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INTERRUPT TYPES SHOWN WITH DECREASING PRIORITY ORDER • Reset • Internal interrupts and exceptions

INTERRUPT TYPES SHOWN WITH DECREASING PRIORITY ORDER • Reset • Internal interrupts and exceptions • Software interrupt • Nonmaskable interrupt • Hardware interrupt

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INTERRUPT TYPES SHOWN WITH DECREASING PRIORITY ORDER • Reset • Internal interrupts and exceptions

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  8. INTERRUPT TYPES SHOWN WITH DECREASING PRIORITY ORDER • Reset • Internal interrupts and exceptions • Software interrupt • Nonmaskable interrupt • Hardware interrupt All the interrupts are serviced on priority basis. The higher priority interrupt is served first and an active lower priority interrupt service is interrupted by a higher priority one. Lower priority interrupts will have to wait until their turns come. The section of program to which the control is passed called Interruptserviceroutine (e.g. printer driver) 2014年10月21日8

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  10. Example • At what address should vector 50, CS50, and IP50 be stored in memory? • Each vector requires four bytes of memory • Address = 50 x 4 = 200 • Converting to binary – 200 = 1100 1000b – Address = C8h • IP50 is stored in 00C8h • CS50 is stored in 00CAh 2014年10月21日10

  11. Interrupt instructions • Interrupt enable flag (IF) causes external interrupts to be enabled. • INT n initiates a vectored call of a subroutine. • INTO instruction should be used after each arithmethic instruction where there is a possibility of an overflow. • HLT waits for an interrupt to occur. • WAIT waits for TEST input to go high. 2014年10月21日11

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  18. Resident Programs • Usually non-resident program is a file, loaded from disk by DOS. Termination of such program is the passing control back to DOS. DOS frees all memory, allocated for and by this program, and stays idle to execute next program. • Resident program passes control to DOS at the end of its execution, but leaves itself in memory whole or partially. • Such way of program termination was called TSR - Terminate-and-Stay-Resident. So resident programs often called by this abbreviations - TSR. • TSR stays in memory to have some control over the processes. Usually, TSRs takes INTerrupt vectors to its code, so, when interrupt occurs, vector directs execution to TSR code. • For example, TSR can watch keypresses to steal password, INT 13h sectors operations to substitute info, INT 21h to watch and dispatch file operations and so on. 2014年10月21日18

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