Interrupt Service Routine (ISR)
Computer Science: OCR A Level, topic 2.1.7
Interrupt Service Routine (ISR)
An interrupt service routine is a set of instructions that need to be done as part of an interrupt.
ISR
- An interrupt service routine is a set of instructions that need to be done as part of an interrupt.
- When an interrupt service routine has been completed, the CPU will go back to the set of instructions it was doing before.
Process
- As an interrupt arrives at the CPU it comes with a flag to indicate the priority of the interrupt.
- This interrupt could be higher importance than the set of instructions it is currently working.
- The interrupt pushes the current instruction and all the contents of the registers in the CPU to a stack.
Process cont.
- The CPU will then complete the interrupt service routine and then load the registers back in from the stack and continue where it left off.
- At the end of each fetch, decode, execute cycle, the CPU checks for interrupts and their priorities before continuing on.
Test yourself on Interrupt Service Routine (ISR)
At what point in the fetch, decode, execute cycle does the CPU check for interrupts and their priorities before continuing on?