I/O

Data registers: contain data that needs to be read or written, e.g., data received from the UART.

Status registers: contain device information, e.g., health, data received or successfully written, and configuration.

I/O Access

There are two major mechanisms to access data from I/O devices:

• Polling: synchronous. Also known as busy waiting. Polling blocks other activities, high power consumption, predictable timing, and high throughput.

• Interrupts: asyncrhonous operation. The CPU can do other activities while waiting for data to complete, non-linear control flow (source of bugs), requires prioritization, and bugs are hard to reproduce.