Real Time Computing

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Real-Time Computing

Professor John A. Stankovic Department of Computer Science University of Massachusetts Amherst, MA 01003 April 16, 1992

1 What is a Real-Time System

Real{time systems are de ned as those systems in which the correctness of the system depends not only on the logical result of computation, but also on the time at which the results are produced. Real-time systems span a broad spectrum of complexity from very simple microcontrollers (such as a microprocessor controlling an automobile engine) to highly sophisticated, complex and distributed systems (such as air tra c control for the continental United States). Other examples of real-time systems include command and control systems, process control systems, ight control systems, the space shuttle avionics system, exible manufacturing applications, the space station, space-based defense systems, intensive care monitoring, collections of humans/robots coordinating to achieve common objectives (usually in hazardous environments such as undersea exploration or chemical plants), intelligent highway systems, and multimedia and high speed communication systems. We are also beginning to see many of these real-time systems adding expert systems 22] and other AI technology creating additional requirements and complexities. Real-time systems technology is a key enabling technology for the future in an ever-growing domain of important applications. Because of this fact, it is important to understand the current technology and its limitations and to devote signi cant e ort for improving the technology. Typically, a real{time system consists of a controlling system and a controlled system. For example, in an automated factory (Figure 1), the controlled system is the factory oor with its robots, assembling stations, and the assembled parts, while the controlling system is the computer and human interfaces that manage and coordinate the activities on the factory oor. Thus, the controlled system can be viewed as...