Preface

Xiaocong Fan, Erie, PA

An embedded system is an electronic system that is designed to perform a dedicated function within a larger system. Real-time systems are those that can provide guaranteed worst-case response times to critical events, as well as acceptable average-case response times to noncritical events. When a real-time system is designed as an embedded component, it is called a real-time embedded system. Real-time embedded systems are widespread in consumer, industrial, medical, and military applications.

As more and more of our daily life depends on embedded technologies, the demand for engineers with the skill set for the development of real-time embedded software has soared in recent years. As a consequence, preparing students for the design and implementation of embedded software is becoming increasingly important. This textbook is written especially for advanced undergraduates or master-level students who are pursuing a major in software engineering, computer engineering, or a related discipline. The textbook may also benefit practicing engineers with a concentration in embedded software development.

This book takes a synergetic approach to introducing ideas and topics from real-time systems, embedded systems, and software development principles. Readers will not only gain a thorough understanding of concepts related to microprocessors, interrupts, and the cross-platform development process, and appreciate the importance of real-time modeling and scheduling, they will also be trained in good software engineering practices such as model documentation, model analysis, design patterns, and system standard conformance.

This textbook features three aspects that are essential for the development of real-time embedded software.

First, developing software for real-time embedded systems involves many activities, including specification of requirements, timing analysis, architecture design, multitasking design, and cross-platform testing and debugging. This book covers the whole process of embedded software development, with some topics fully explained and others only briefly mentioned (e.g., debugging and testing). In particular, this book presents various embedded software architectures in a systematic way, with a focus on a real-time operating system, which is the most advanced architecture adopted in large real-time embedded systems. Moreover, we have chosen to place significant emphasis on reusable design solutions. As shown in Table 0.1, this book introduces many design patterns, which represent the best practices that can be reused in a wide range of real-time embedded systems.

Table 0.1

Summary of design patterns

DAS, detect-acknowledge-service; FIFO, first in first out; ISR, interrupt service routine.

Second, Unified Modeling Language (UML) is a graphical language for specifying, visualizing, constructing, and documenting software systems. UML is useful in a variety of engineering problems, from single-process, embedded systems and stand-alone user applications to concurrent, distributed systems. This text features UML 2.4, the latest UML standard as of this writing. Throughout the book, UML diagrams are used for both system designs and concept illustrations. In particular, the UML real-time profile is carefully presented so that students can learn how to document their designs of real-time systems in a professional way.

Third, POSIX (for "portable operating system interface") is an open operating system interface standard that has been developed to promote interoperability and portability of applications across variants of Unix operating systems. Software systems built upon one real-time operating system can be easily ported to other POSIX-compliant operating systems. This text features POSIX.1-2008 (2013 edition). The operating system services and concepts covered in this book are fully compatible with the POSIX.1-2008 standard. The example codes provided in this book have been tested in QNX-a real-time operating system widely adopted in industry. Since QNX is POSIX compliant, the programs may also be compiled, without changing the source code, for execution on another POSIX-compliant operating system.

Briefly, this textbook consists of four parts:

 Part I is dedicated to a basic introduction to real-time embedded systems and the iterative development process. Although our emphasis is on the software aspects, complete isolation from the underlying hardware is neither feasible nor desirable. For such a reason, this part also contains two chapters on microprocessors and interrupts-fundamental topics for software engineers who wish to build embedded systems.

 Part II is dedicated to modeling techniques for real-time systems. In particular, we introduce the modeling tools covered by UML-a standard widely adopted in both academia and the software industry. Moreover, we introduce real-time UML-a profile for specifying real-time-related constraints in system models. UML diagrams are consistently used throughout the book to illustrate key concepts and design patterns.

 Part III is dedicated to the design of software architectures for real-time embedded systems. We start with generic architectures, which lead us to the most complicated architecture-a real-time operating system. The focus is then switched to multitasking and real-time scheduling-two critical issues to be addressed by any designers of real-time embedded systems.

 Part IV is dedicated to system implementation. We especially focus on those mechanisms available on any POSIX-compliant operating systems; this means that the design/implementation patterns given in this book are applicable to other POSIX-compliant operating systems as well.

The four parts together have 23 chapters. A one-semester course can use selected chapters/sections to suit the interests of the instructor and students. For instance, some microprocessor types in Chapter 3 can be skipped in order to fit the materials in one or two lecture time. If UML basic modeling concepts have been covered in a prerequisite...