What is an Interrupt?
An interrupt is a mechanism that allows the normal sequence of program execution to be temporarily halted and transferred to a specific routine known as an interrupt service routine (ISR) or interrupt handler. Interrupts are events that require immediate attention from the processor.
Why are Interrupts Used?
1. Handling External Events:
- Interrupts are used to handle external events or signals that occur outside the normal flow of program execution. Examples include hardware signals, I/O completion, or timer events.
2. Real-Time Responsiveness:
- Interrupts provide a way for a computer system to respond promptly to external events, making it suitable for real-time systems.
3. Efficient Resource Utilization:
- Interrupts allow the processor to perform other tasks while waiting for external events, improving overall system efficiency.
Different Kinds of Interrupts:
1. Hardware Interrupts:
- Generated by external hardware devices to request attention from the processor. Examples include I/O interrupts, timer interrupts, and error interrupts.
2. Software Interrupts:
- Invoked by software instructions to request specific services or operations. Often used for system calls or to signal specific events.
3. Maskable Interrupts:
- Interrupts that can be temporarily disabled (masked) by the processor. The decision to mask or unmask these interrupts depends on the current state of the system.
4. Non-Maskable Interrupts (NMI):
- Interrupts that cannot be disabled or masked by the processor. They usually indicate critical system errors that require immediate attention.
Process of Interrupt Processing:
1. **Interrupt Request (IRQ):**
- An external event occurs, and an interrupt request is generated. This could be a hardware device signaling completion, a timer reaching zero, or other events.
2. **Interrupt Controller:**
- The interrupt controller prioritizes and manages multiple interrupt requests if present. It informs the processor about the highest-priority pending interrupt.
3. Interrupt Handling:
- The processor saves the current state of the program (registers, program counter) and transfers control to the appropriate interrupt service routine (ISR).
4. Interrupt Service Routine (ISR):
- The ISR is a specific routine designed to handle the interrupt. It performs the necessary tasks associated with the interrupt, such as updating data or responding to a hardware event.
5. Context Switch:
- The processor may need to switch between the interrupted task and the ISR. This involves saving the interrupted task's context and restoring it after the ISR execution.
6. **Return from Interrupt (RTI):
- After the ISR completes its tasks, a return-from-interrupt instruction is executed. This restores the saved context, allowing the interrupted task to resume.
Interrupts are crucial for efficient multitasking, real-time processing, and handling diverse events in computer systems. They enhance the responsiveness and flexibility of the system architecture.
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