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Software development for real-time engineering systems

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Acknowledgements

• These lecture slides were adopted from the slides of Andy Wellings

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Book

RTSJ Version 1.0.1

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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

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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

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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

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Why we need it

• To fully utilise the processor

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Parallelism Between CPU and I/O DevicesCPU I/O Device

Initiate I/OOperation Process I/O

Request

Signal Completion

Interrupt I/ORoutine I/O Finished

Continue withOutstanding Requests

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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

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Sequential Maze Search

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Concurrent Maze Search

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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

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Air Traffic Control

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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

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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

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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

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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

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A simple fluid control systemPipe

Flow meter

Valve

Interface

ComputerTime

Input flowreading

Processing

Output valveangle

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A Grain-Roasting Plant

Fuel TankFurnace

Bin

Pipe

fuel

grain

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A Process Control SystemProcessControl

Computer

ChemicalsandMaterials

Valve TemperatureTransducer Stirrer Finished

Products

PLANT

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A Production Control System

ProductionControlSystem

Parts

Machine Tools Manipulators Conveyor Belt

FinishedProducts

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A Command and Control System

Temperature, Pressure, Power and so on

Terminals

Command and ControlComputer

CommandPost

Sensors/Actuators

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A Typical Embedded System

Algorithms forDigital Control

Data Logging

Data Retrievaland Display

OperatorInterface

Interface EngineeringSystem

RemoteMonitoring System

Real-TimeClock

Database

Operator’sConsole

Display Devices

Real-Time Computer

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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

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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