Post on 19-Dec-2015
1
IST 37652 Hard Real-time CORBA
HRTC
WP2: Hard Real-Time ProtocolsWP2: Hard Real-Time Protocols
Thomas Losert, Miguel Segarra, Karl-Erik Årzén
HRTC 2
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ContentContent
Introduction – Thomas LosertIntroduction – Thomas Losert CORBA & OCI – Miguel SegarraCORBA & OCI – Miguel Segarra Protocol Issues – Thomas LosertProtocol Issues – Thomas Losert
TTPIOP – Thomas LosertTTPIOP – Thomas Losert RTEIOP – Karl-Erik ÅrzénRTEIOP – Karl-Erik Årzén
HRTC 3
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IntroductionIntroduction
Decision on Testbeds is based on D2.1 Decision on Testbeds is based on D2.1 „Analysis of Protocols for Real-Time „Analysis of Protocols for Real-Time Control“Control“
Chosen TTP/C and RT-Ethernet as Chosen TTP/C and RT-Ethernet as Protocols for the TestbedsProtocols for the Testbeds
100% reliability usually is not necessary in 100% reliability usually is not necessary in Control Systems (thus no retransmissions)Control Systems (thus no retransmissions)
HRTC 4
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Main Activities and AchievementsMain Activities and Achievements
D2.2 HRT Protocol SpecificationD2.2 HRT Protocol SpecificationD2.3 HRT ProtocolD2.3 HRT ProtocolExtra Documents:Extra Documents:
TTP Transport DefinitionTTP Transport DefinitionRTE Transport DefinitionRTE Transport Definition
2 Prototype Implementations based on 2 Prototype Implementations based on OCI exploring different variants (e.g., OCI exploring different variants (e.g., connection-less and connection-oriented)connection-less and connection-oriented)
HRTC 5
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Recommendations from Previous Recommendations from Previous Review regarding D2.2Review regarding D2.2
We have implemented the following:We have implemented the following:The selected pluggable framework (OCI) The selected pluggable framework (OCI)
has been moved to the annexhas been moved to the annexA clarification for synchronization has A clarification for synchronization has
been addedbeen addedWe have issued a revised version of the We have issued a revised version of the
document (e.g., added timestamps, document (e.g., added timestamps, (a)periodic/sporadic tasks, next (a)periodic/sporadic tasks, next transmission time)transmission time)
HRTC 7
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ContentsContents
How does CORBA work?How does CORBA work? Specifications vs RealitySpecifications vs Reality Sources of nondeterminismSources of nondeterminism Real-Time CORBA Transport SelectionReal-Time CORBA Transport Selection Transport Plugin FrameworkTransport Plugin Framework
HRTC 9
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How does CORBA work?How does CORBA work?
•Server Side•Client Side
Object Request BrokerIDL
IDL
POA
CLIENT
SERVANT
IDL
HRTC 10
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How does CORBA work?How does CORBA work?
Object Request BrokerIDL
IDL
POA
CLIENT
SERVANT
Client.GetValue(); Servant.GetValue();
HRTC 11
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How does CORBA work?How does CORBA work?
Object Request BrokerIDL
IDL
POA
CLIENT
SERVANT
Object Request BrokerIDL
IDL
POA
CLIENT
SERVANT
GIOP
Servant.GetValue();
Client.GetValue();
HRTC 13
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Specification vs RealitySpecification vs Reality
Real-Time CORBA
Messaging
CORBA
MinimumCORBA
TimeService
But close to the process resources are very limited!
HRTC 14
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Specification vs RealitySpecification 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!
HRTC 16
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Sources of non-determinismSources of non-determinism
Stub
Client threadpriority
Provide predictability by controlling ORB behavior
ORB
connection
ORBInvoke priority
protocol
Skeleton
POA
threadpriority
concurrency
Servant
HRTC 17
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Sources of non-determinismSources of non-determinism
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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HRTC
Real-Time CORBA Transport SelectionReal-Time CORBA Transport Selection
HRTC 19
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Real-Time CORBA Transport Real-Time CORBA Transport SelectionSelection
ESIOPIIOP
(GIOP/TCP)
ORB
ESIOP
RT_CORBA::ORB
???Others
CORBA::Current
Servant
RT_CORBA::Threadpool
SchedulingService
Client
RT_CORBA::Current
Server
RT_CORBA::Priority
RT_CORBA::PriorityMapping
POA RT POA
•A real-time CORBA broker
HRTC 20
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Real-Time CORBA Transport Real-Time CORBA Transport SelectionSelection
RTOS A
Client
ORB A ORB B
Skeleton
RTOS B
Servant
Stub
TCP/IPTTP OtherTTPTCP/IP
Object Reference
Invocation
HRTC 22
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Transport Plugin FrameworkTransport Plugin Framework
Pluggable transportprotocol
Pluggable messagesupport
Pluggable protocol framework
Acceptor
Connector
POA
threads
ORB
Service handler
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HRTC
OCI:Open Communications
Interface
OCI:Open Communications
Interface
HRTC 24
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Open Communications InterfaceOpen Communications Interface
It is an interface (abstract) for a transport plugin It is an interface (abstract) for a transport plugin frameworkframework It supports connection-oriented, reliable “byte-stream” It supports connection-oriented, reliable “byte-stream”
transports. That is,transports. That is, transports which allow the transports which allow the transmission of a continuous stream of bytestransmission of a continuous stream of bytes (octets) (octets) fromfrom the sender to the receiver.the sender to the receiver.
