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Understanding Real-Time Systems: Design Paradigms and Fault Tolerance

Explore the principles of real-time systems, fault tolerance, and design paradigms with examples like railway operations and telecommunications. Learn about event-triggered and time-triggered systems for critical applications.

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Understanding Real-Time Systems: Design Paradigms and Fault Tolerance

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  1. Real-time systems

  2. Real-time systems • Real-time (RT) Systems • RT transaction Controlled Object Computer System Operator Sensors / Actuators CS351 - Software Engineering (AY2004)

  3. Example Computer System Railway Operator Alpha Engines / Points Ada CS351 - Software Engineering (AY2004)

  4. System design • Finite processing capacity. • Critical Real-time transactions. • Assumptions • Load? • Faults? • Coverage? CS351 - Software Engineering (AY2004)

  5. Load hypothesis • Peak load? • How rare are events? • Do events cascade? CS351 - Software Engineering (AY2004)

  6. Fault hypothesis • Types of faults? • Frequency of faults? • Peak load & maximum fault rate? • Assumption coverage? CS351 - Software Engineering (AY2004)

  7. Hard and soft High Availability Telephone Soft High Integrity Banking RT systems Fail Safe Signalling Hard Fail Operational Flight control CS351 - Software Engineering (AY2004)

  8. Design paradigms • Guaranteed response (GR). • Best-effort. • Most RT systems are best-effort. • Safety critical systems must be GR. CS351 - Software Engineering (AY2004)

  9. Example real-timesystems • Factory automation • open loop, • closed loop. • Telephone switching. • Car control. CS351 - Software Engineering (AY2004)

  10. Fault-tolerance • Fault-tolerant (FT) systems. • Mask or repair errors to avoid faults. • Redundancy • physical, • time, • information. CS351 - Software Engineering (AY2004)

  11. Redundancy • Passive redundancy • fail-silent, • fail-stop. • Active redundancy • voting/concensus, • replica determinism. CS351 - Software Engineering (AY2004)

  12. Event triggered real-time systems • Event oriented execution. • Event showers • random, • sporadic. • Scheduling is dynamic and hard. • Extensible. CS351 - Software Engineering (AY2004)

  13. Time triggered real-time systems • Process events at fixed times. • Overload not handled. • Piority events may be delayed. • Scheduling can be statically determined. • It is hard to extend. CS351 - Software Engineering (AY2004)

  14. TT Example Operator ethernet Event Monitor Command Filter Alpha 9600 bps 2400 bps Trains CS351 - Software Engineering (AY2004)

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