Real-Time Systems Design and Analysis

Tools for the Practitioner

Phillip A. Laplante, Seppo J. Ovaska

• Éditeur: Wiley-IEEE Press
• Année: 2011
• ISBN:
  9781118136591
• Édition: 4
• Sujet: Physical Sciences
• Sous-sujet: Waves & Wave Mechanics

The leading text in the field explains step by step how to write software that responds in real time

From power plants to medicine to avionics, the world increasingly depends on computer systems that can compute and respond to various excitations in real time. The Fourth Edition of Real-Time Systems Design and Analysis gives software designers the knowledge and the tools needed to create real-time software using a holistic, systems-based approach. The text covers computer architecture and organization, operating systems, software engineering, programming languages, and compiler theory, all from the perspective of real-time systems design.

The Fourth Edition of this renowned text brings it thoroughly up to date with the latest technological advances and applications. This fully updated edition includes coverage of the following concepts:

• Multidisciplinary design challenges
  
  

• Time-triggered architectures
  
  

• Architectural advancements
  
  

• Automatic code generation
  
  

• Peripheral interfacing
  
  

• Life-cycle processes
  
  

The final chapter of the text offers an expert perspective on the future of real-time systems and their applications.

The text is self-contained, enabling instructors and readers to focus on the material that is most important to their needs and interests. Suggestions for additional readings guide readers to more in-depth discussions on each individual topic. In addition, each chapter features exercises ranging from simple to challenging to help readers progressively build and fine-tune their ability to design their own real-time software programs.

Now fully up to date with the latest technological advances and applications in the field, Real-Time Systems Design and Analysis remains the top choice for students and software engineers who want to design better and faster real-time systems at minimum cost.

1
FUNDAMENTALS OF REAL-TIME SYSTEMS

The term “real time” is used widely in many contexts, both technical and conventional. Most people would probably understand “in real time” to mean “at once” or “instantaneously.” The Random House Dictionary of the English Language (2nd unabridged edition, 1987), however, defines “realtime” as pertaining to applications in which the computer must respond as rapidly as required by the user or necessitated by the process being controlled. These definitions, and others that are available, are quite different, and their differences are often the cause of misunderstanding between computer, software and systems engineers, and the users of real-time systems. On a more pedantic level, there is the issue of the appropriate writing of the term “real-time.” Across technical and pedestrian literature, various forms of the term, such as real time, real-time, and realtime may appear. But to computer, software, and systems engineers the preferred form is real-time, and this is the convention that we will follow throughout this text.

Consider a computer system in which data need to be processed at a regular rate. For example, an aircraft uses a sequence of accelerometer pulses to determine its position. Systems other than avionic ones may also require a rapid response to events that occur at nonregular rates, such as handling an overtemperature failure in a nuclear power plant. Even without defining the term “real-time,” it is probably understood that those events demand timely or “real-time” processing.

Now consider a situation in which a passenger approaches an airline check-in counter to pick up his boarding pass for a certain flight from New York to Boston, which is leaving in five minutes. The reservation clerk enters appropriate information into the computer, and a few seconds later a boarding pass is printed. Is this a real-time system?

Indeed, all three systems—aircraft, nuclear power plant, and airline reservations—are real-time, because they must process information within a specified interval or risk system failure. Although these examples may provide an intuitive definition of a real-time system, it is necessary to clearly comprehend when a system is real-time and when it is not.

To form a solid basis for the coming chapters, we first define a number of central terms and correct common misunderstandings in Section 1.1. These definitions are targeted for practitioners, and thus they have a strong practical point-of-view. Section 1.2 presents the multidisciplinary design challenges related to real-time systems. It is shown that although real-time systems design and analysis are subdisciplines of computer systems engineering, they have essential connections to various other fields, such as computer science and electrical engineering—even to applied statistics. It is rather straightforward to present different approaches, methods, techniques, or tools for readers, but much more difficult to convey the authors’ insight on real-time systems to the audience. Nevertheless, our intention is to provide some insight in parallel with specific tools for the practitioner. Such insight is built on practical experiences and adequate understanding of the key milestones in the field. The birth of real-time systems, in general, as well as a selective evolution path related to relevant technological innovations, is discussed in Section 1.3. Section 1.4 summarizes the preceding sections on fundamentals of real-time systems. Finally, Section 1.5 provides exercises that help the reader to gain basic understanding on real-time systems and associated concepts.

1.1 CONCEPTS AND MISCONCEPTIONS

The fundamental definitions of real-time systems engineering can vary depending on the resource consulted. Our pragmatic definitions have been collected and refined to the smallest common subset of agreement to form the vocabulary of this particular text. These definitions are presented in a form that is intended to be most useful to the practicing engineer, as opposed to the academic theorist.

1.1.1 Definitions for Real-Time Systems

The hardware of a computer solves problems by repeated execution of machine-language instructions, collectively known as software. Software, on the other hand, is traditionally divided into system programs and application programs.

System programs consist of software that interfaces with the underlying computer hardware, such as device drivers, interrupt handlers, task schedulers, and various programs that act as tools for the development or analysis of application programs. These software tools include compilers, which translate high-level language programs into assembly code; assemblers, which convert the assembly code into a special binary format called object or machine code; and linkers/locators, which prepare the object code for execution in a specific hardware environment. An operating system is a specialized collection of system programs that manage the physical resources of the computer. As such, a real-time operating system is a truly important system program (Anh and Tan, 2009).

Application programs are programs written to solve specific problems, such as optimal hall-call allocation of an elevator bank in a high-rise building, inertial navigation of an aircraft, and payroll preparation for some industrial company. Certain design considerations play a role in the design of system programs and application software intended to run in real-time environments.

The notion of a “system” is central to software engineering, and indeed to all engineering, and warrants formalization.

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Definition: System

A system is a mapping of a set of inputs into a set of outputs.

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When the internal details of the system are not of particular interest, the mapping function between input and output spaces can be considered as a black box with one or more inputs entering and one or more outputs exiting the system (see Fig. 1.1). Moreover, Vernon lists five general properties that belong to ...