Non-reliable or non-connection-oriented protocols can Non-reliable or non-connection-oriented protocols can also be used if the transportalso be used if the transport plug-in itself takes care of plug-in itself takes care of reliability and connection management.reliability and connection management.
HRTC 25
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Open Communications InterfaceOpen Communications Interface
ORB
Conn. Fact. Reg. Acc. Fact. Reg.
CLIENT SIDE SERVER SIDE
Conn. Fact. Acc. Fact.AcceptorConnector Transport
TCP/IPConn. Fact.
TCP/IP Acc. Fact.
TCP/IP Acceptor
TCP/IP Connector
TCP/IP Transport
1 1n n
creates
ABSTRACT
IMPLEMENTATION
HRTC 26
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Open Communications InterfaceOpen Communications Interface
OCI
OCI_TCPIP OCI+_RTEOCI+_TTP
GIOP GIOP GIOP
IIOP TTPIOP RTEIOP
HRTC 27
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Open Communications InterfaceOpen Communications Interface
Hardware and software usedHardware and software used Sun UltraSparcSun UltraSparc Power PC for TTP nodesPower PC for TTP nodes Power PC for VME boardsPower PC for VME boards Axis developer boardAxis developer board
Operating systemsOperating systems Sun Solaris 8.0Sun Solaris 8.0 RTAI LinuxRTAI Linux
HRTC 28
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Open Communications InterfaceOpen Communications Interface
We did not foresee to make a lot of We did not foresee to make a lot of modifications to the ORB core but at the modifications to the ORB core but at the end we needed to make modifications in end we needed to make modifications in order to have pure oneway requests and order to have pure oneway requests and to provide special transport handles for to provide special transport handles for RTEthernetRTEthernet
HRTC 30
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General IssuesGeneral Issues
A Distributed Control System must be A Distributed Control System must be aware of the Progression of Timeaware of the Progression of Time
The ORB must be aware of the The ORB must be aware of the Progression of TimeProgression of Time
HRTC 31
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Adding Time AwarenessAdding Time Awareness
Proposed Extension of the Transport: Proposed Extension of the Transport: protocol_timeprotocol_time, , next_transmission_timenext_transmission_time, , delivery_timedelivery_time, and , and precisionprecision
Additional Interfaces in Additional Interfaces in RTCORBARTCORBA-module allow -module allow the Application to Read these Values via the the Application to Read these Values via the RTObject which is an additional interface we RTObject which is an additional interface we have implementedhave implemented
Time-Format should be Simple: Chosen Time Time-Format should be Simple: Chosen Time Format from Smart Transducers Interface Format from Smart Transducers Interface Specification (formal/2003-01-01)Specification (formal/2003-01-01)
HRTC 32
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DeadlinesDeadlines
In RTCORBA just Timeouts are supportedIn RTCORBA just Timeouts are supported(when set at client side)(when set at client side)
Defined policies in the ORB but not Defined policies in the ORB but not implemented in the testbedsimplemented in the testbeds
HRTC 33
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Changes/ExtensionsChanges/Extensions
An RTORB contains a policy that decides An RTORB contains a policy that decides between 100 ns and 60 nsbetween 100 ns and 60 ns
Timestamping (not implemented)Timestamping (not implemented)Proposed extension of IDL allows Proposed extension of IDL allows
classification of tasks: periodic (RT), classification of tasks: periodic (RT), sporadic (RT), and aperiodic (no RT)sporadic (RT), and aperiodic (no RT)
HRTC 34
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IST 37652 / Hard Real-time CORBA
State vs. Event ValuesState vs. Event Values
Characteristic State Observation
Event Observation
Value Full Value Value Difference
Frequency Periodic Sporadic
Loss of Observ. Period lost Loss of synch.
Semantics At-least-once Exactly-once
Error Detection At receiver At sender only
HRTC 36
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ComposabilityComposabilityWe call an architecture We call an architecture composablecomposable with respect to a with respect to a
specified property, if the system integration will not specified property, if the system integration will not invalidate this property provided it has been established at invalidate this property provided it has been established at the subsystem level, e.g.:the subsystem level, e.g.: TimelinessTimeliness TestabilityTestability
System properties should follow from subsystem System properties should follow from subsystem properties.properties.Otherwise the system integrator is left with the challenging Otherwise the system integrator is left with the challenging task to find out why the system does not work, although task to find out why the system does not work, although all subsystems work according to their specifications.all subsystems work according to their specifications.
