©SCILabs 2002 Real-Time CORBA ©SCILabs Ingenieros S.L. 2002 Miguel Segarra José Antonio Clavijo...

©SCILabs 2002

www.SCILabs.es

Real-Time CORBA

©SCILabs Ingenieros S.L. 2002 www.SCILabs.es

Miguel SegarraJosé Antonio Clavijo

HRTC

Vienna Plenary Meeting

©SCILabs 2002

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Speech Contents

• Introduction• Real-Time/Minimum CORBA

development• The DOTS Project• Conclusions

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Introduction

• What is CORBA?• Useful URLs

Introduction RT CORBA Dev. DOTS Project Conclusions

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What is CORBA

• It is an specification of the OMG

• CORBA specifies an architecture for building distributed object systems, common services for those systems and protocols for interoperability among CORBA implementations.


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What is CORBA? Introduction RT CORBA Dev. DOTS Project Conclusions

HorizontalCORBA Facilities

Object Request Broker

CORBA Services

VerticalCORBA Facilities

ApplicationObjects

• The CORBA “software bus”

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What is CORBA?

UMLModeling CORBAservices

CORBAfacilities

Business Object Facility

Common Business Objects

CORBADomains

CORBADomains

CORBADomains

Me

ta-O

bje

ct F

aci

lity

SE

CU

RIT

Y

IDL Interfaces, Mappings, & ORB

Realtime, Embedded options

Interoperability: IIOP, Asynch

Components, Scripting


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What is CORBA?

• How does it work? Introduction RT CORBA Dev. DOTS Project Conclusions

•Server Side•Client Side

Object Request BrokerIDL

IDL

POA

CLIENT

SERVANT

IDL

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What is CORBA?


IDL

POA

CLIENT

SERVANT


• How does it work?

Client.GetValue(); Servant.GetValue();

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What is CORBA?


IDL

POA

CLIENT

SERVANT


IDL

POA

CLIENT

SERVANT


GIOP

Client.GetValue();

Servant.GetValue();

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Useful URLs

• Our Home Page:– http://www.scilabs.es

• OMG Home Page:– http://www.omg.org

• OMG Specs:– http://www.omg.org/technology/

documents/spec_catalog.htm

• OMG News:– http://www.omg.org/news

• Lots of OO/CORBA URLs– http://www.cetus-links.org


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Speech Contents


Development• The DOTS Project• Conclusions

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RT/Minimum CORBA Development

• CORBA features for real-time/embedded development

• Specifications vs. Reality• RT CORBA Tools for System

Design• Some Lessons Learnt• Industry Trends


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Real-Time/Minimum CORBA Features

• Characteristics of RT CORBA systems– End-to-end system predictability

(not high performance)– Allocation of resources

• Characteristics of Minimum CORBA systems– Limited resources– Full CORBA interoperability


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• End-to-end predictability– Respecting thread priorities

between clients and servers– Bounding the duration of thread

priority inversion– Bounding latencies of operation

invocations


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• Management of resources– Process, storage and

communication• Threadpools• Priorities• Number of concurrent requests• Transport connections


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• Real-Time CORBA 1.0 addresses fixed-priority real-time systems– Priority-based scheduling rather

than e.g. deadline based

• Real-Time CORBA 2.0 addresses dynamic scheduling


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• Minimum CORBA defines a cut down profile of CORBA

• Dynamic aspects of CORBA are removed


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Real-Time CORBA

Specifications vs. Reality


Messaging

CORBA

MinimumCORBA

TimeService

But close to the process resources are very limited!

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Specifications vs. Reality


CORBA

MinimumCORBA

Real-Time CORBA

Messaging

TimeService

Dynamic part of CORBA

In embedded/real-time systems a lot of decisions are made at design time!

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Stub

Client

Real-Time CORBA Tools For System Design


threadpriority

Provide predictability by controlling ORB behavior

ORB

connection

ORBInvoke priority

protocol

Skeleton

POA

threadpriority

concurrency

Servant

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Stub

Client



Impact on ORB architecture of predictability issues

ORB

buffering

ORBdelay

Skeleton

POA

threaddispatching

Servant

buffering

request dispatchingmarhalling

marhalling

Memory mgmt

Memory mgmt

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• Real-time CORBA features– RT ORB and RT POA– RT CORBA priority and priority mappings– RT CORBA priority models– Priority transforms– RT CORBA mutex– Threadpools– Connection management– Protocol selection– Invocation timeout– Bounding of ORB priorities


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• RTCORBA::RTORB– It is an extension of the

CORBA::ORB with operations to create new real-time entities (e.g. threadpool, mutex and new RT policies)

• RTPortableServer::POA– Add to the PortableServer::POA

operations to set priority on an object reference basis


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0

RTCORBA::Priority31

0

31

0

255

OS #1 native priority model

4

25

OS #2 native priority model

Real-Time CORBA Priority

•An OS independent priority scheme. The same range of CORBA priorities for all platforms. Custom priority mappings are allowed.

