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

Filesystems for flash memory


There are several challenges when making efficient use of flash memory for mass storage: the mismatch between the size of an erase block and a disk sector, the limited number of erase cycles per erase block, and the need for bad block handling on NAND chips. These differences are resolved by a Flash Translation Layer globally, or FTL.

Flash translation layers

A flash translation layer has the following features:

  • Sub allocation: Filesystems work best with a small allocation unit, traditionally a 512-byte sector. This is much smaller than a flash erase block of 128 KiB or more. Therefore erase blocks have to be sub-divided into smaller units to avoid wasting large amounts of space.

  • Garbage collection: A consequence of sub-allocation is that an erase block will contain a mixture of good data and stale data after the filesystem has been in use for a while. Since we can only free up whole erase blocks, the only way to reclaim the free space is to coalesce the good data...