register-level abstractions over MMIO addresses.