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Mastering Embedded Linux Programming

You're reading from   Mastering Embedded Linux Programming Unleash the full potential of Embedded Linux with Linux 4.9 and Yocto Project 2.2 (Morty) Updates

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Product type Paperback
Published in Jun 2017
Publisher Packt
ISBN-13 9781787283282
Length 478 pages
Edition 2nd Edition
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Author (1):
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Mr. Chris Simmonds Mr. Chris Simmonds
Author Profile Icon Mr. Chris Simmonds
Mr. Chris Simmonds
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Table of Contents (17) Chapters Close

Preface 1. Starting Out FREE CHAPTER 2. Learning About Toolchains 3. All About Bootloaders 4. Configuring and Building the Kernel 5. Building a Root Filesystem 6. Selecting a Build System 7. Creating a Storage Strategy 8. Updating Software in the Field 9. Interfacing with Device Drivers 10. Starting Up – The init Program 11. Managing Power 12. Learning About Processes and Threads 13. Managing Memory 14. Debugging with GDB 15. Profiling and Tracing 16. Real-Time Programming

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...

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