ist 37652 hard real-time corba hrtc hrtc final review, lund 16 september, 2003 wp1: corba control...

HRTC Final Review, Lund 16 September, 2003

IST 37652 Hard Real-time CORBA

HRTC

WP1: CORBA Control SystemsWP1: CORBA Control Systems

Karl-Erik Årzén & Ricardo Sanz

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Final Review, Lund, 16 September, 2003

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IST 37652 / Hard Real-time CORBA

Main Activities and AchievementsMain Activities and Achievements

• Domain-analysis of CORBA Control Systems Domain-analysis of CORBA Control Systems completedcompleted

• D1.1 acceptedD1.1 accepted

• Domain architectures for CORBA Control Domain architectures for CORBA Control SystemsSystems

• CORBA control design patternsCORBA control design patterns• D1.2 final version, pending approvalD1.2 final version, pending approval

• CORBA Control System Engineering Handbook CORBA Control System Engineering Handbook • D1.3 to be sent at the end of the projectD1.3 to be sent at the end of the project

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Main Activities and AchievementsMain Activities and Achievements

• Simulation tools for CORBA-based Simulation tools for CORBA-based networked control loops:networked control loops:• TrueTime simulation toolbox extendedTrueTime simulation toolbox extended

• Switched EthernetSwitched Ethernet• Multiple EthernetsMultiple Ethernets• Extra deliverable on TrueTime/Jitterbug for Extra deliverable on TrueTime/Jitterbug for

CORBA (HRTC057) will be completed and CORBA (HRTC057) will be completed and updated (sent at the end of the project)updated (sent at the end of the project)



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Domain AnalysisDomain AnalysisDeliverable 1.1

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D1.1 Domain Analysis of CORBA D1.1 Domain Analysis of CORBA Control SystemsControl Systems

1.1. IntroductionIntroduction2.2. Distributed Objects and CORBADistributed Objects and CORBA

• CORBACORBA• RT-CORBART-CORBA• Competing TechnologiesCompeting Technologies• What is needed for HRT CORBA?What is needed for HRT CORBA?

3.3. Components in Control SystemsComponents in Control Systems• Domain desctiptionsDomain desctiptions• CORBA and component examplesCORBA and component examples

4.4. CORBA Control LoopsCORBA Control Loops• Loop TimingLoop Timing• Effects of delaysEffects of delays• TrueTime and Jitterbug for analysis and simulationTrueTime and Jitterbug for analysis and simulation

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CORBA in Control SystemsCORBA in Control Systems

Strategic ControlStrategic Control

Complex LoopsComplex Loops

Advanced ControlAdvanced Control

Operational ControlOperational Control

Tactical ControlTactical Control

Sensors & ActuatorsSensors & Actuators

Simple LoopsSimple Loops

MISMIS

PlantPlant

Optimization

Plan execution

Reactivity

Conventional Process Control

User

Inte

rface

User

Inte

rface

• CORBA:• well-suited• concept proved in other projects

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HRTC FocusHRTC Focus

Strategic ControlStrategic Control

Complex LoopsComplex Loops

Advanced ControlAdvanced Control

Operational ControlOperational Control

Tactical ControlTactical Control

Sensors & ActuatorsSensors & Actuators

Simple LoopsSimple Loops

MISMIS

PlantPlant

Optimization

Plan execution

Reactivity

Conventional Process Control

User

Inte

rface

User

Inte

rface The aim of HRTC

• where the hard r-t constraints are found

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What do we mean by What do we mean by ”Hard” Real-Time?”Hard” Real-Time?

• Minimum requirement:Minimum requirement:• Maximum bound on network end-to-end Maximum bound on network end-to-end

latencylatency• It is assumed that the RT-CORBA technology It is assumed that the RT-CORBA technology

used is able provide the corresponding used is able provide the corresponding guarantees on the client and server sidesguarantees on the client and server sides

• Additional requirements:Additional requirements:• Minimum bound on the network latencyMinimum bound on the network latency• Minimum jitter on the network latencyMinimum jitter on the network latency

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Are Control Systems Hard of Soft?Are Control Systems Hard of Soft?

