Book Image

Linux Device Drivers Development

By : John Madieu
Book Image

Linux Device Drivers Development

By: John Madieu

Overview of this book

Linux kernel is a complex, portable, modular and widely used piece of software, running on around 80% of servers and embedded systems in more than half of devices throughout the World. Device drivers play a critical role in how well a Linux system performs. As Linux has turned out to be one of the most popular operating systems used, the interest in developing proprietary device drivers is also increasing steadily. This book will initially help you understand the basics of drivers as well as prepare for the long journey through the Linux Kernel. This book then covers drivers development based on various Linux subsystems such as memory management, PWM, RTC, IIO, IRQ management, and so on. The book also offers a practical approach on direct memory access and network device drivers. By the end of this book, you will be comfortable with the concept of device driver development and will be in a position to write any device driver from scratch using the latest kernel version (v4.13 at the time of writing this book).
Table of Contents (23 chapters)
Free Chapter
1
Introduction to Kernel Development

PWM Drivers

Pulse Wide Modulation (PWM) operates like a switch that constantly cycles on and off. It is a hardware feature used to control servomotors, for voltage regulation and so on. The most well-known applications of PWM are:

  • Motor speed control
  • Light dimming
  • Voltage regulation

Now, let's introduce PWM with a simple diagram:

The preceding figure describes a complete PWM cycle, introducing some terms we need to clarify prior to getting deeper into the kernel PWM framework:

  • Ton: This is the duration during which the signal is high.
  • Toff: This is the duration during which the signal is low.
  • Period: This is the duration of a complete PWM cycle. It represents the sum of Ton and Toff of the PWM signal.
  • Duty cycle: It is represented as a percentage of the time signal that remains on during the period of the PWM signal.

Different formulas are detailed as follows:

  • PWM period...