AQA 7517 4.7.3.6: Interrupts
The free BugBot lesson that teach this point, a robot to try it on, and the past-paper questions that test it.
What it covers
A processor runs one instruction after another. So how does it notice a key being pressed, a network packet arriving or a battery running flat, in the middle of whatever program it is running? It could keep checking every device, but that wastes almost all its time. Instead, devices interrupt it. This lesson follows an interrupt through the fetch-decode-execute cycle, and shows why the processor's registers must be saved on a stack first.
- What an interrupt is
- Polling or interrupts?
- Interrupts and the fetch-decode-execute cycle
- Why save the registers?
- Priorities and nesting
- A timer interrupt for a robot
Or do it in the simulator, with tasks that mark themselves
Lessons that teach it
- A9.7 Interrupts Computer architecture
Sources of interrupts, polling, the check at the end of each cycle, saving the volatile environment on a stack, and priorities.
Try it on a robot
The task from A9.7 Interrupts, running here. Change the program and press Run.
The specification is AQA's own document; this page says which of our lessons teach point 4.7.3.6 and is not endorsed by the board.