Interrupts Vs Polling

Polling checks for data repeatedly. Interrupts react when a device signals that data is available.

Mechanism	Best use	Trade-off
Polling	simple tests, predictable short waits	wastes CPU when events are rare
Interrupts	normal interactive input	needs event-loop structure

Keyboard events are sporadic, so interrupts are usually a better fit. Polling is still useful to understand the controller and to build small deterministic experiments.

In the interrupt version, the program can wait for messages from the runtime and handle keyboard input only when the controller has something to report. In the polling version, the program repeatedly checks the status register and decides whether to try a read. Both versions exercise the same controller rules. The difference is how the program decides when to ask for data.

Timeout Discipline

Polling loops need limits. A loop that waits forever for a key can hang a test, a project demo, or a grading run.

Timer-driven limits are especially useful because they make the behavior observable. A function that says "wait until ESC is released or until N seconds of idle time have passed" has a precise contract. A function that says "wait for some input" can easily become impossible to test.

TIP

Poll with a clear maximum number of attempts or a timer-driven timeout. Then return an error the caller can handle.