> For the complete documentation index, see [llms.txt](https://lagnos.gitbook.io/linux-kernel-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://lagnos.gitbook.io/linux-kernel-notes/concepts/interrupts.md).

# interrupts

* [Introduction](#introduction)
* [Types of Interrupts](#types-of-interrupts)
* [Interrupt Controllers](#interrupt-controllers)
* [Interrupt Flow](#interrupt-flow)
* [Top Halves](#top-halves)
* [Bottom Halves](#bottom-halves)

### Introduction

* event that alters the normal flow of a program
* can be generated by hardware devices or by the CPU itself
* physically produced by **electronic signals** generated by hardware and directed to the input pins on an `interrupt controller`.

### Types of Interrupts

* Based on the source of interrupt :
  * Synchronous → Generated by executing an instruction (Eg : [syscalls](/linux-kernel-notes/concepts/syscalls/syscalls.md), Divide by Zero)
  * Asynchronous → Based on external event (Eg : Key presses on keyboard)
* Based on ability to temporarily disable :
  * Maskable → can be ignored; it is signaled via **INT** pin
  * Non-Maskable → cannot be ignored ; it is signaled via **NMI** pin

### Interrupt Controllers

> An interrupt controller is a simple chip that multiplexes multiple interrupt lines into a single interrupt line on the processor.

* when an interrupt occurs, the current flow of execution is stopped and the **interrupt handler** runs (unless interrupts are disabled for **critical sections**)
* Each interrupt has a unique value assigned to it so that interrupts from 2 different devices can be differentiated. These values are called `Interrupt Request (IRQ) lines`.

### Interrupt Flow

TODO: add flow excali svg here

### Top Halves

### Bottom Halves

TODO: add backlinks here

Their are 4 ways to defer work in Bottom Half

1. softirq
2. tasklet
3. [workqueue](/linux-kernel-notes/core-apis/core-utilities/workqueue.md) (replacement of task queues)
4. kernel Timer