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Interrupts

Interrupts. Signal 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. Interrupt Terminology.

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Interrupts

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  1. Interrupts • Signal 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 http://sites.google.com/site/computing9691/

  2. Interrupt Terminology • In 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 http://sites.google.com/site/computing9691/

  3. Servicing an Interrupt • When 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. http://sites.google.com/site/computing9691/

  4. Servicing an Interrupt http://sites.google.com/site/computing9691/

  5. Use of Interrupts • Interrupts 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 • Softwareinterrupts http://sites.google.com/site/computing9691/

  6. Multiple Interrupts • Identifying 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 http://sites.google.com/site/computing9691/

  7. Vectored Interrupts http://sites.google.com/site/computing9691/

  8. Polled Interrupts http://sites.google.com/site/computing9691/

  9. Multiple Interrupts Example http://sites.google.com/site/computing9691/

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