Lec18_interrupt_

Lec18_interrupt_ - ECE 212 Digital Circuits II Monday 7...

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1 ECE 212 Digital Circuits II Monday, 7 April 2008 HW Set 18: Problem 1 Jeff V. Problem 2 James W. Problem 3 Nick W. Problem 4 Derek A. Today's Goals To understand the important features of an interrupt system. To understand the 6812 interrupt system.
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2 main: . . . . . . IR: . . . . . rti Interrupt Routine IR Interrupt Routine An interrupt routine is like a subroutine . . . but it is called by an external device. main: . . . bsr SR . . Subroutine SR SR: . . . . . rts NO bsr instruction. Return from Subroutine Return from Interrupt Interrupt Issues (1/2) No bsr instruction in main . main does NOT know when the interrupt strikes. [ The interrupt routine works independently of main . ] [ The interrupt routine is asynchronous to main . (Subroutines are synchronous to the calling program.) ] Exactly when can main be interrupted? The interrupt routine must be transparent to main. main must NOT be screwed up by the interrupt routine.
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3 Interrupt Issues (2/2) How does an external device call an interrupt routine? How does the processor know where the interrupt routine is located in memory? How many elephants can you fit in a VW Beetle? main is doing something very important. Can we prevent it from being interrupted? The processor is currently in an interrupt routine. Can it be interrupted by a second device? Why rti instead of rts at the end of the routine? Why use an interrupt routine in the first place ??? When can main be interrupted? Program execution: Each instruction cycle spans a number clock periods. An interrupting device can strike at any time. The processor can be interrupted only at the end of an instruction cycle.
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This note was uploaded on 04/17/2008 for the course ECE 212 taught by Professor Greco during the Spring '08 term at Lafayette.

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Lec18_interrupt_ - ECE 212 Digital Circuits II Monday 7...

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