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Interrupt Service Routine

An ISR is the function the hardware calls when its interrupt fires, preempting the main program, so it must be short, avoid blocking calls, and exchange data with the main loop only through volatile variables read atomically. Work beyond a few instructions belongs in the main loop, signalled by a flag the ISR sets.

Questions this Concept answers

Why is an interrupt service routine expected to do the smallest possible amount of work?

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How CPU Interrupts Work in Computer Architecture

A CPU interrupt is a signal that halts a processor's normal instruction flow to demand immediate attention for an event, replacing inefficient polling (repeatedly querying device state) with an event…