tailieunhanh - Scheduling in RealTime Systems

In real-time applications, the timing requirements a re the main c onstraints a nd their mastering is the predominant factor for a ssessing the quality of service. Timing con-straints span many application a reas, suc h a s industrial plant automation, embedded systems, vehicle control, nuclear plant monitoring, scientific e xperiment guidance, robotics, multimedia audio a nd video str eam conditioning, surgical operation moni-toring, and stock exchange orders follow-up. Applications trigger periodic or r andom events and r equire that the a ssociated com-puter system reacts before a given delay or a fixed time. The timing latitude to react is limited since transient data must. | Scheduling in Real-Time Systems. Francis Cottet Joelle Delacroix Claude Kaiser and Zoubir Mammeri Copyright 2002 John Wiley Sons Ltd. ISBN 0-470-84766-2 1 Basic Concepts Real-Time Applications Real-time applications issues In real-time applications the timing requirements are the main constraints and their mastering is the predominant factor for assessing the quality of service. Timing constraints span many application areas such as industrial plant automation embedded systems vehicle control nuclear plant monitoring scientific experiment guidance robotics multimedia audio and video stream conditioning surgical operation monitoring and stock exchange orders follow-up. Applications trigger periodic or random events and require that the associated computer system reacts before a given delay or a fixed time. The timing latitude to react is limited since transient data must be caught actions have a constraint on both start and finish times and responses or commands must be sent on time. The time scale may vary largely its magnitude being a microsecond in a radar a second in a human-machine interface a minute in an assembly line or an hour in a chemical reaction. The source of timing constraints leads to classifying them as hard or soft. A real-time system has hard timing constraints when a timing fault missing a deadline delivering a message too late sampling data irregularly too large a scatter in data supposed to be collected simultaneously may cause some human economic or ecological disaster. A real-time system has soft timing constraints when timing faults can be dealt with to a certain extent. A real-time computer system is a computer system whose behaviour is fixed by the dynamics of the application. Therefore a real-time application consists of two connected parts the controlling real-time computer system and the controlled process Figure . Time mastery is a serious challenge for real-time computer systems and it is often misunderstood. The .