Question

With respect to bus request interrupts: What must be allowed to complete before the interrupts is serviced? What resources (CPU, buses, memory, etc..) is the ISR expected to use? What is the ISR typically expected to do? Is the interrupted task expected to resume after the ISR runs? What must be saved before the ISR is run?

Answer 1

a)The instruction which is executing gets executed and saves the address of the next instruction (PC) on the stack whenever the interrupt is serviced.

b)ISR is expected to use memory to store the address of the interrupt service routine. That memory is called interrupt vector table.

c) interrupt service routine (ISR), is a callback subroutine in an operating system or device driver whose execution is triggered by the reception of an interrupt

Step in executing an Interrupt:

1) It finish the instruction it is executing and saves the address of the next instruction (PC) on the stack.

2) It also saves the current status of all the interrupt internally.

3) It Jumps to a fixed location in memory called the interrupt vector table that holds the address of the interrupt service routine.

4) The microcontroller gets the address of the ISR from the interrupt vector and jumps to it. It starts to execute the interrupt service subroutine until it reaches the last instruction of the subroutine.

5) Upon executing the RETI instruction ,the microcontroller returns to the Place where it was interrupt.

d)yes the interrupted task resumes once the ISR runs successfully.

e)the address of the next instruction which needs to be executed gets saved before ISR runs.