94.574 Elements of Computer Systems

SCE 574

107

Why Software Interrupts?

äHardware interrupts are used to handle communication to/from peripheral devices

äHardware interrupt occurs when an external device sends a signal to the 8088’s interrupt request line along with an interrupt number n on the 8088 data lines. The 8088 then:

ä1. Stops whatever is being done

ä2. Jumps to a subroutine n to handle the data going to/from the device

ä3. Returns to whatever was being done

äSoftware interrupts

äCan be used to test the implementation of the interrupt handling routines

äInterrupt table approach is useful because

äIndirection given by the interrupt vector means we only need to specify the address of the routine in the vector, can reference the routine using n

äCan lead to problems if 2 devices expect to use same n