An interrupt handler is a piece of software that is triggered by an interrupt ¹. Here's how it works ² ³:

*What is an interrupt?*
- An interrupt is an event that alters the normal execution flow of a program and can be generated by hardware devices or even by the CPU itself.

*How does an interrupt handler work?*
- When an interrupt occurs the current flow of execution is suspended and interrupt handler runs.
- After the interrupt handler runs the previous execution flow is resumed.

*Types of interrupts:*
- *Synchronous interrupts*: generated by executing an instruction and usually named exceptions.
- *Asynchronous interrupts*: external events generated by I/O devices and usually named interrupts.
- *Maskable*: can be ignored and signaled via INT pin.
- *Non-maskable*: cannot be ignored and signaled via NMI pin.

An interrupt handler, also known as an interrupt service routine (ISR), is a specialized routine in an operating system or device driver that responds to hardware interrupts generated by hardware devices or external events. Interrupt handlers are essential for handling asynchronous events and managing the interaction between hardware and software in a computer system. Here's how an interrupt handler works:

1. **Interrupt Generation**: When a hardware device or external event requires attention from the CPU, it generates an interrupt signal to the processor. Interrupts can be triggered by various events, such as I/O operations completing, timer expirations, hardware errors, or user input from devices like keyboards or mice.

2. **Interrupt Detection**: The CPU detects the interrupt signal and suspends the execution of the currently running program or process. This is known as interrupt processing or interrupt handling.

3. **Interrupt Acknowledgment**: The CPU acknowledges the interrupt signal and determines the source of the interrupt. Each interrupt is associated with a unique interrupt vector or identifier, which identifies the type and source of the interrupt.

4. **Interrupt Dispatching**: The CPU looks up the corresponding interrupt vector in the interrupt vector table (IVT) or interrupt descriptor table (IDT) to determine the address of the interrupt handler routine associated with the interrupt. This address points to the location in memory where the interrupt handler code is located.

5. **Interrupt Handling**: The CPU transfers control to the interrupt handler routine by executing a jump or branch instruction to the address of the interrupt handler code. The interrupt handler then begins execution, performing the necessary actions to handle the interrupt and respond to the event that triggered it.

6. **Interrupt Servicing**: The interrupt handler performs the required tasks to service the interrupt and respond to the event. This may include reading or writing data to/from the hardware device, updating status registers, clearing interrupt flags, or performing error handling and recovery procedures.

7. **Interrupt Completion**: Once the interrupt handler has completed its tasks, control returns to the interrupted program or process. The CPU resumes execution of the program from the point where it was interrupted, allowing it to continue its normal operation.

8. **Interrupt Prioritization**: In systems with multiple interrupts, interrupt handlers may be prioritized based on the urgency or importance of the events they handle. Higher-priority interrupts may preempt lower-priority interrupts, ensuring that critical tasks are serviced promptly.

Overall, interrupt handlers play a critical role in handling hardware interrupts and managing the interaction between hardware devices and software in a computer system. They allow the CPU to respond to asynchronous events efficiently, ensuring timely and effective processing of interrupts while maintaining system stability and responsiveness.