eCos嵌入式软件开发实战指南

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"《Embedded software development with eCos》是由Anthony J. Massa撰写的一本关于eCos嵌入式软件开发的专业书籍，属于Bruce Perens' Open Source系列。书中详细介绍了如何进行eCos开发，尽管出版时间较早，但对于理解和实践eCos系统仍然具有指导价值。" 在这本书中，作者Anthony J. Massa深入探讨了嵌入式计算机系统的设计和编程，特别是关注使用eCos（嵌入式实时操作系统）这一开源平台进行应用软件的开发。eCos，全称Embedded Configurable Operating System，是一个高度可配置的实时操作系统，适用于各种嵌入式设备，包括微控制器和系统级芯片（SoC）。书中内容可能涵盖了以下几个关键知识点： 1. **eCos介绍**：详细阐述eCos的基本架构、设计原则和特点，包括其模块化设计、可配置性以及对实时性需求的支持。 2. **嵌入式系统基础**：讲解嵌入式系统的概念，包括硬件与软件的关系、嵌入式处理器的特性、内存管理以及嵌入式软件开发的基本流程。 3. **eCos配置与构建**：介绍如何根据项目需求配置eCos内核和中间件，以及如何构建和编译整个系统。 4. **实时数据处理**：讨论实时操作系统中的数据处理策略，包括任务调度、中断处理和同步机制。 5. **应用程序开发**：详细解释如何在eCos上开发和调试应用程序，包括使用eCos提供的API和工具链。 6. **硬件接口编程**：讲解如何与硬件进行通信，如驱动程序的编写和设备控制。 7. **调试与测试**：介绍eCos环境下的调试工具和测试策略，以确保软件质量和性能。 8. **案例研究**：通过实际的项目例子来展示eCos在不同应用场景中的应用，提供实践指导。 9. **维护与更新**：讨论如何在产品生命周期中管理和更新eCos系统，包括固件升级和错误修复。这本书对于从事嵌入式开发的工程师来说是一份宝贵的资源，它不仅提供了理论知识，还提供了实践经验，帮助读者更好地理解和掌握eCos在嵌入式软件开发中的应用。尽管出版时间较早，但eCos的核心原理和技术依然适用于当前的嵌入式系统开发，因此，该书仍具有很高的参考价值。

xviii Preface

Since eCos is open source, you, the developer, are in complete control over your embed-

ded software destiny. Even the tools described in the eCos development system are open source,

thereby allowing you to become completely self sufﬁcient—although the eCos development

community is out there available to lend help when needed.

Book Layout and Overview

Let’s take a look at the layout of the book and get an overview of what is covered and where it is

located. This enables you to focus on the speciﬁc aspects of eCos that you need to understand.

The layout of the book is intended to build on information covered in earlier chapters. We

start with understanding the key components within eCos, then move to additional functionality

offered in the system, and ﬁnally, get down to using eCos and the development environment.

For developers new to the eCos world, or embedded software altogether, it is helpful to

understand the components that make up the eCos system by starting at the beginning. This

gives the baseline understanding of the different features provided by eCos. You can then imple-

ment these software components in an actual system.

More experienced developers looking for an evaluation of eCos can skip to the later chap-

ters and begin experimenting right away. The format of the development platform installation

and examples allow a quick setup of the tools and immediate results. This lets you answer the

question, “will eCos work for me?”

Current eCos users can ﬁll in any holes that might be present in their eCos knowledge, by

looking at some of the eCos concepts from a different point of view.

Chapter 1,

An Introduction to the eCos World

, begins with a brief introduction to eCos,

which includes a background about the eCos open-source project and the company behind its

start. A description of the eCos terminology is detailed as well. This terminology is used

throughout the book and in the eCos development community. The beginning of the book is

intended to provide developers who are unfamiliar with eCos a means to become acquainted

with the eCos open-source project.

Next, we discuss the key components within the eCos system, presenting a closer look

under the hood of these major software modules. The key component chapters offer an under-

standing about how the different software modules work independently and together to provide

functionality required by the system.

Chapter 2,

The Hardware Abstraction Layer

, focuses on the software closest to the hard-

ware that enables higher-level software modules to be unaware of the low-level functioning of

the hardware.

In Chapter 3,

Exceptions and Interrupts

, we detail exceptions and interrupts and show how

they are set up and handled in the eCos system. We discuss virtual vectors in Chapter 4,

Virtual

Vectors

, which provide a means to share services between ROM and RAM applications.

The heart of the eCos RTOS, the kernel, is the focus in Chapter 5, The Kernel. The kernel

supplies the scheduling functionality and the synchronization mechanisms for the software.

Moving on to Chapter 6, Threads and Synchronization Mechanisms, we discuss the basic unit of

Preface xix

execution in eCos, the thread, and provide a detailed look at the various synchronization mecha-

nisms supported by eCos.

