ch15 - Real-time Software Design Ian Sommerville 2004...

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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 1 Real-time Software Design
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 2 Objectives To explain the concept of a real-time system and why these systems are usually implemented as concurrent processes To describe a design process for real-time systems To explain the role of a real-time operating system To introduce generic process architectures for monitoring and control and data acquisition systems
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 3 Topics covered System design Real-time operating systems Monitoring and control systems Data acquisition systems
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 4 Real-time systems Systems which monitor and control their environment. Inevitably associated with hardware devices Sensors : Collect data from the system environment; Actuators : Change (in some way) the system's environment; Time is critical. Real-time systems MUST respond within specified times.
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 5 Definition A real-time system is a software system where the correct functioning of the system depends on the results produced by the system and the time at which these results are produced. A soft real-time system is a system whose operation is degraded if results are not produced according to the specified timing requirements. A hard real-time system is a system whose operation is incorrect if results are not produced according to the timing specification.
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 6 Stimulus/Response Systems Given a stimulus, the system must produce a response within a specified time. Periodic stimuli . Stimuli which occur at predictable time intervals For example, a temperature sensor may be polled 10 times per second. Aperiodic stimuli . Stimuli which occur at unpredictable times For example, a system power failure may trigger an interrupt which must be processed by the system.
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 7 Architectural considerations Because of the need to respond to timing demands made by different stimuli/responses, the system architecture must allow for fast switching between stimulus handlers. Timing demands of different stimuli are different so a simple sequential loop is not usually adequate. Real-time systems are therefore usually designed as cooperating processes with a real-time executive controlling these processes.
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 8 A real-time system model
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 9 Sensor/actuator processes
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©Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 15 Slide 10 System elements Sensor control processes
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This note was uploaded on 10/01/2010 for the course CS 1292 taught by Professor Aabdollah during the Spring '10 term at NJ City.

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ch15 - Real-time Software Design Ian Sommerville 2004...

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