.System Monitoring
4. Development Tools
A Practical Project Workspace
GNU Cross-Platform Development Toolchain
C Library Alternatives
Java
Perl
Python
Other Programming Languages
Eclipse: An Integrated Development Environment
Terminal Emulators
5. Kernel Considerations
Selecting a Kernel
Configuring the Kernel
Compiling the Kernel
Installing the Kernel
In the Field
6. Root Filesystem Content
Basic Root Filesystem Structure
Libraries
Kernel Modules
Kernel Images
Device Files
Main System Applications
Custom Applications
System Initialization
7. Storage Device Manipulation ..
MTD-Supported Devices
Disk Devices
To Swap or Not To Swap
8. Root Filesystem Setup
Filesystem Types for Embedded Devices
Writing a Filesystem Image to Flash Using an NFS-Mounted Root Filesystem
Placing a Disk Filesystem on a RAM Disk
Rootfs and Initramfs
Choosing a Filesystem's Type and Layout
Handling Software Upgrades
9. Setting Up the Bootloader
Embedded Bootloaders
Server Setup for Network Boot
Using the U-Boot Bootloader
10. Setting Up Networking Services
Network Settings
Busybox
Dynamic Configuration Through DHCP
The Internet Super-Server
Remote Administration with SNMP
Network Login Through Telnet
Secure Communication with SSH
Serving Web Content Through HTTP
Provisioning
11. Debugging Tools
Eclipse
Debugging Applications with gdb
Tracing
Performance Analysis
Memory Debugging
A Word on Hardware Tools
12. Introduction to Real-Time Linux
What Is Real-Time Processing?
Should Your Linux Be Real-Time?
Common Real-Time Kernel Requirements
Some Typical Users of Real-Time Computing Technology
The Linux Paths to Real-Time
13. The Xenomai Real-Time System
Porting Traditional RTOS Applications to Linux
The Xenomai Architecture
How Xenomai Works
The Real-Time Driver Model
Xenomai, Chameleon by Design
14. The RT Patch
Interrupts As Threads
Priority Inheritance
Configuring the Kernel with the RT Patch
High-Resolution Timers
The Latency Tracer
Conclusion
Index ...

.You need to be familiar with the development, programming, and debugging of embedded systems in general, from both the software and hardware perspectives.
Unix system administration
You need to be able to tend to various system administration tasks such as hardware configuration, system setup, maintenance, and using shell scripts to automate tasks.
Linux device drivers
You need to know how to develop and debug various kinds of Linux device drivers.
Linux kernel internals
You need to understand as much as possible how the kernel operates.
GNU software development tools
You need to be able to make efficient use of the GNU tools. This includes understanding many of the options and utilities often considered to be "arcane."
We assume that you are familiar with at least the basic concepts of each topic. On the other hand, you don't need to know how to create Linux device drivers to read this book, for example, or know everything about embedded system development. As you read through this book and progress in your use of Linux in embedded systems, you will likely feel the need to obtain more information regarding certain aspects of Linux's use.
Though this book discusses only the use of Linux in embedded systems, part of this discussion can certainly be useful to developers who intend to use one of the BSD variants in their embedded system. Many of the explanations included here will, however, need to be reinterpreted in light of the differences between BSD and Linux.
Organization of the Material
There are four major parts to this book. The first part is composed of Chapters 1 through 3. These chapters cover the preliminary background required for building any sort of embedded Linux system. Though they describe no hands-on procedures, they are essential to understand many aspects of building embedded Linux systems.
The second part spans Chapters 4 through 9. These important chapters lay out the essential steps involved in building any embedded Linux system. Regardless of your system's purpose or functionality, these chapters are required reading.
The third part of the book, which ended the first edition, is made up of Chapters 10 and 11 and covers material that, athough very important, is not essential to building embedded Linux systems.
The final partof the book, comprised of Chapters 12 through 14, is an in-depth discussion of real-time, including its different applications and when you should consider the various implementations and varieties available. We are lucky and honored to have chapters written by the implementors of the Xenomai cokernel and the RT patch to the Linux kernel.
Chapter 1, Introduction, gives an in-depth introduction to the world of embedded Linux. It lays out basic definitions and then introduces real-life issues about embedded Linux systems, including a discussion of open source and free software licenses from the embedded perspective. The chapter then introduces the example system used in other parts of this book and the implementation method used throughout the book.
Chapter 2, Basic Concepts, outlines the basic concepts that are common to building all embedded Linux systems.
