An interrupt service routine, or ISR, is code associated with handling an interrupt condition. An interrupt can temporarily change the normal flow of execution so that an event is addressed. The details depend on the processor, operating environment and device.
Distinguish the event from the handler
The interrupt is the condition or request; the ISR is the routine used to handle it. A peripheral event is one possible source, but not every platform uses identical names or mechanisms. State the architecture or environment you are discussing rather than treating a general description as a universal implementation rule.
Explain the change in execution
Handling an interrupt may require preserving relevant execution state, entering a handler and later resuming appropriate work. The hardware and software divide these responsibilities differently across systems. Use the reference manual prescribed by the module. Avoid importing a register sequence from another processor just because both use the word “interrupt”.
Connect the ISR to the system’s needs
Explain what event the handler responds to and what information must be processed or recorded. Consider timing and interaction with other work at the level required by the assignment. A long general description of the processor may not answer a question about the specific role of the handler.
Discuss constraints without universal claims
Restrictions on operations, priorities and shared data depend on the environment. Identify the relevant documentation and distinguish an implementation requirement from a general design preference. If the handler communicates with ordinary code, explain the mechanism expected by the course and the reason it is suitable.
Demonstrate understanding in coursework
Use a simple labelled sequence or trace, identify the triggering event and explain how control returns or work is deferred. Keep a proposed implementation separate from verified behaviour. Testing should use the authorised development environment. A concise account tied to the actual architecture is stronger than a copied example with incompatible assumptions.
Sources and further reading
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