Handling Multiple Devices

Interrupt Priority

•   Continue to accept interrupt requests from higher priority components
•   Disable interrupts from component at the same level priority or lower
•   At the time of execution of interrupt-service routine
•   Privileged instructions executed in the supervisor mode

Controlling device requests

•   Interrupt-enable

KEN, DEN

Implementation of interrupt priory by using individual interrupt-request and acknowledge lines

Polled interrupts: Priority decided by the order in which processor polls the component (polls their status registers) vectored interrupts: Priority determined by the order in which processor tells component toput its code on the address lines (order of connection in the chain)

(a)   Daisy chain

Daisy chaining of INTA: If device has not requested any service, passes the INTA signal to next device if necessitate service, does not pass the INTA, puts its code on the address lines Polled