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An External Interrupt (Hardware Interrupt) – Introduction to Computer Control Methods
Your computer is a complex machine that can perform a multitude of tasks simultaneously. In order to effectively manage these tasks, it utilizes various control methods. One of the important control methods is known as an external interrupt, also referred to as a hardware interrupt. In this blog post, we will explore what an external interrupt is, how it works, and its significance in computer systems.
What is an External Interrupt?
An external interrupt is a mechanism that allows an external device or event to asynchronously interrupt the normal execution of a computer program. It provides a way for the computer to respond to external events in a timely and efficient manner. These events can be triggered by a variety of external sources, such as input from a keyboard, mouse, or other peripheral devices, or even an internal event like a timer reaching a specific value.
When an external interrupt occurs, it temporarily suspends the execution of the current program and transfers control to a specific interrupt service routine (ISR) or interrupt handler. The ISR is a piece of code that is designed to handle the specific interrupt and perform the necessary actions. Once the interrupt has been serviced, the program resumes its normal execution from where it left off.
How Does an External Interrupt Work?
To understand how an external interrupt works, let’s take a look at the process step by step:
1. External trigger: An external event, such as a button press or a signal from a peripheral device, sends a signal to the computer’s interrupt controller to indicate that an interrupt has occurred.
2. Interrupt request: The interrupt controller receives the signal and generates an interrupt request. It then sends this request to the processor or CPU.
3. Interrupt acknowledgment: The processor acknowledges the interrupt request and suspends the currently executing program.
4. Interrupt vector table: The processor consults the interrupt vector table, which is a data structure that maps interrupt numbers to the corresponding interrupt service routine addresses. It determines the appropriate ISR for the specific interrupt.
5. Interrupt service routine: The processor jumps to the address of the ISR associated with the interrupt and starts executing the ISR code.
6. Interrupt handling: The ISR performs the necessary actions to handle the interrupt. This can include reading data from input devices, updating variables or flags, or executing specific tasks related to the interrupt.
7. Return from interrupt: Once the ISR completes its execution, it signals the end of the interrupt handling and returns control back to the interrupted program, allowing it to resume its execution.
Significance of External Interrupts
External interrupts play a crucial role in computer systems for several reasons:
1. Real-time responsiveness: External interrupts enable the computer to respond rapidly to time-sensitive events, ensuring that critical tasks are handled promptly. This is especially important in embedded systems, where timely actions are essential.
2. Efficient resource utilization: By using external interrupts, the computer can rapidly switch between different tasks, allowing it to make efficient use of its processing power.
3. Simplified programming: External interrupts simplify the programming of systems that need to handle multiple concurrent events or tasks. Instead of continuously polling various input devices, the CPU can focus on executing the main program, relying on interrupts to handle external events.
In conclusion, external interrupts provide a valuable mechanism for computer systems to handle real-time events and efficiently manage concurrent tasks. By allowing external devices or events to interrupt the normal execution of a program, they enable timely and responsive control. Understanding and utilizing external interrupts effectively can greatly enhance the performance and reliability of computer-based systems.
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