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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
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PREREQUISITES
• Basic understanding of Ada and C
• Basic understanding of Computer Architectures.
• Basic understanding of Operating Systems
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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.
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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
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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
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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
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EXAMPLE 1: A SIMPLE FLUID CONTROL SYSTEM
Pipe
Flow meter
Valve
Interface
ComputerTime
Input flow
reading
Processing
Output valve
angle
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APPLICATION EXAMPLE:A GRAIN-ROASTING PLANT
Fuel Tank
Furnace
Bin
Pipe
fuel
grain
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APPLICATIONS: A PROCESS CONTROLSYSTEM
Process
Control
Computer
Chemicalsand
Materials
ValveTemperature
TransducerStirrer
Finished
Products
PLANT
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APPLICATIONS: A PRODUCTIONCONTROL SYSTEM
Production
Control
System
Parts
Machine Tools Manipulators Conveyor Belt
Finished
Products
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COMMAND AND CONTROL SYSTEM
Temperature, Pressure, Power and so on
Terminals
Command and Control
Computer
Command
Post
Sensors/Actuators
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EXAMPLE 2: SISTEMA DE FRENADO ABS
freno
computadorsensor de velocidad
sensor de guiñadaÁngulo de giro
pedal defreno
actuador
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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
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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
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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
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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
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REAL-TIME LANGUAGES AND OSS
Hardware
Operating
System
User Programs
Typical OS Configuration
Hardware
Including Operating
System Components
User Program
Typical Embedded Configuration
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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
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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
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Characteristics
Real-Time
facilitiesConcurrency
Numerical
computation
Interaction
with
hardware
Efficiency/
Predictability
Reliability/
Safety
Large/
Complex
ASPECTS OF REAL-TIME SYSTEMS