interrupts

• Introduction

• Types of Interrupts

• Interrupt Controllers

• Interrupt Flow

• Top 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, 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 (replacement of task queues)
4. kernel Timer