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Real-Time CORBA Tools For System Design• Real-Time CORBA Priority

Models– Client propagated– Server declared– Per object reference basis


Stub

Client

ORB ORB

Skeleton

POA

Servant

What is the invocationPriority?

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• Client propagated priority model


Stub

Client

ORB ORB

Skeleton

POA

Servant

client running at priority 100Invocation executed at priority 100

Client’s priority propagated along the path to server in a

service context

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• Server declared priority model


Stub

Client

ORB ORB

Skeleton

POA

Servant

client running at priority 100Invocation executed at priority 3347

Client’s priority IS NOT propagated along the path to

server in a service context

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• Priority transforms– Inbound– Outbound


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• Real-Time CORBA mutex– An API to give access to the

mutex implementation that the ORB uses

– This gives consistency to the priority protocol used

– Basic tool for resource protection


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• Threadpools– Server-side tool to handle

invocations– Provide concurrency control– Allows thread pre-creation and reuse– Setup of idle threads priority

• Two flavors of threadpools– Without lanes– With lanes


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• Threadpools Introduction RT CORBA Dev. DOTS Project Conclusions

POA A POA B

ORB

threadpool

POA A POA B

ORB

Threadpool A Threadpool B

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• Threadpools Introduction RT CORBA Dev. DOTS Project Conclusions

Threadpool

Threadpool

Lane A Lane B

•Without lanes- stacksize 512- prio 100- Static 5- Dynamic 3- Req buff Yes- Max Reqs 3- Req Buf Sz 5120

•With lanes- Stacksize 512- Lanes 2- Borrowing Yes- Req buff Yes- Max Reqs 3- Req Buf Sz 5120-Lane A

-Prio 1110-Static 2-Dynamic 1

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• Handling connections– Implicit and explicit binding– Multiplexed connections– Private connections– Banded connections

Introduction RT CORBA Dev.DOTS Project Conclusions

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ORB ORB

client

client client

clientserver

Multiplexed:Resource contention by shared connection

ORB ORB

client

client client

clientserver

Private connection:Exclusive use of a connection by a client


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ORB


ORB

client

client client

client

server

0 - 1300

9786 - 21340

Banded connections:Invocation priority determines connection to use


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• Protocol configuration– It can be done at the client or

server side of the ORB– Available protocols are exposed

to clients in IORs when the configuration is set from the server side


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RTOS A

Client

ORB A ORB B

Skeleton

RTOS B

Servant

Stub

TCP/IPATM OtherATMTCP/IP

Object Reference

Invocation

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RTOS A

Client

ORB A ORB B

Skeleton

RTOS B

Servant

Stub

TCP/IPATM OtherATMTCP/IP

Invocation timeout

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Some Lessons Learnt

• In general, sources of unsatisfactory results are not easy to find.

• Pattern-based development provides good results but... there is no ORB pattern.

• Improving the ORB by experimenting is of great help. Ask “Why...?”. Run lots of tests.


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Some Lessons Learnt

• Performance– Avoid new/delete. Expensive and

leads to memory fragmentation.– Avoid linear searches

• Unmarshalling IORs• DeMux to object implementation

and operation invocation.– Copying of data: From client to ORB

to network. From network to ORB to server.


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Some Lessons Learnt

• Performance.– Buffer resizing strategy.– Threads life-cycle. Keep threads

alive but idle.– Avoid overhead of first invocation.

Early binding.– Compare to raw-socket

application to find ORB overhead.– Measure ORB behavior with

varying data sizes. (must be linear)


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Some Lessons Learnt

• Predictability– Worst time case is hard to find:

several sources of non determinism (application, ORB, OS, network).

– Configure the ORB in a simpler manner to reduce the number of “changing things” (e.g. Use static buffers).

