Capítulo01-sistemas en tiempo real

7/27/2019 Capítulo01-sistemas en tiempo real

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Sistemas en Tiempo Real © 2013. H. Mora

Presentación basada en la presentación Chapter 1 del libro “Real-Time Systems and Programming Languages”

SISTEMAS EN TIEMPO REAL

Introducción a los Sistemas de Tiempo Real

1



PREREQUISITES

• Basic understanding of Ada and C

• Basic understanding of Computer Architectures.

• Basic understanding of Operating Systems



OBJETIVOS

• Conocer los conceptos básicos de los Sistemas deTiempo Real

• Conocer las características de un Sistema deTiempo Real.

• Conocer situaciones de aplicación de los Sistemasde Tiempo Real.



WHAT IS A REAL-TIME SYSTEM?

• A real-time system is any information processing systemwhich has to respond to externally generated inputstimuli within a finite and specified period

•

the correctness depends not only on the logical resultbut also the time it was delivered

• failure to respond is as bad as the wrong response!

•

The computer is a component in a larger engineeringsystem => EMBEDDED COMPUTER SYSTEM

• 99% of all processors are for the embedded systemsmarket



CLASIFICACIÓN

• Hard real-time — systems where it is absolutelyimperative that responses occur within the requireddeadline, e.g. A flight control system

• Soft real-time —

systems where deadlines are importantbut which will still function correctly if deadlines areoccasionally 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 single system may have hard, soft and firm real-timesubsystems. In reality many systems will have a cost function

associated with missing each deadline



TERMINOLOGY

• Time-aware — system makes explicit reference totime (eg. open vault door at 9.00)

• Reactive — system must produce output within

deadline (as measured from input)• Required to constraint input and output (time) variability,

input jitter and output jitter control

• Time-triggered — computation is triggered by the

passage of time• Release activity at 9.00

• Release activity every 25ms – a periodic activity

• Event-trigger — computation is triggered by an

external or internal event



EXAMPLE 1: A SIMPLE FLUID CONTROL SYSTEM

Pipe

Flow meter

Valve

Interface

ComputerTime

Input flow

reading

Processing

Output valve

angle



APPLICATION EXAMPLE:A GRAIN-ROASTING PLANT

Fuel Tank

Furnace

Bin

Pipe

fuel

grain



APPLICATIONS: A PROCESS CONTROLSYSTEM

Process

Control

Computer

Chemicalsand

Materials

ValveTemperature

TransducerStirrer

Finished

Products

PLANT



APPLICATIONS: A PRODUCTIONCONTROL SYSTEM

Production

Control

System

Parts

Machine Tools Manipulators Conveyor Belt

Finished

Products



COMMAND AND CONTROL SYSTEM

Temperature, Pressure, Power and so on

Terminals

Command and Control

Computer

Command

Post

Sensors/Actuators



EXAMPLE 2: SISTEMA DE FRENADO ABS

freno

computadorsensor de velocidad

sensor de guiñadaÁngulo de giro

pedal defreno

actuador



A TYPICAL EMBEDDED SYSTEM

Algorithms for

Digital Control

Data Logging

Data Retrievaland Display

Operator

Interface

InterfaceEngineering

System

Remote

Monitoring System

Real-Time

Clock

Database

Operator’s

Console

DisplayDevices

Real-Time Computer



CHARACTERISTICS OF A RTS

• Guaranteed response times — we need to be able topredict with confidence the worst case response timesfor systems; efficiency is important but predictability isessential

• Concurrent control of separate system components — devices operate in parallel in the real-world; better tomodel this parallelism by concurrent entities in theprogram

• Facilities to interact with special purpose hardware — need to be able to program devices in a reliable andabstract way



CHARACTERISTICS OF A RTS

• Support for numerical computation – be able to supportthe discrete/continuous computation necessary forcontrol system feed-back and feed-forward algorithms

• Large and complex — vary from a few hundred lines ofassembler or C to 20 million lines of Ada, also variety aswell as size is an issue

• Extreme reliability and safety — embedded systemstypically control the environment in which they operate;failure to control can result in loss of life, damage toenvironment or economic loss



RT PROGRAMMING LANGUAGES

• With operating system support• Assembly languages

• Sequential systems implementation languages — e.g. RTL/2,Coral 66, Jovial, C.

• No operating system support!

• High-level concurrent languages. e.g. Ada, Java, Pearl,Modula-2.

• We will consider:• Java/Real-Time Java

• C and Real-Time POSIX (not in detail)

• Ada 2005



REAL-TIME LANGUAGES AND OSS

Hardware

Operating

System

User Programs

Typical OS Configuration

Hardware

Including Operating

System Components

User Program

Typical Embedded Configuration



SUMMARY

• This lecture has introduced a number of keydefinitions and examples of real-time

systems

• The basic aspects of a real-time are well

represented in the following diagrams



ASPECTS OF REAL-TIME SYSTEMS

Real-Time

Temporal

RequirementsStructure Classification

Characteristics

(see next page)

Deadline/

Latency

Input/output

jitter

Periodic/

Sporadic/

Aperiodic

Time-

triggered

Event-

triggeredCriticality

Role of

time

hard time-aware

reactivesoft

firm



Characteristics

Real-Time

facilitiesConcurrency

Numerical

computation

Interaction

with

hardware

Efficiency/

Predictability

Reliability/

Safety

Large/

Complex

ASPECTS OF REAL-TIME SYSTEMS

Capítulo01-sistemas en tiempo real

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