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Interrupt Overview

Interrupt concept

  • Interrupt source: refers to the event that causes an interrupt or the source of an interrupt request.
  • Interrupt request: The request sent by the interrupt source to the CPU to suspend the currently executed task and handle the urgent task.
  • Breakpoint: When an interrupt occurs, the pause point of the interrupted program, that is, the place where the program is paused.

Interrupt priority and interrupt masking

Interrupt priority

  • Interrupt priority is to enable the system to respond to and handle all interrupt events in a timely manner. The system will classify interrupt sources into different levels according to the importance and urgency of the event.
  • In general, the order of interrupt priority from high to low is:
    • Hardware fault interrupt
    • Voluntary interrupt
    • Program interrupt
    • External interrupt
    • Input and output interrupt

Interrupt masking

  • Interrupt masking: In order to prevent low-priority interrupt event processing from interrupting high-priority interrupts, computer systems use interrupt masking technology. According to whether it can be masked, interrupts are divided into two categories:
  • Non-maskable interrupt: Once requested, the CPU must respond unconditionally.
  • Maskable interrupt: The CPU can choose to respond or ignore.

Interrupt processing method

  1. Sequential processing method:

    • In this method, when the processor is processing an interrupt, all new interrupt requests are masked until the current interrupt is processed and then check whether there is a new interrupt. If there is a new interrupt, continue to process it in sequence.

  2. Nested processing method:

    • When the system sets the interrupt priority, multiple interrupt requests of different priorities may arrive at the same time. The system will respond to the highest priority interrupt request first.
    • High-priority interrupt requests can preempt low-priority interrupt processing, similar to preemptive scheduling in process scheduling.

Interrupt processing process

  1. Wake up the blocked driver process:
    • When an interrupt occurs, the system may need to wake up some blocked processes to process resources or complete specific tasks.
  2. Protect the CPU environment of the interrupted process:
    • Save the state of the current process (such as register values) to ensure that the process can be restored after the interrupt processing is completed.
  3. Transfer to the corresponding device handler:
    • Jump to the corresponding device handler according to the interrupt source.
  4. Interrupt processing:
    • Execute the interrupt handler to handle related interrupt events.
  5. Restore the scene of the interrupted process:
    • After the interrupt processing is completed, restore the state of the original process and continue to execute the interrupted task.