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
About the Author
About the Reviewers

Measuring scheduling latencies

All the configuration and tuning you may do will be pointless if you cannot show that your device meets the deadlines. You will need your own benchmarks for the final testing but I will describe here two important measurement tools: cyclictest and Ftrace.


cyclictest was originally written by Thomas Gleixner and is now available on most platforms in a package named rt-tests. If you are using the Yocto Project, you can create a target image that includes rt-tests by building the real-time image recipe like this:

$ bitbake core-image-rt

If you are using Buildroot, you need to add the package, BR2_PACKAGE_RT_TESTS in the menu Target packages | Debugging, profiling and benchmark | rt-tests.

cyclictest measures scheduling latencies by comparing the actual time taken for a sleep to the requested time. If there was no latency they would be the same and the reported latency would be zero. cyclictest assumes a timer resolution of less than one microsecond.