Interrupts are a fundamental mechanism in computer systems that allow the CPU (Central Processing Unit) to temporarily pause its current execution to handle an external event or request. These external events, called interrupt requests (IRQs), can come from various sources, such as hardware devices, timers, or software.
Here’s an overview of interrupts and their significance in computer systems:
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Interrupt Requests (IRQs): IRQs are signals generated by external devices or events that need immediate attention or servicing by the CPU. These events can include hardware-related events like keyboard input, mouse movement, disk I/O completion, or software-related events like system calls or exceptions.
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Interrupt Controller: In modern computer systems, an interrupt controller manages and prioritizes IRQs. It acts as an intermediary between the external devices generating interrupts and the CPU. The interrupt controller determines which interrupt to service first based on priority and can mask (disable) or unmask (enable) specific interrupts.
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Interrupt Service Routine (ISR): When an interrupt is triggered, the CPU temporarily suspends its current execution and transfers control to a designated piece of code called an Interrupt Service Routine (ISR) or interrupt handler. The ISR is responsible for handling the specific interrupt request. Once the ISR completes its task, control returns to the previously executing program.
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Context Switching: When an interrupt occurs, the CPU performs a context switch. This involves saving the current program’s state (registers, program counter, etc.), loading the state required to execute the ISR, and then resuming execution of the ISR. After the ISR completes, the CPU performs another context switch to return to the interrupted program.
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Priority and Nesting: Interrupts may have different priorities, and the interrupt controller ensures that higher-priority interrupts are serviced before lower-priority ones. In some systems, interrupt nesting is supported, allowing an ISR to be interrupted by a higher-priority interrupt.
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Masking and Disabling Interrupts: Some interrupts can be temporarily masked or disabled to prevent their handling. This can be useful in critical sections of code where interrupts might disrupt the program’s flow.
Interrupts are essential for real-time and multitasking operating systems, as they allow the CPU to efficiently manage multiple activities concurrently. They are used in a wide range of applications, including hardware device management, timekeeping, communication, and user input. Handling interrupts efficiently is crucial for system performance and responsiveness.
Conclusion: interrupts are mechanisms that allow external events or requests to momentarily suspend the CPU’s execution and execute specific code (ISRs) to handle those events. They play a critical role in the interaction between hardware devices and software, enabling responsive and multitasking computer systems.