Chapter 3, Hardware Support, provides a thorough review of the embedded hardware supported by Linux, and gives links to websites where the drivers and subsystems implementing this support can be found. This chapter discusses processor architectures, buses and interfaces, I/O, storage, general-purpose networking, industrial grade networking, and system monitoring.
Chapter 4, Development Tools, covers the installation and use of the various development tools used in building embedded Linux systems. This includes a discussion of Eclipse for embedded Linux development, and how to build and install the GNU toolchain components from scratch. It also includes sections discussing Java, Perl, Python, and other languages, along with a section about the various terminal emulators that can be used to interact with an embedded target.
Chapter 5, Kernel Considerations, discusses the selection, configuration, cross-compiling, installation, and use of the Linux kernel in an embedded system.
Chapter 6, Root Filesystem Content, updated for the second edition by Michael Opdenacker, explains how to build a root filesystem using the components introduced earlier in the book, including the installation of the C library and the creation of the appropriate/der entries. More importantly, this chapter covers the installation and use of BusyBox, embutils, and System V init.
Chapter 7, Storage Device Manipulation, updated for the second edition by kernel developer David Woodhouse, covers the intricacies of manipulating and setting up storage devices for embedded Linux systems. The chapter's emphasis is on solid-state storage devices, such as native flash and DiskOnChip devices, and the MTD subsystem.
Chapter 8, Root Filesystem Setup, explains how to set up the root filesystem created in Chapter 6 for the embedded system's storage device. This includes the creation of filesystem images (based on JFFS2, CRAMFS, or other specialized filesystems), and the use of disk-style filesystems over NFTL.
Chapter 9, Setting Up the Bootloader, discusses the various bootloaders available for use in each embedded Linux architecture. Special emphasis is put on the use of GRUB with DiskOnChip devices and U-Boot. Network booting using BOOTP/DHCP, TFTP, and NFS is also covered. ..
Chapter 10, Setting Up Networking Services, focuses on the configuration, installation, and use of software packages that offer networking services, such as SNMP, SSH, and HTTP.
Chapter 11, Debugging Tools, updated for the second edition by Michael Boerner, covers the main debugging issues encountered in developing software for embedded Linux systems. This includes the use of gdb in a cross-platform development environment, Eclipse, tracing, performance analysis, and memory debugging.
Chapter 12, Introduction to Real-Time Linux, explains the value of real-time and offers a candid discussion of when you need various real-time features, along with an introduction to the various ways you can achieve real-time behaviors using Linux. This chapter was written by the founder and maintainer of the Xenomai Real-Time System, Philippe Gerum.
Chapter 13, The Xenomai Real-Time System, also written by Philippe Gerum, offers a high-level view of how Xenomai achieves real-time goals and how it can be useful in conjunction with embedded Linux.
Chapter 14, The RT Patch, performs a similar function for the RT patch to the Linux kernel, explaining how to enable its features. The chapter was written by Steven Rostedt, a key developer on the patch.
Although Chapters 7 through 9 are independent, note that their content is highly interrelated. For example, setting up the target's storage device, as discussed in Chapter 7, requires a basic knowledge about the target filesystem organization as discussed in Chapter 8, and vice versa. So, too, does setting up storage devices require a basic knowledge of bootloader setup and operation as discussed in Chapter 9, and vice versa. We therefore recommend that you read Chapters 7 through 9 in one breath a first time before carrying out the instructions in any of them. When setting up your target thereafter, you will nevertheless follow the same sequence of operations outlined in these chapters.
Hardware Used in This Book
As you'll see in Chapter 3, Linux supports a very wide range of hardware. For this book, we've used a number of embedded systems to test the various procedures. Some of these systems, such as the OpenMoko-based NEO 1973, are commercial products available in the mainstream market. We included these intentionally, to demonstrate that any willing reader can find the materials to support learning how to build embedded Linux systems. You can, of course, still use an old x86 PC for experimenting, but you are likely to miss much of the fun, given the resemblance between such systems and most development hosts.
To illustrate the range of target architectures on which Linux can be used, we varied the target hardware we used in the examples between chapters. Though some chapters are based on different architectures, the commands given in each chapter apply readily to other architectures as well. if, for instance, an example in a chapter relies on the arm-linux-gcc command, which is the gcc compiler for ARM, the same example would work for a PPC target by using the powerpc-linux-gcc command instead. Whenever more than one architecture is listed for a chapter, the main architecture discussed is the first one listed. The example commands in Chapter 5, for instance, are mainly centered around PowerPC, but there are also a few references to ARM commands.