– Being predictable introduces ORB overhead (priority service contexts)


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Some Lessons Learnt

• Footprint– What is too much?– Performance vs. Footprint– Performance vs. Services

provided– Memory left on board by the ORB

for the application– Bound memory usage by the ORB– Size of the ORB library


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Industry Trends

• The embedded industry is not used to object solutions

• Embedded systems have issues not considered in the RT CORBA specification

• There is no embedded CORBA specification

• Let the user configure default behavior of the ORB (e.g. Default multiplexing of connections)

• Preallocation and control of ORB resources


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Industry Trends

• Usage of multiple protocol stacks: adopt the OCI framework

• The ORB architecture must be open to developers: configure ORB in a “plug-in” fashion.

• Tracing execution and debugging tools

• Specialised services for real-time


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The DOTS Project

• Overview• Participants• Objectives• Domain• Elitel-5: an embedded device• Some results


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Overview

• Overview– To establish an open software

model, built upon real-time distributed object technologies and emergent telecontrol standards to allow the optimum exploitation of the interoperation capabilities of devices and systems in the distributed context of an electric power grid.


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Objectives

• Distributed Object Telecontrol Systems & Networks

• IST-1999-10258-DOTS• Real-Time CORBA• Minimum CORBA• IEC-61850 for control systems

in electrical substations


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Objectives

• From the IEC-61850 draft1. The functions of the substation automation system (SAS) and

their communication behaviour shall be described device independent.

2. The functions shall be described as far as necessary only to identify the information to be exchanged.

3. The free allocation of functions to devices shall be supported.4. The functions used today are well known but the standard

shall be open for future requirements.5. The interaction of device independent distributed functions

shall be described by the logical interfaces in between which may be freely allocated to physical interfaces or LANs.

6. The standard shall define generic information to be communicated and the communication behaviour of the functions to provide for planned and future functional extensions of substation automation system.


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The DOTS Project


Domain of application

CORBA-IEDCORBA Gateway

Station Computer

CORBA-RTU

DOTS-010-1

RTORB Non RTORB

LN

LN LN

LN LN

LN

CORBA Gateway

Non CORBA-IED

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The DOTS Project

• The pilot application Introduction RT CORBA Dev. DOTS Project Conclusions

C ontro l Build ing C om m unication R oom

Build ing C R -1

O IT & SC T C om puter

H U B

H U BIED 1

IED 2

Substation C om puter Video C am era

R ing Button

R eal D ig ita l Input S ignals

R eal analog signals

S im ulate D ig ita l Input S ignals

S im ulate Analog S ignalsS im ulate D ig ita l O utput S ignals

R J-45 E thernet

R J-45 E thernet R J-45 E thernet

R J-45 E thernet

R G -59 v ideo cab le

O F

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The DOTS Project

Elite

l 5

RTORB

Real-Time POA

Client Propagated Priority Model

Threadpools

ICa MinRT VisiBrokerOIT

IIO

P

Process

IEC-61850


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The DOTS Project

• Physical devices– OIT: Operator Interface Tool– IED1: Elitel 5 with blocking control– IED2: Elitel 5 with circuit breaker and switchs

• Logical Nodes– IHMI: Human-Machine Interface– XCBR: Circuit Breaker– XSWI: Switch– CILO: Inter-locking

OIT

IED2 IED1

XSWI25

XCBR20CILO0

IHMI0

3' 5'6

52

3

4

1

Supervision of analog and digital signals and digital refresh rate of 100ms


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The DOTS ProjectCaso 1: operación inhibida º

OIT. IHMI0 IED2. XCBR20 IED1. CILO0 IED2. XSWI25

t1 XCBR.set_ctlVal t2 CILO.get_stVal t3 XSWI.get_stVal t4 openedt5 disabledt6 rejected

Tramas Ethernet - GIOP (tiempos en microsegundos)us 1 2 3 4 5 6 7 8 9 10 media máx.t1 20.335.662 45.553.513 52.144.590 58.703.645 64.313.420 74.245.842 79.532.090 95.386.618 97.130.014 106.980.377t2 20.406.110 45.614.671 52.203.864 58.768.336 64.374.433 74.314.190 79.594.563 95.449.168 97.190.656 107.041.147t3 20.473.052 45.682.335 52.271.569 58.832.201 64.442.697 74.383.529 79.666.425 95.518.615 97.262.690 107.110.436t4 20.610.142 45.832.117 52.416.208 58.968.215 64.582.785 74.523.270 79.804.676 95.657.546 97.402.515 107.250.338t5 20.635.061 45.864.838 52.443.386 58.990.098 64.604.270 74.544.635 79.826.270 95.679.531 97.424.028 107.272.837t6 20.659.827 45.888.113 52.467.953 59.012.211 64.626.445 74.566.733 79.852.838 95.701.697 97.446.218 107.295.188t1-t2 70.448 61.158 59.274 64.691 61.013 68.348 62.473 62.550 60.642 60.770 63.137 70.448t2-t3 66.942 67.664 67.705 63.865 68.264 69.339 71.862 69.447 72.034 69.289 68.641 72.034t3-t4 137.090 149.782 144.639 136.014 140.088 139.741 138.251 138.931 139.825 139.902 140.426 149.782t4-t5 24.919 32.721 27.178 21.883 21.485 21.365 21.594 21.985 21.513 22.499 23.714 32.721t5-t6 24.766 23.275 24.567 22.113 22.175 22.098 26.568 22.166 22.190 22.351 23.227 26.568t1-t6 324.165 334.600 323.363 308.566 313.025 320.891 320.748 315.079 316.204 314.811 319.145 334.600