• Depends on application.Depends on application.• Most control systems are relatively robust against delays Most control systems are relatively robust against delays

and jitter.and jitter.• For safety-critical systems the hard real-time model has For safety-critical systems the hard real-time model has

many advantagesmany advantages• VerificationVerification• Time-triggered approaches that minimizes jitter are well suited, Time-triggered approaches that minimizes jitter are well suited,

e.g., TTA/TTPe.g., TTA/TTP

• Most “hard” real-time control applications are not safety-Most “hard” real-time control applications are not safety-criticalcritical

• Less deterministic approaches work well, e.g., event-triggered Less deterministic approaches work well, e.g., event-triggered implementation methods that only give upper bounds on latencyimplementation methods that only give upper bounds on latency

• E.g., in automation and roboticsE.g., in automation and robotics

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HRT-CORBA General RequirementsHRT-CORBA General Requirements

• Deterministic TransportsDeterministic Transports• IIOP one of the main sources of nondeterminism in IIOP one of the main sources of nondeterminism in

CORBA/RT-CORBACORBA/RT-CORBA• Different applications need different levels of Different applications need different levels of

determinismdeterminism• Periodic requestsPeriodic requests

• Sender – Reciever model Sender – Reciever model • IDL support for representing periodic requests IDL support for representing periodic requests

• information that concerns both the client and the server information that concerns both the client and the server object as a single entityobject as a single entity

• associate timing attributes to this entity, e.g., the period, the associate timing attributes to this entity, e.g., the period, the amount of data that will transferred, and what the maximum amount of data that will transferred, and what the maximum allowed communication latency isallowed communication latency is

• RT-CORBA activities not enoughRT-CORBA activities not enough

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• Scheduling supportScheduling support• Network is a shared resource that needs scheduled accessNetwork is a shared resource that needs scheduled access• Also applies to client and server-side computations if a time-Also applies to client and server-side computations if a time-

triggered approach is adoptedtriggered approach is adopted• Scheduling of distributable threads (RT-CORBA 2.0 Scheduling of distributable threads (RT-CORBA 2.0

specification) a possible solutionspecification) a possible solution• Global location for scheduling informationGlobal location for scheduling information• Implemented as CORBA service or as a special CORBA objectImplemented as CORBA service or as a special CORBA object• The scheduling support in RT-CORBA not enoughThe scheduling support in RT-CORBA not enough

• Small footprintSmall footprint• Hard real-time often needed in embedded systems with limited Hard real-time often needed in embedded systems with limited

resourcesresources• HRT-CORBA ought to build upon Minimum CORBA rather than HRT-CORBA ought to build upon Minimum CORBA rather than

RT-CORBART-CORBA

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• DeadlinesDeadlines• Deadline-based representations more natural Deadline-based representations more natural

than priority-based for many hard real-time than priority-based for many hard real-time applicationsapplications

• RT-CORBA 2.0 specificationRT-CORBA 2.0 specification

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HRT CORBA threatsHRT CORBA threats

• Industrial control systems are in general Industrial control systems are in general based on Microsoft technologiesbased on Microsoft technologies• COM/DCOM/.NET/OPC technologies are COM/DCOM/.NET/OPC technologies are

strongly favouredstrongly favoured

• CORBA is by many considered as a too CORBA is by many considered as a too complex technology for embedded complex technology for embedded applicationsapplications

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Clarification from Midterm ReviewClarification from Midterm Review

• How is the control-related timing issues How is the control-related timing issues reflected in HRT CORBA?reflected in HRT CORBA?• Timestamped messagesTimestamped messages• Described in D 2.2Described in D 2.2• Not tested yetNot tested yet



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Domain ArchitecturesDomain ArchitecturesDeliverable 1.2

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The Process of DesingThe Process of Desing• Modern control systems are very Modern control systems are very complex applicationscomplex applications

that pose special difficulties to systems designersthat pose special difficulties to systems designers

• Design Design knowleddge transferknowleddge transfer is difficult at the is difficult at the architectural level architectural level

• Recurring designs Recurring designs are common in the field of automatic are common in the field of automatic control but in most cases their documentation formats control but in most cases their documentation formats are restricted to small subfields of applicationare restricted to small subfields of application

