Interrupts

Question 1

what is an interrupt

Answer 1

a signal to the CPU indicating that an event needs immediate attentoin, pausing the current program flow

Question 2

interupts can be either [1] or [2]

Answer 2

1 = hardware
2 = software

Question 3

what is an interupt service routine (ISR)

Answer 3

a small dedicated program that the CPU runs in response to an interrupt. after it is finished the control returns to the interruprted program

Question 4

at what point in the Fetch–Execute cycle are interrupts checked?

Answer 4

At the end of each cycle, before the next fetch phase begins.

Question 5

Outline the four main steps the CPU takes when handling an interrupt.

Answer 5

1. Save the volatile environment (PC, registers)
2. Jump to the ISR
3. Execute the ISR
4. Restore the saved state and resume the original program

Question 6

What is meant by the “volatile environment” and why must it be saved

Answer 6

The current contents of registers, the program counter (and sometimes stack pointer) that will change during the ISR; saving it lets the CPU restore and continue the original task correctly. |