Computer Science – Software | e-Consult

Interrupts are signals that cause the CPU to temporarily stop its current task and execute a specific routine, known as an interrupt handler. Their primary role is to allow the system to respond to events, both internal (e.g., a device requesting attention) and external (e.g., a user pressing a key). Without interrupts, the CPU would have to constantly poll devices to check for activity, which is inefficient.

The handling of an interrupt typically involves the following steps:

• Interrupt Request (IRQ): A device sends an IRQ signal to the CPU.
• Interrupt Recognition: The CPU checks if it is currently in a critical section (e.g., performing a time-critical operation) and whether interrupts are enabled.
• Interrupt Disable (Optional): If the interrupt is not to be serviced immediately, the CPU may disable interrupts temporarily.
• Save Context: The CPU saves the current state of the program (registers, program counter) onto the stack. This allows the CPU to resume the interrupted program later.
• Interrupt Vector: The CPU uses the IRQ signal to determine the address of the appropriate interrupt handler in the interrupt vector table.
• Jump to Handler: The CPU jumps to the address specified in the interrupt vector table, executing the interrupt handler.
• Service the Request: The interrupt handler performs the necessary actions to respond to the event that caused the interrupt (e.g., reading data from a device).
• Restore Context: The CPU restores the saved context from the stack.
• Interrupt Enable: The CPU re-enables interrupts (if they were disabled).
• Return to Program: The CPU returns to the point where it was interrupted and resumes execution.