Q. Perform on occurrence of an interrupt?

Determining these requirements let's work out steps that CPU should perform on occurrence of an interrupt.

• The CPU should find out source of interrupt as this will decide which interrupt service routine is to be executed.
• The CPU then obtains the address of interrupt service routine which are stored in memory (in general).
• What occurs to program the CPU was executing before interrupt? This program requires to be interrupted till CPU executes ISR (Interrupt service program). Do we need to do something for this specific program? Well context of this program is to be kept.
• Ultimately CPU executes interrupt service routine till completion of routine. A RETURN statement signifies the end of this routine. Later the control is passed back to interrupted program.