1. Real-time systems

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

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

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

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

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

7. CS351 - Software Engineering (AY2004)7 Hard and soft RT systems Soft Hard High AvailabilityTelephone High IntegrityBanking Fail SafeSignalling Fail OperationalFlight control

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

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

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

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

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

13. 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.

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