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

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

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

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

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

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

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

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

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

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

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

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

Implementation Example 4.6 in Other Material

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

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

Architecture Interfaces Model UserInterface SubsystemInterface Platform OSFileSystem Functions...

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

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