Book Image

Mastering Embedded Linux Programming

By : Chris Simmonds
Book Image

Mastering Embedded Linux Programming

By: Chris Simmonds

Overview of this book

Mastering Embedded Linux Programming takes you through the product cycle and gives you an in-depth description of the components and options that are available at each stage. You will begin by learning about toolchains, bootloaders, the Linux kernel, and how to configure a root filesystem to create a basic working device. You will then learn how to use the two most commonly used build systems, Buildroot and Yocto, to speed up and simplify the development process. Building on this solid base, the next section considers how to make best use of raw NAND/NOR flash memory and managed flash eMMC chips, including mechanisms for increasing the lifetime of the devices and to perform reliable in-field updates. Next, you need to consider what techniques are best suited to writing applications for your device. We will then see how functions are split between processes and the usage of POSIX threads, which have a big impact on the responsiveness and performance of the final device The closing sections look at the techniques available to developers for profiling and tracing applications and kernel code using perf and ftrace.
Table of Contents (22 chapters)
Mastering Embedded Linux Programming
Credits
Foreword
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

High resolution timers


Timer resolution is important if you have precise timing requirements which is typical for real-time applications. The default timer in Linux is a clock that runs at a configurable rate, typically 100 Hz for embedded systems and 250 Hz for servers and desktops. The interval between two timer ticks is known as a jiffy and, in the examples given above, is 10 milliseconds on an embedded SoC and four milliseconds on a server.

Linux gained more accurate timers from the real-time kernel project in version 2.6.18 and now they are available on all platforms, providing that there is a high resolution timer source and device driver for it – which is almost always the case. You need to configure the kernel with CONFIG_HIGH_RES_TIMERS=y.

With this enabled, all the kernel and user space clocks will be accurate down to the granularity of the underlying hardware. Finding the actual clock granularity is difficult. The obvious answer is the value provided by clock_getres(2) but that...