General Sequence Followed When Interrupts Occur By An External Device
- Interrupt request(IRQ) signal is sent by the device to the processor.
- If the interrupt line is enabled the following sequence of events occur in the system, else the interrupt is ignored. The processor completes its present instruction (if any) and pays attention to the IRQ.
- It stores the address of the next location and content of status register to the stack
- It informs the device that its request has been granted and in response the device de-activates its IRQ.
- Using some suitable technique the processor loads its program counter(PC) with address of the ISR.
- With return statement occurring at the end of the ISR all stored content is loaded back into the respective registers and the processor resumes its suspended program*.
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- In preemptive scheduled operating systems the processor's control is given to process scheduler instead of the interrupted process.
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