Unless specific instructions are given to the contrary, the host's architecture is always different from the target's. In Chapter 4, for example, we used a PPC host to build tools for an x86 target. The same instructions could, nevertheless, be carried out on a SPARC or an S/390 with little or no modification. Note that most of the content of the early chapters is architecture- independent, so there is no need to provide any architecturespecific commands.
Software Versions
The central software on which an embedded Linux system depends, of course, is the Linux kernel. This book concentrates on version 2.6 of the Linux kernel, and 2.6.22 in particular. Changes to the kernel will probably have only a benign effect on the information in the book. That is, new releases will probably support more hardware than Chapter 3 lists. But the essential tasks described in this book are unlikely to change.
In addition, this book discusses the configuration, installation, and use of over 40 different open source and free software packages. Each package is maintained independently and is developed at a different pace. Because these packages change over time, it is likely that the package versions covered in this book may be outdated by the time you read it. In an effort to minimize the effect of software updates on the text, we have kept the text as version-independent as possible. The overall structure of the book and the internal structure of each chapter, for example, are unlikely to vary regardless of the various software changes. Also, many packages covered in this book have been around for quite some time, so they are unlikely to change in any substantial way. For instance, the commands to install, set up, and use the different components of the GNU development toolchain, which is used throughout this book, have been relatively constant for a number of years and are unlikely to change in any substantial way in the future. This statement applies equally to most other software packages discussed.
Acknowledgments for the First Edition
E quindi uscimmo a riveder le stelle.* It is with these words that Dante ends Inferno, the first part of his Divine Comedy. Though it would be misleading to suggest that writing this book wasn't enjoyable, Dante's narrative clearly expresses the feeling of finishing a first iteration of the book you now hold in your hands. In particular, I have to admit that it has been a challenging task to pick up the bits and pieces of information available on the use of Linux in embedded systems, to complete this information in as much as possible, and put everything back together in a single, straightforward manuscript that provides a practical method for building embedded Linux systems. Fortunately, I was aided in this task by very competent and willing people.
First and foremost, I would like to thank Andy Oram, my editor. Much like Virgil assisted Dante in his venture, Andy shepherded me throughout the various stages of writing this book. Among many other things, he patiently corrected my nonidiomatic phrases, made sure that my text actually conveyed the meaning I meant for it to convey, and relentlessly pointed out the sections where I wasn't providing enough detail. The text you are about to read is all the much better, as it has profited from Andy's input. By the same token, I would like to thank Ellen Siever, with whom I initially started working on this book. Though our collaboration ended earlier than I wished it had, many of the ideas that have made their way into this final version of the book have profited from her constructive feedback.
I have been extremely fortunate to have an outstanding team of reviewers go over this book, and am very grateful for the many hours they poured into reading, correcting, and pointing out problems with various aspects of this book. The review team was made up of Erik Andersen, Wolfgang Denk, Bill Gatliff, Russell King, Paul Kinzelman, Alessandro Rubini, David Schleef, and David Woodhouse. I'd like to especially thank Alessandro for his dogged pursuit of perfection. Any remaining errors you may find in the following pages are without a doubt all mine.
Writing about the use of Linux in embedded systems requires having access to a slew of different hardware. Given that embedded hardware is often expensive, I would like to thank all the companies and individuals who have stepped forward to provide me with the appropriate equipment. In particular, I would like to thank Stephane Martin of Kontron for providing a Teknor VIPer 806 board, Wolfgang Denk of DENX Software Engineering for providing a TQ components TQM860L PPC board, and Steve Papacharalambous and Stuart Hughes of Zee2 for providing a uCdimm system.
I have found much of the incentive and thrust for writing this book from being a very satisfied open source and free software user and contributor who has profited time and again from the knowledge and the work produced by other members of this community. For this, I have many people to thank. Primarily, I'd like to thank Michel Dagenais for his trust, his guidance, and for giving me the chance to freely explore uncharted terrain. My work on developing the Linux Trace Toolkit, as part of my masters degree with Michel, got me more and more involved in the open source and free software community. As part of this involvement, I have met a lot of remarkable individuals whose insight and help I greatly appreciate. Lots of thanks to Jacques Gelinas, Richard Stallman, Jim Norton, Steve Papacharalambous, Stuart Hughes, Paolo Mantegazza, Pierre Cloutier, David Schleef, Wolfgang Denk, Philippe Gerum, Loic Dachary, Daniel Phillips, and Alessandro Rubini.
