ch13 - ©Ian Sommerville 2000 Software Engineering, 6th...

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Unformatted text preview: ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 1 Real-time Software Design l Designing embedded software systems whose behaviour is subject to timing constraints ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 2 Objectives l To explain the concept of a real-time system and why these systems are usually implemented as concurrent processes l To describe a design process for real-time systems l To explain the role of a real-time executive l To introduce generic architectures for monitoring and control and data acquisition systems ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 3 Topics covered l Systems design l Real-time executives l Monitoring and control systems l Data acquisition systems ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 4 Real-time systems l Systems which monitor and control their environment l Inevitably associated with hardware devices • Sensors: Collect data from the system environment • Actuators: Change (in some way) the system's environment l Time is critical. Real-time systems MUST respond within specified times ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 5 Definition l 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 l A ‘soft’ real-time system is a system whose operation is degraded if results are not produced according to the specified timing requirements l A ‘hard’ real-time system is a system whose operation is incorrect if results are not produced according to the timing specification ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 6 Stimulus/Response Systems l Given a stimulus, the system must produce a response within a specified time l Periodic stimuli. Stimuli which occur at predictable time intervals • For example, a temperature sensor may be polled 10 times per second l 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 ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 7 Architectural considerations l 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 l Timing demands of different stimuli are different so a simple sequential loop is not usually adequate l Real-time systems are usually designed as cooperating processes with a real-time executive controlling these processes ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 8 A real-time system model Real-time control system Actuator Actuator Actuator Actuator Sensor Sensor Sensor Sensor Sensor Sensor ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 13 Slide 9 System elements...
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This note was uploaded on 11/09/2009 for the course SE 120336 taught by Professor Unknown during the Spring '09 term at Avila University.

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ch13 - ©Ian Sommerville 2000 Software Engineering, 6th...

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