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The DOTS Project

Caso 2: operación permitida

OIT. IHMI0 IED2. XCBR20 IED1. CILO0 IED2. XSWI25

t1 XCBR.set_ctlVal t2 CILO.get_stVal t3 XSWI.get_stVal t4 closedt5 enabled

IED2. SD1close

t6 accepted

us 1 2 3 4 5 6 7 8 9 10 media máx.t1 2.499.720 5.365.568 7.835.573 9.296.164 15.425.039 19.646.169 21.981.022 24.083.936 28.529.510 32.992.953t2 2.563.527 5.429.650 7.900.292 9.361.910 15.487.889 19.709.996 22.046.448 24.149.677 28.593.594 33.060.292t3 2.631.717 5.493.665 7.966.715 9.427.648 15.565.181 19.784.617 22.112.679 24.218.979 28.661.929 33.125.986t4 2.767.646 5.630.963 8.104.121 9.570.560 15.704.305 19.924.838 22.255.135 24.362.593 28.803.099 33.269.912t5 2.789.230 5.652.693 8.128.383 9.596.547 15.726.077 19.956.273 22.276.619 24.387.501 28.824.590 33.295.873t6 2.892.260 5.762.258 8.232.135 9.698.891 15.829.857 20.064.049 22.386.585 24.492.481 28.930.021 33.405.228t1-t2 63.807 64.082 64.719 65.746 62.850 63.827 65.426 65.741 64.084 67.339 64.762 67.339t2-t3 68.190 64.015 66.423 65.738 77.292 74.621 66.231 69.302 68.335 65.694 68.584 77.292t3-t4 135.929 137.298 137.406 142.912 139.124 140.221 142.456 143.614 141.170 143.926 140.406 143.926t4-t5 21.584 21.730 24.262 25.987 21.772 31.435 21.484 24.908 21.491 25.961 24.061 31.435t5-t6 103.030 109.565 103.752 102.344 103.780 107.776 109.966 104.980 105.431 109.355 105.998 109.966t1-t6 392.540 396.690 396.562 402.727 404.818 417.880 405.563 408.545 400.511 412.275 403.811 417.880


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The DOTS Project

• Some results– DOTS is the first implementation

of the IEC-61850 standard– Contribution to the adoption of

the IEC-61850 standard• General Model Definition• Specific Communication Service

Mapping-Mapping to CORBA

– Embedded IEC-61850 SW for IED and RTU over the SCILabs’ ICa ORB


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The DOTS Project

• Some results of SCILabs Introduction RT CORBA Dev. DOTS Project Conclusions

Version: Release ICA ORB Performance TestServer: LunesClient: BelcebubNumber of Calls: 1000

ORBSequence of Octets

Sequence of Shorts

Sequence of Octets

Sequence of Shorts

Sequence of Octets

Sequence of Shorts

Sequence of Octets

Sequence of Shorts

ICA (SCILabs) 1132 1132 1342 1352 5568 5569 10275 10276VISIBROKER (Borland) 1352 1262 1492 1482 5698 5669 10375 10386TAO (Washington University) 1600 1600 1600 1600 6400 6400 11600 11240ORBIX/E (Iona) 1052 1042 1272 1261 5549 5548 10296 10495EORB (Vertel) 861 862 1071 1082 5229 5728 10797 10495

144

DataSize in bytes

OneWay TwoWay4816

OneWay TwoWay

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Conclusions

• Real-Time CORBA is beginning to be used by the RT/embedded systems community

• There is need for an embedded CORBA specification

• Battle to improve performance, footprint and ORB determinism


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