Last, but certainly not least, I owe a debt of gratitude to Sonia for her exceptional patience as I spent countless hours testing, writing, testing some more, and writing even more. Her support and care have made this endeavor all the more easy to carry out. La main invisible qui a ecrit les espaces entre les lignes est la sienne et je lui en suis profondement reconnaissant.
Acknowledgments for the Second Edition
When Karim first mentioned updating Building Embedded Linux Systems, I could not have imagined what a fun and wild ride it would be. I was in the final stages of moving from the U.K. to the U.S. at the time, and life was pretty hectic for quite a while. Along the way, some great friends and coauthors have helped to turn an idea into the reality of the book that you are now reading. And we collectively hope that we have served to increase the range of documentation available on embedded Linux.
First and foremost, I would like to thank my friend Karim Yaghmour for letting me run amock with his original manuscript, Andy Oram for his patient advice and editorial wizardry, and Isabel Kunkle for assisting Andy in putting up with a bunch of authors with busy schedules. I would also like to thank Marlowe Shaeffer and the team at O'Reilly for their steadfast attention to detail, especially near the end of the project.
I would like to thank my coauthors for stepping up to the plate and helping to see this project through: Michael Boerner, Michael Opdenacker, Steven Rostedt, Gilad Ben-Yossef (CTO, Codefidence Ltd.), Phillipe Gerum, and David Woodhouse. I've known most of you for many years, even if We only get to meet once a year at the Linux Symposium, and I am grateful that you have helped to improve the overall quality of this book. In a similar vain, I am grateful to the review comments from Tim Rikers, Vince Skahan, and Mark VandenBrink, as well as the many others I have occasionally spoken with about this book. But all that said, any remaining mistakes and technical omissions are entirely my responsibility, though we hope there are few.
Embedded Linux would mean nothing without the hard work of many thousands of people all over the world. Some of those people have gotten involved in the first or second editions of this book, while there are many, many more people out there helping to make Linux the most valuable and viable choice for embedded developers. It would be tricky to even attempt to list these people by name, and so I would like to instead offer my most sincere thanks to everyone concerned--I'd also like to encourage readers to thank those who provide the upstream for their development projects. Please do also encourage your employers and customers to do the same through whatever means you feel is most appropriate.
I would like to thank my friends and family for their never-ending support of my many pursuits and random craziness. My mum and dad rarely see me these days (I live 3,000 miles away in another country, on an awkward time delay) but have always been the best parents you could wish for, in spite of their son turning out to be a "traitor's dog" (thanks, dad, for your whimsical historical insight right there!) who joined the Americans. My sister Hannah and brother-in-law Joe Wrigley (another Red Hatter!) have always been amazing, as has my youngest sister Holly. My grandmother keeps me informed of family goings on with her letters, which I always look forward to reading far away from a computer.
Many friends contributed to the overall success of this project without even realizing it. They include Deepak Saxena, Hussein Jodiyawalla, Bill Weinberg, Alison Cornish, Grace Mackell, Andrew Schliep, Ginger Diercks, Kristin Mattera and James Saunders, Karen Hopkins, Andrew Hutton, and Emilie Moreau (and also Denali and Nihao), Madeleine and Chris Ball, Tim Burke, Lon Hohberger, Chris Lumens, Jon Crowe, Rachel Cox, Catherine Nolan, TobyJaffey (and Sara and Milly), David Brailsford, Jeff and Nicole Stern, Catherine Davis, Mary-Kay and Luke Jensen, Philippe De Swert, Matt Domsch, Grant Likely (of Secret Lab), Hetal Patel, Mark Lord, Chris Saul, Dan Scrase, and David Zeuthen. A special thanks to Sven-Thorsten Dietrich and Aaron Nielson for their like-minded craziness at just the right moments.
Finally, I am very grateful to my good friend David Brailsford of the University of Nottingham, and to Malcolm Buckingham and Jamie McKendry of Oxford Instruments for believing in me and letting me experiment with Linux and superconducting magnets, and to lan Graham of MontaVista UK Ltd. for the opportunity to work on some great projects during my time there. I also owe Andrew Hutton and Craig Ross of Steamballoon (and organizers of Linux Symposium) thanks for their support of my embedded endeavors over the years. I would especially like to thank Gary Lamb (Global Engineering Services--our embedded team), Clark Williams, and Tim Burke of Red Hat, Inc. for their continued support, as well as all of my friends at Red Hat and at other great Linux companies. ...
--Jon Masters, Cambridge, Massachusetts