1. EEL 6897 1 Software development for real-time engineering systems

2. EEL 6897 2 Acknowledgements These lecture slides were adopted from the slides of Andy Wellings

3. EEL 6897 3 Book RTSJ Version 1.0.1

4. EEL 6897 4 Prerequisites You should already: –be a competent programmer in an imperative programming language like C, C++, C# etc –be able to program in sequential Java –have a good understanding of Operating System Principles, in particular the mechanisms needed to support concurrency, e.g. processes, semaphores, etc

5. EEL 6897 5 Overall technical aims of the course To understand the basic requirements of concurrent and real-time systems To be able to create concurrent programs To be able to create advanced concurrent real-time systems

6. EEL 6897 6 Concurrent programming The name given to programming notation and techniques for expressing potential parallelism and solving the resulting synchronization and communication problems Implementation of parallelism is a topic in computer systems (hardware and software) that is essentially independent of concurrent programming Concurrent programming is important because it provides an abstract setting in which to study parallelism without getting bogged down in the implementation details

7. EEL 6897 7 Why we need it To fully utilise the processor 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 10 2 1 -8 10 -9 Response time in seconds 10 0 humantape floppy CD memory processor

8. EEL 6897 8 Parallelism Between CPU and I/O Devices CPUI/O Device Initiate I/O Operation Process I/O Request Signal Completion Interrupt I/O Routine I/O Finished Continue with Outstanding Requests

9. EEL 6897 9 Why we need it (cont’d) To allow the expression of potential parallelism so that more than one computer can be used to solve the problem Consider trying to find the way through a maze

10. EEL 6897 10 Sequential Maze Search

11. EEL 6897 11 Concurrent Maze Search

12. EEL 6897 12 Why we need it (cont’d) To model the parallelism in the real world Virtually all real-time systems are inherently concurrent — devices operate in parallel in the real world This is, perhaps, the main reason to use concurrency

13. EEL 6897 13 Air Traffic Control

14. EEL 6897 14 Why we need it Alternative: use sequential programming techniques The programmer must construct the system as the cyclic execution of a program sequence to handle the various concurrent activities This complicates the programmer's task and involves considerations of structures which are irrelevant to the control of the activities in hand The resulting programs will be more obscure and inelegant Decomposition of the problem is more complex Parallel execution of the program on more than one processor is more difficult to achieve The placement of code to deal with faults is more problematic

15. EEL 6897 15 Terminology A concurrent program is a collection of autonomous sequential processes, executing (logically) in parallel Each process has a single thread of control The actual implementation (i.e. execution) of a collection of processes usually takes one of three forms. Multiprogramming –processes multiplex their executions on a single processor Multiprocessing –processes multiplex their executions on a multiprocessor system where there is access to shared memory Distributed Processing –processes multiplex their executions on several processors which do not share memory

16. EEL 6897 16 What is a real-time system? A real-time system is any information processing system which has to respond to externally generated input stimuli within a finite and specified period –the correctness depends not only on the logical result but also the time it was delivered –failure to respond is as bad as the wrong response! The computer is a component in a larger engineering system => EMBEDDED COMPUTER SYSTEM 99% of all processors are for the embedded systems market

17. EEL 6897 17 Terminology Hard real-time — systems where it is absolutely imperative that responses occur within the required deadline. E.g. Flight control systems. Soft real-time — systems where deadlines are important but which will still function correctly if deadlines are occasionally missed. E.g. Data acquisition system. Firm real-time — systems which are soft real-time but in which there is no benefit from late delivery of service. A system may have all hard, soft and firm real-time subsystems. Many systems may have a cost function associated with missing each deadline

18. EEL 6897 18 A simple fluid control system Pipe Flow meter Valve Interface Computer Time Input flow reading Processing Output valve angle

19. EEL 6897 19 A Grain-Roasting Plant Fuel Tank Furnace Bin Pipe fuel grain

20. EEL 6897 20 A Process Control System Process Control Computer Chemicals and Materials Valve Temperature Transducer Stirrer Finished Products PLANT

21. EEL 6897 21 A Production Control System Production Control System Parts Machine ToolsManipulatorsConveyor Belt Finished Products

22. EEL 6897 22 A Command and Control System Temperature, Pressure, Power and so on Terminals Command and Control Computer Command Post Sensors/Actuators

23. EEL 6897 23 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

24. EEL 6897 24 Characteristics of a RTS Large and complex — vary from a few hundred lines of assembler or C to 20 million lines of Ada estimated for the Space Station Concurrent control of separate system components — devices operate in parallel in the real-world; better to model this parallelism by concurrent entities in the program Facilities to interact with special purpose hardware — need to be able to program devices in a reliable and abstract way

25. EEL 6897 25 Characteristics of a RTS Extreme reliability and safe — embedded systems typically control the environment in which they operate; failure to control can result in loss of life, damage to environment or economic loss Guaranteed response times — we need to be able to predict with confidence the worst case response times for systems; efficiency is important but predictability is essential