Chapter 7, Other eCos Architecture Components, continues with our look at the different

eCos components by focusing on timing components, asserts and tracing functionality, and the I/O

control system.

Chapter 8, Additional Functionality and Third-Party Contributions, includes a broader

look at some of the additional features available for eCos developed by the eCos project main-

tainers and third-party contributors. These include networking support, ROM monitors, ﬁle sys-

tems, PCI support, USB support, and the GoAhead WebServer.

In Chapter 9, The RedBoot ROM Monitor, we focus on the RedBoot ROM monitor. This

standalone program is designed for embedded systems to provide a debugging and bootstrap

environment. RedBoot is an eCos-based application and uses the eCos Hardware Abstraction

Layer (HAL) for its foundation.

We begin our hands-on experience in Chapter 10, The Host Development Platform, with

the installation of the host development tools. We discuss the Cygwin native tools, the GNU

cross-development tools, and the eCos development kit. We also cover the installation of a Con-

current Versions System (CVS) client, WinCVS, to enable access to the online eCos source code

repository. This gives you the ability to take advantage of any bug ﬁxes or extended functionality

contributed to the eCos source code.

In Chapter 11, The eCos Toolset, we delve into the eCos toolset with a detailed look at

how the tools operate on the eCos source code, and the layout of the tools. Also included are

some other open-source tools to round out and complete our open-source embedded develop-

ment system. This prepares us for the next step, putting the tools to work to build our applica-

tion.

Chapter 12, An Example Application Using eCos, lets you put your knowledge to work.

The chapter starts with an overview of the eCos build process, followed by a build of the Red-

Boot ROM monitor. We then do a build of the eCos real-time operating system, and, ﬁnally, put

it all together by building an application. This chapter provides a baseline on which you can then

add additional components to assemble a system to meet your embedded software requirements.

Finally, Chapter 13, Porting eCos, closes with a look at porting eCos onto another hard-

ware platform. This is key to getting your application running on your new target hardware plat-

form, which is typically the main goal in embedded software development.

Development System and Examples

As mentioned previously, in Chapter 10 we go through the process of setting up an eCos devel-

opment system. This development system includes the native Cygwin tools for Windows, the

GNU cross-development tools (binutils, compiler, and debugger), the eCos conﬁguration and

management tools, a CVS client, and a lint program.

This system enables you to conﬁgure and build the eCos library, which is then linked with

an application to run the eCos RTOS. The RedBoot ROM monitor is also built using this system.

xx Preface

After following the steps in Chapter 10, a complete open-source embedded software develop-

ment environment is conﬁgured.

We go through examples of building RedBoot, the eCos library, and an application in

Chapter 12. Rather than requiring a speciﬁc development board to run the examples, a second

PC is needed for the target platform. This is a better approach to becoming familiar with the

development tools since it’s typically pretty easy to ﬁnd a spare PC lying around.

Although GNU cross-development tools binary ﬁles are included on the CD-ROM for the

Intel x86 and PowerPC processor architectures, the instructions for conﬁguring and building the

GNU cross-development tools for other processor architectures are provided in Appendix D,

Building the GNU Cross-Development Tools.

The embedded software development tools are installed, and examples are built, on a Win-

dows development system. However, the necessary ﬁles to get an embedded software develop-

ment system up and running on a Linux system are included on the CD-ROM. Since the eCos

conﬁguration tools are able to run on both Linux and Windows, the procedure for building and

running the examples applies to both host operating systems.

The CD-ROM accompanying this book contains the ﬁles needed to set up the complete

embedded software development system for eCos as detailed in Chapter 10. The examples in

Chapters 12 and 13 are also contained on the CD-ROM under the examples directory.

A web site is available to download the source code and updates. The site is located online at:

www.phptr.com/massa/

If you ﬁnd any errors that need correction, feel free to contact me and I will update the

source code accordingly.

Some Notes about the Book

All example code in this book is in C or assembly language. eCos also uses the Component Def-

inition Language (CDL), an extension of the existing Tool Command Language (Tcl) scripting

language. We cover this in Chapter 11.

In the text where a 32-bit hexadecimal value is shown, the most signiﬁcant 16 bits and least

signiﬁcant 16 bits are separated by an underscore (“_”) (e.g., 0xABCD_EF12) for readability.

Sidebars are also included, which are used to point out important or additional informa-

tion. The sidebars look like the following:

This book includes several Uniform Resource Locator (URL) links showing where addi-

tional information can be obtained on the Internet. The most up-to-date links are included in the

text; however, we all know that links can have a ﬁnite existence.

Item lists throughout the book detail the eCos kernel API functions. These lists contain a

ﬁeld named “Context.” This ﬁeld shows the context from where the speciﬁed function can be

N O T E Example of a sidebar.