• Control systems designs are heterogeneous and Control systems designs are heterogeneous and multidisciplinarymultidisciplinary by nature by nature

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Views on ArchitectureViews on Architecture

• Documenting Documenting domain architecturesdomain architectures• Domain Specific Software ArchitecturesDomain Specific Software Architectures• Technical ArchitecturesTechnical Architectures• FrameworksFrameworks• PatternsPatterns

• Design patternsDesign patterns are the selected are the selected alternative for D1.2alternative for D1.2

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Patterns and SchemataPatterns and Schemata

• In this report we propose a In this report we propose a pattern schemapattern schema with with two particular properties:two particular properties:

• it specifically deals with some issues very relevant to it specifically deals with some issues very relevant to control designerscontrol designers

• it is generic enough to gather under the same it is generic enough to gather under the same umbrella an heterogeneous collection of patterns umbrella an heterogeneous collection of patterns ranging from basic, elementary control and/or ranging from basic, elementary control and/or software components to plant-wide systems. software components to plant-wide systems.

• This schema is being used in the implementation This schema is being used in the implementation of a of a pattern languagepattern language for the construction of for the construction of control systems.control systems.

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What are design patterns?What are design patterns?

• Established ways of Established ways of solving design problemssolving design problems• Distilled Distilled know-know-hhowow of previous work of previous work• Documented in Documented in usable formatsusable formats (pattern schemas) (pattern schemas)• Organised in Organised in pattern languagespattern languages• Can be composedCan be composed

• Examples in all engineering field:Examples in all engineering field:• Chemical: Distillation UnitChemical: Distillation Unit• Civil: Suspension BridgeCivil: Suspension Bridge• Aeronautic: TriplaneAeronautic: Triplane

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Cascade ControlCascade Control

PID 2PID 2PID 1PID 1

A/D

A/D

Yref

Y

UU

Yref

Y

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Abstract Cascade ControlAbstract Cascade Control

Control-2Control-2Control 1Control 1

A/D

A/D

Yref

Y

UU

Yref

Y

Cascading Cascading is a design patternis a design pattern

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ControllerController

ControllerController ActuatorActuatorSensorSensor

StateState ActionAction

WorldWorld

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TunerTuner


TunerTuner

PerformancePerformance ParametersParameters

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Tuned ControllerTuned Controller

ActuatorActuatorSensorSensor

TunerTuner

PerformancePerformance ParametersParameters


StateState ActionAction

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Pattern LanguagesPattern Languages

• Pattern languages are Pattern languages are collections of patternscollections of patterns for for a domaina domain

• ““The sequential and organic structure of The sequential and organic structure of patterns for a specific application domain patterns for a specific application domain becomes the method for the development becomes the method for the development process”process”

• Designs are produced by Designs are produced by pattern combinationpattern combination• A pattern language can be A pattern language can be generativegenerative

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Pattern DocumentationPattern Documentation

• Using a Using a pattern schemapattern schema::• Many available: GOF, Alexandrian, etc.Many available: GOF, Alexandrian, etc.• Domain-specific formatDomain-specific format

• Typical Contents:Typical Contents:• Name, Problem, Context, Forces, Solution, Name, Problem, Context, Forces, Solution,

Example, etc.Example, etc.

• CCS Pattern SchemaCCS Pattern Schema

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CCS Pattern SchemaCCS Pattern Schema

• NameName• AliasesAliases• ExampleExample• ProblemProblem• SolutionSolution• ForcesForces• ContextContext• Structure Structure • DynamicsDynamics

• ImplementationImplementation• TimingTiming• Example resolvedExample resolved• VariantsVariants• Known UsesKnown Uses• Consequences Consequences • Related withRelated with• ReferencesReferences

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CCS PatternsCCS Patterns

• Just a first step in a pattern language for Just a first step in a pattern language for CCSCCS

• Some patterns in the document:Some patterns in the document:• Active ObjectActive Object• Pluggable transportPluggable transport• Networked Control Loop PatternNetworked Control Loop Pattern• Controller Function Block PatternController Function Block Pattern• Distributed Control SystemDistributed Control System



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Networked Control LoopNetworked Control LoopAn Example

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NameName

• Networked Control LoopNetworked Control Loop

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AliasesAliases

• CORBA control loopCORBA control loop

• Distributed control loopDistributed control loop

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ExamplesExamples

• Networked control loops are becoming increasingly Networked control loops are becoming increasingly important in a number of application areas. important in a number of application areas.

