Book Image

Mastering Embedded Linux Programming - Third Edition

By : Frank Vasquez, Chris Simmonds
5 (3)
Book Image

Mastering Embedded Linux Programming - Third Edition

5 (3)
By: Frank Vasquez, Chris Simmonds

Overview of this book

If you’re looking for a book that will demystify embedded Linux, then you’ve come to the right place. Mastering Embedded Linux Programming is a fully comprehensive guide that can serve both as means to learn new things or as a handy reference. The first few chapters of this book will break down the fundamental elements that underpin all embedded Linux projects: the toolchain, the bootloader, the kernel, and the root filesystem. After that, you will learn how to create each of these elements from scratch and automate the process using Buildroot and the Yocto Project. As you progress, the book will show you how to implement an effective storage strategy for flash memory chips and install updates to a device remotely once it’s deployed. You’ll also learn about the key aspects of writing code for embedded Linux, such as how to access hardware from apps, the implications of writing multi-threaded code, and techniques to manage memory in an efficient way. The final chapters demonstrate how to debug your code, whether it resides in apps or in the Linux kernel itself. You’ll also cover the different tracers and profilers that are available for Linux so that you can quickly pinpoint any performance bottlenecks in your system. By the end of this Linux book, you’ll be able to create efficient and secure embedded devices using Linux.
Table of Contents (27 chapters)
1
Section 1: Elements of Embedded Linux
10
Section 2: System Architecture and Design Decisions
18
Section 3: Writing Embedded Applications
22
Section 4: Debugging and Optimizing Performance

Powering down peripherals

The discussion up to now has been about CPUs and how to reduce power consumption when they are running or idling. Now it is time to focus on other parts of the system peripherals and see whether we can achieve power savings here.

In the Linux kernel, this is managed by the runtime power management system or runtime pm for short. It works with drivers that support runtime pm, shutting down those that are not in use and waking them again when they are next needed. It is dynamic and should be transparent to user space. It is up to the device driver to implement the management of the hardware, but typically, it would include turning off the clock to the subsystem, also known as clock gating, and turning off core circuitry where possible.

The runtime power management is exposed via a sysfs interface. Each device has
a subdirectory named power, in which you will find these files:

  • control: This allows user space to determine whether runtime pm is used...