GPIO

GPIOx->BSRR Write only operation to set or reset register. Must use or to not overwrite unwanted bits. Atomic

GPIOx->IDR Read register

RCC->AHB1ENR Enable GPIO clock enable

GPIOx->MODER Set GPIO mode

GPIOx->PUPDR Set PULLUP/PULLDOWN/NOPULL on pin

GPIOx->OTYPER Set GPIO output type register

GPIOx->ODR Set GPIO output data register pin to 1 or 0. Read/Write operation. Not atomic