What is an interrupt service routine?

An interrupt service routine is the section of operating system code that deals with one kind of interrupt. The routine executes in kernel mode.

What is an interrupt vector?

An interrupt vector is the stored address of the service routine for one particular interrupt. The vector table holds one entry for each type of interrupt.

Why are the register contents saved on a stack rather than in fixed locations?

A stack allows one interrupt to be serviced while another is already being handled. The most recently saved state is always restored first.

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Interrupts, Memory Management and Scheduling

Interrupt handling and the interrupt service routine

3 things to know
Component 2

Overview

What happens immediately after the processor accepts an interrupt, interrupt service routine and interrupt vector.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Process

When in the fetch-execute cycle does the processor test for an interrupt?

Key term

Why is the current instruction completed before an interrupt is serviced?

Process

Describe what happens immediately after the processor accepts an interrupt.

Questions from this subtopic

Each one with the model answer underneath.

1
When in the fetch-execute cycle does the processor test for an interrupt?
Model answer
The processor checks the interrupt register at the end of each fetch-execute cycle. The instruction in progress is always completed first.
2
Why is the current instruction completed before an interrupt is serviced?
Model answer
A half-executed instruction would leave the registers and memory in an inconsistent state. Completion keeps the interrupted process restartable.
3
Describe what happens immediately after the processor accepts an interrupt.
Model answer
The contents of the program counter and the other registers are copied onto a stack. The address of the correct service routine is then loaded into the program counter.
4
What is an interrupt service routine?
Model answer
An interrupt service routine is the section of operating system code that deals with one kind of interrupt. The routine executes in kernel mode.
5
What is an interrupt vector?
Model answer
An interrupt vector is the stored address of the service routine for one particular interrupt. The vector table holds one entry for each type of interrupt.
6
Why are the register contents saved on a stack rather than in fixed locations?
Model answer
A stack allows one interrupt to be serviced while another is already being handled. The most recently saved state is always restored first.

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