Preface xxi

called. The different contexts are Initialization, Thread, ISR, and DSR. “Any” is used to desig-

nate that the function can be called from any of the contexts.

A Brief Take on Open Source Development

There have always been “agnostics” in the debate of open source versus closed source—it some-

times comes down to whether the funding is available to purchase software tools and support.

Each has its beneﬁts and shortcomings, so let’s take a brief look at some of the pros and cons

developers have found when working on both sides of the open-source and closed-source fence.

What it ultimately comes down to is, does the product work, and can the schedule and cost bud-

get be met using this solution?

Open source can be a confusing term. In an article written by Daniel Benenstein,

states that open source is free software in the sense of freedom of knowledge exchange. Much

more reliance is placed on the individual developer to ﬁnd problems, correct the problems, and

make the solution available to others in the open-source community. This iterative process is the

method that creates a more robust and bug-free code base.

Presumably, because the draw of talent is worldwide, the best and brightest developers are

working to make the product better. With closed source, a development support team is assem-

bled to work on ﬁxing problems for code they probably did not create. The team assembled

might be very talented; however, the pool of talent from which to draw is very small compared

to a worldwide talent pool.

Often times, closed-source, or proprietary, software and open-source software work hand in

hand to complement each other. Many proprietary products are derived from open-source projects.

Proprietary software must be innovative and differentiate itself from the open-source alternative;

otherwise, why would people pay for something that they can get for free? Looking at things from

this point of view, open source pushes proprietary software to the extreme of innovation.

There are some general advantages and disadvantages to using open-source software.

One advantage is that since the source is available if you are not able to get support from the

open-source community, you can dive right in and ﬁnd out exactly what is going on with the code.

There is no need to wait for support from an external source, which can reduce debug time

drastically.

Another advantage of open-source software is that it is not tied to any one speciﬁc company.

In the case of proprietary software, if the owning company changes direction, or disappears, then

the application developers using that solution are left out in the cold. Open-source software pre-

vents this because developers have full access to the code and can choose the path for their own

system software.

Sometimes vendors selling proprietary software are not always the most responsive to all

customers using their product. In cases where a project is not destined to produce large volumes,

the vendor’s response to questions might not be as rapid as needed. The reality is that a company

with higher revenue products will get the preferential treatment.

Benenstein, Daniel. “Galleo Linux Multimedia Communicator.” Embedded Linux Journal (July/August 2001): 14–19.

xxii Preface

Having the source also gives you the ability to implement your own changes and custom-

ize the code exactly the way you need to for your speciﬁc application. In addition, only with

open-source can the source-level conﬁguration method, as we ﬁnd in eCos, be used.

Although some proprietary software vendors offer their source code to developers, there is

often a fee associated with getting said code.

Security is often looked at as a negative aspect of open-source developments. Because all

of the source code is available to everyone, malicious developers can exploit security holes. On

the other hand, the community of developers supporting the open-source project work quickly

on a ﬁx because it is in their best interest as well. You are not at the mercy of a single source pro-

viding a ﬁx to the security problem.

A great source for getting viewpoints from some of the leading ﬁgures behind the open-

source movement is Open Sources: Voices from the Open Source Revolution.

Acknowledgments

This book could not have been completed without the hard work and tremendous effort of other

people. I would like to start by thanking the technical reviewers, Jonathan Larmour (a.k.a. Jifl)—

I appreciate your very insightful comments—and the technical support (occasionally real-time)

throughout the development of this book. Other reviewers I am indebted to for sharing their keen

comments and extremely valuable views include Grant Edwards, Bart Veer, Bill Gatliff, Larry

Mittag, and Paul Beskeen. I would like to thank Michael Tiemann for writing the Foreword for

this book.

I would like to thank the editor, Mark Taub—I appreciate the feedback and support you

gave throughout this process.

Many thanks to the companies and open-source projects whose software is included on

this CD-ROM—some brilliant stuff there.

Closing on a Personal Note

I would like to thank my Nonno and Nonna for all their support throughout my life. They are

always there for me providing whatever is needed whether it’s encouragement, a getaway to the

backcountry for a ride and lunch, or a trip to the Boll Weevil. I sure miss Nonna. I love you both

very much.

I would like to thank my brother, Laurie, and sister, Catherine, for their encouragement

and understanding. You two are the best brother and sister anyone can ask for. By the way, I’d

also like to congratulate my sister on passing the CPA exam, although I do believe the score is

now 2 to 1—in my favor. :) I love you guys.

Thank you Mom and Dad for your never-ending support and encouragement for things I

attempt in my career, and especially for things I attempt throughout my life. You are always

there for me in whatever I do. I am very thankful to have such wonderful parents. I love you with

all my heart.

DiBona, Chris; Ockman, Sam; Stone, Mark. Open Sources: Voices from the Open Source Revolution (O’Reilly, 1999).

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