InterruptsSignal that causes the CPU to alter its

normal flow on instruction execution◦ frees CPU from waiting for events◦ provides control for external input

Examples◦ unexpected input◦ abnormal situation◦ illegal instructions◦ multitasking, multiprocessing

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Slide 1

Interrupt TerminologyIn understanding the concept of

interrupts, there are a few commonly used terms:-◦ Interrupt lines (hardware)◦ Interrupt request◦ Interrupt handlers

Program that services the interrupt Also known as an interrupt routine

◦ Process Control Block (PCB) Located in a part of memory known as the stack

area All registers of a program are saved here before

control is transferred to the interrupt handler

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Slide 2

Servicing an InterruptWhen an interrupt occurs, it must

be serviced.Servicing the interrupt involves:-

◦suspending the program in progress.◦save pertinent information including

last instruction executed and data values in registers in the PCB (process control block).

◦branch to the interrupt handler.

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Slide 3

Servicing an Interrupt

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Use of InterruptsInterrupts are such powerful

mechanisms that they are used widely, such as:-◦ Notifying that an external event has

occurred real-time or time-sensitive

◦ Signalling completion printer ready or buffer full

◦ Allocating CPU time time sharing

◦ Indicating abnormal event (CPU originates for notification and recovery) illegal operation, hardware error

◦ Software interruptshttp://sites.google.com/site/computing9691/

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Multiple InterruptsIdentifying devices

◦Polling (checking for input in rotation)

◦Vectored interrupts (include address of interrupting device)

Interrupt priorities◦Loss of data vs. task completion

Maskable (disabled) interrupts

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Vectored Interrupts

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Slide 7

Polled Interrupts

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Slide 8

Multiple Interrupts Example

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