• One major example is automotive systems where One major example is automotive systems where sensors and actuators often are located closely to the sensors and actuators often are located closely to the physical devices which they sense/actuate. physical devices which they sense/actuate.

• The control loops are closed over some data bus, e.g., The control loops are closed over some data bus, e.g., CAN, TTCAN, Flexray, or TTP. CAN, TTCAN, Flexray, or TTP.

• Another example is process automation where actuators Another example is process automation where actuators and sensors often are distributed in the plant, and sensors often are distributed in the plant, communicating with the control system using a fieldbus, communicating with the control system using a fieldbus, e.g. ProfiBus, Foundation, etc., e.g. ProfiBus, Foundation, etc.,

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ProblemProblem

• A dynamical physical system with input(s) A dynamical physical system with input(s) through which one may influence it using through which one may influence it using actuator(s), and output(s) through which can actuator(s), and output(s) through which can measure its performance using sensor(s), has measure its performance using sensor(s), has poor performance and robustness, and is poor performance and robustness, and is negatively affected by disturbances acting on negatively affected by disturbances acting on the system.the system.

• The sensors and actuators are physically The sensors and actuators are physically separated from each other.separated from each other.

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SolutionSolution

• Increase the robustness and performance of a Increase the robustness and performance of a system through feedback control implemented in system through feedback control implemented in a separate controller node.a separate controller node.

• Reject disturbances acting on the systems Reject disturbances acting on the systems through feedback.through feedback.

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StructureStructure

• Each of the three nodes support CORBAEach of the three nodes support CORBA

• The functionality of the three nodes is The functionality of the three nodes is realised using CORBA objects. realised using CORBA objects.

Controllernode

Actuatornode

Measurement(s) Control signal(s)

Sensornode

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DynamicsDynamics

• The dynamics of the pattern depends primarily The dynamics of the pattern depends primarily on two things: on two things:

• whether an information-push or an information-pull whether an information-push or an information-pull model is used, and model is used, and

• whether the interactions are one-way invocations whether the interactions are one-way invocations without any return message or if they are ordinary, without any return message or if they are ordinary, two-way, CORBA request-reply invocations.two-way, CORBA request-reply invocations.

• In the basic, and most simple version of the In the basic, and most simple version of the pattern we assume that information-push is used pattern we assume that information-push is used both from the sensor to the controller and from both from the sensor to the controller and from the controller to the actuator. the controller to the actuator.

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ImplementationImplementation

• The pattern can be implemented using CORBA, The pattern can be implemented using CORBA, RT-CORBA, or HRT-CORBA. The main RT-CORBA, or HRT-CORBA. The main difference between these alternatives concerns difference between these alternatives concerns level of determinism achieved level of determinism achieved

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TimingTiming

• Closing a control loop over a network gives rise Closing a control loop over a network gives rise to communication delays. to communication delays.

• These delays affect the performance of the These delays affect the performance of the controller negatively. controller negatively.

• From a control point of view it is desirable to From a control point of view it is desirable to have constant sampling delay and short input-have constant sampling delay and short input-output latency. output latency.

• If the input-output latency is constant, it can If the input-output latency is constant, it can easily be compensated for. However, it is easily be compensated for. However, it is general better to have a short latency with jitter general better to have a short latency with jitter than a longer, but constant, latency.than a longer, but constant, latency.



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Engineering HandbookEngineering HandbookD 1.3

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StructureStructure

• Part 1: Overview and introductory materialPart 1: Overview and introductory material• This part sets the stage fro what comes after.This part sets the stage fro what comes after.

