1. Real-Time Systems – The big Picture
ITV Real-Time Systems
Anders P. Ravn
Aalborg University
February 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
Interface
Input flow
reading
Flow meter
Processing
Valve
Output valve
angle
Computer

7. The Control Task Periodic: OR Sporadic: LOOP LOOP wait_until(t)
read_sensor;
compute;
write_actuator;
t = t+T;
END
LOOP
wait_event;
read_sensor;
compute;
write_actuator;
END

8. The R-T Constraint The activation times Si and response times Ri
satisfy:
Ri – Si  D – the deadline
Si+1 – Si = T – the period

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

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

11. A Simple Embedded System
Thermocouples
ADC
Pressure
Transducer T S P
Switch
ADC
Heater
Screen
DAC
Pump/Valve
Keep the temperature and pressure of some chemical process within well-defined limits

12. Implementation
See Example 7.6 in Other Material

13. 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

14. RTS Implementation Language characteristics: Security Readability
Flexibility
Simplicity
Portability
Efficiency

15. Validation Verification Testing Simulation Model
Prototype with Test harness
Real System ON

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