1. Real-Time Systems – The Big Picture Real-Time Systems Anders P. Ravn Aalborg University September 2009

2. Literature Alan Burns and Andy Wellings: Real-Time Systems: Ada 95, Real-Time Java and Real-Time POSIX (B & W) Acknowledgement: Some slides are adapted from their Teaching Aids

3. Prerequisites Basic understanding of C and Java Basic understanding of Computer Architectures. Basic understanding of Operating Systems

4. Course Aims Understanding of the broad concepts Practical understanding for industry To stimulate research interest

5. What is a real-time system? A real-time system is a computerized system that must respond to externally generated input within specified time bounds The computer is a component in a larger engineering system - EMBEDDED COMPUTER SYSTEM 99% of all processors are for the embedded systems market

6. A simple fluid control system Pipe Flow meter Valve Interface Computer Input flow reading Processing Output valve angle

7. The Program Architecture Meter read(int) Valve write(int) Task

8. The Control Task LOOP wait_until(t); meter.read(y); compute(y,u); valve.write(u); t = t+T; END Periodic: OR Sporadic: LOOP wait_event(); meter.read(y); compute(y,u); valve.write(u); END

9. The R-T Constraint Activation times S i and response times R i satisfy: R i – S i  D – the deadline S i+1 – S i = T – the period

10. Terminology Hard real-time Soft real-time Firm real-time Value of response Time D D D may be missed occasionally Time D

11. Another Example:Steam Boiler 209 Heater (on/off) Pressure (p) 148 Temperature (t) Valve (0..5) Objective: Keep t and p within defined limits

12. The Program Architecture Valve/ Pump Pressure T-task HeaterLog_ Device Temperature P-taskLogger HeatOnTempPressValveSet

13. Implementation Example 4.6 in Other Material

14. A Typical Embedded System Algorithms for Digital Control Data Logging Data Retrieval and Display Operator Interface Engineering System Remote Monitoring System Real-Time Clock Database Operator’s Console Display Devices Real-Time Computer

15. RTS Design Essentially: Specification of a collection of periodic and sporadic tasks. Tasks may share resources, but must not block explicitly. Formalisms: UML-RT RT- HOOD

16. Architecture Interfaces Model UserInterface SubsystemInterface Platform OSFileSystem Functions...

17. Validation 1.Verification 2.Testing 3.Simulation ON 1.Model 2.Prototype with Test harness 3.Real System

18. Characteristics of a RTS Timing Constraints Dependability Requirements Concurrent control of separate components Facilities to interact with special purpose hardware