• Part 2: OMG Technology Part 2: OMG Technology • This part describes available OMG specifications that are of This part describes available OMG specifications that are of

relevance for the construction of CORBA-based control systems.relevance for the construction of CORBA-based control systems.• Part 3: CORBA ProductsPart 3: CORBA Products

• This part describes available products and tools that are of This part describes available products and tools that are of relevance for the construction of CORBA-based control systems.relevance for the construction of CORBA-based control systems.

• Part 4: A Core MethodologyPart 4: A Core Methodology• This part describes a basic methodology to be used in the This part describes a basic methodology to be used in the

construction of CORBA-based controllers.construction of CORBA-based controllers.• Part 5: Additional MaterialsPart 5: Additional Materials

• This part gathers useful heterogeneous material that cannot be This part gathers useful heterogeneous material that cannot be cleanly placed in the other parts.cleanly placed in the other parts.

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11 IntroductionIntroduction22 GlossaryGlossary

33 CORBACORBA44 RT-CORBART-CORBA55 Embedded & Fault-tolerantEmbedded & Fault-tolerant66 UMLUML77 CCMCCM88 Domain SpecificationsDomain Specifications

99 ORBsORBs1010 Design ToolsDesign Tools1111 PlatformsPlatforms

1212 Methodological ApproachMethodological Approach1313 Basic processesBasic processes1414 Early requirementsEarly requirements1515 Late requirementsLate requirements1616 Architectural designArchitectural design1717 Detailed designDetailed design1818 ImplementationImplementation

1919 Common pitfallsCommon pitfalls2020 Engineering for qualityEngineering for quality

2121 ReferencesReferences

Part 1:Part 1: Introductory material Introductory material

Part 2Part 2: OMG Specifications: OMG Specifications

Part 3:Part 3: Software Products Software Products

Part 4:Part 4: Methodology Methodology

Part 5:Part 5: Additional Materials Additional Materials

AppendicesAppendices

HRTC Final Review, Lund 16 September, 2003 42


HRTC

Analysis and Simulation of CORBA Networked Control Loops

Analysis and Simulation of CORBA Networked Control Loops

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TrueTime and JitterbugTrueTime and Jitterbug

SchedulingParameters

(T,D,Prio, …)

Loop TimingParameters

(latencies, jitter, …)

ControlPerformance

(variance, rise time, overshoot, ….)

Complex, ”nonlinear”relationship

Non-trivialrelationship

Simulation withTrueTime

Analysis withJitterbug

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TrueTimeTrueTime

• Simulation of networked control loops Simulation of networked control loops under shared computing resources under shared computing resources

• Co-simulation of controller task execution, Co-simulation of controller task execution, network transmissions, and continuous network transmissions, and continuous plant dynamics plant dynamics

• Developed by Anton Cervin, Dan Developed by Anton Cervin, Dan Henriksson, Johan Eker Henriksson, Johan Eker

• Simulink-basedSimulink-based

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Computer BlockComputer Block

• Fixed priority• EDF• Static schedule• User defined

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Network BlockNetwork Block

TCP transport added

link-layer

• Switched Ethernet• Multiple networks

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TrueTime and CORBATrueTime and CORBA

• Comparative simulations of CORBA control loopsComparative simulations of CORBA control loops• CORBA (IIOP (TCP)) – demonstrated at mid-review meetingCORBA (IIOP (TCP)) – demonstrated at mid-review meeting• RT-CORBA (IIOP (TCP))RT-CORBA (IIOP (TCP))

• Server-declared vs client-propagated prioritiesServer-declared vs client-propagated priorities• Thread pools and thread lanesThread pools and thread lanes• MutexesMutexes

• HRT-CORBAHRT-CORBA• Switched Ethernet transport -- DEMOSwitched Ethernet transport -- DEMO

• Switch buffer sizeSwitch buffer size

• ThrottleNetThrottleNet• Traffic controlTraffic control

• TTP TransportTTP Transport• TDMA datalinkTDMA datalink

• Simulation results relative rather than absoluteSimulation results relative rather than absolute

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DEMO

Anton Cervin

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ist 37652 hard real-time corba hrtc hrtc final review, lund 16 september, 2003 wp1: corba control...

Documents

corba hrtc057

hrt corba

networked control loops

corba corbacorba rtcorbart

hrtc consortium

simulation slide

final version

domain analysis deliverable