HRTC 37
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TDMA Media AccessTDMA Media Access
assigned tonode 0
assigned tonode 1
assigned tonode 2
assigned tonode 3
12:00 3:00 5:00 9:00 12:00
assigned tonode 3
assigned tonode 0
slot 0 slot 1 slot 2 slot 3 slot 0slot 3
TDMA round nTDMA round (n-1) TDMA round (n+1)
Real Time
TT communication systemTT communication systemPeriodic transmission of state messagesPeriodic transmission of state messagesTwo redundant channels with TDMATwo redundant channels with TDMA
Sending slotsSending slots TDMA roundsTDMA rounds
HRTC 38
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Flow of State and Event Flow of State and Event Information in TTPIOPInformation in TTPIOP
OCI
ORB
TTP
GIOP
GIOP
Servant
RT Data
OCI
ORB
TTP
GIOP
GIOP
Client
RT Data
Node n-1 Node n Node n+1
CORBA RT Data
Event Information
State Information
IST 37652 Hard Real-time CORBA
HRTC
RTEIOPRTEIOP
Real-Time Communication over Switched Ethernet ThrottleNet: The link layer in the RT Ethernet approach
HRTC 40
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• Isolated collision domains • Full duplex communication• Inexpensive hardware (COTS) and high performance• Traffic control (throttling) guarantees end-to-end latency• Buffer delay causes jitter
Switched EthernetSwitched Ethernet
Switch
HRTC 41
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Periodic Real-Time ChannelPeriodic Real-Time Channel
One-way communication channelOne-way communication channel between sender and receiver between sender and receiver
Parameters:Parameters: Frequency (maximum send rate)Frequency (maximum send rate) Maximum transmit time (maximum message Maximum transmit time (maximum message
size)size) Maximum allowed latencyMaximum allowed latency
Schedulability analysis decides if latency Schedulability analysis decides if latency constraint holds constraint holds
HRTC 42
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Non Real-Time TrafficNon Real-Time Traffic
Bandwidth is allocated to non-real time Bandwidth is allocated to non-real time traffic traffic
TCP, UDP, ….TCP, UDP, ….
HRTC 43
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ThrottlingThrottling
Traffic control through bufferingTraffic control through buffering Ensure that sending nodes do not Ensure that sending nodes do not
violate their periodicity violate their periodicity Bandwidth limitationBandwidth limitation Applies to real-time traffic and non real-Applies to real-time traffic and non real-
time traffic time traffic
HRTC 44
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Schedulability AnalysisSchedulability Analysis Worst-case basedWorst-case based Calculate the latencies for the worst-caseCalculate the latencies for the worst-case
buffering scenario buffering scenario Take the buffer overflow into account Take the buffer overflow into account May result in considerable jitterMay result in considerable jitter Implemented by a special node Implemented by a special node
(the “GlobeThrottle”) (the “GlobeThrottle”) Dynamic admission of new channelsDynamic admission of new channels
HRTC 45
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GlobeThrottleGlobeThrottleGlobeThrottle:• contains the global traffic information• schedules the RT traffic requests• updates the nodes when the schedule is changed• router for non-RT traffic• gateway to Internet• converts incoming broadcasts
to scheduled unicasts
GlobeThrottle
HRTC 46
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RT-LayerRT-Layer
RT layer:RT layer: Traffic control for worst-Traffic control for worst-
case scheduling case scheduling Distinguish RT and non-Distinguish RT and non-
RT traffic (RT header) RT traffic (RT header) FragmentationFragmentation
Non RT trafficNon RT traffic RT traffic (may improve RT traffic (may improve
schedulability)schedulability)
HRTC 47
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Related WorkRelated Work
K.G Shin et al (U of Michigan)K.G Shin et al (U of Michigan) Throttled shared EthernetThrottled shared Ethernet Statistical latency boundsStatistical latency bounds
RTnetRTnet Time-triggered Real-Time EthernetTime-triggered Real-Time Ethernet RTAIRTAI Univ of HannoverUniv of Hannover
HRTC 49
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ThrottleNet and CORBAThrottleNet and CORBA ThrottleNet as the data link layerThrottleNet as the data link layer Real-time CORBA requests on the same Real-time CORBA requests on the same
network as ordinary CORBA requests network as ordinary CORBA requests
HRTC 50
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Ordinary CORBA trafficOrdinary CORBA traffic
IIOP messages tunneled over ThrottleNetIIOP messages tunneled over ThrottleNet Fragmented and buffered to not disturb Fragmented and buffered to not disturb
the real-time traffic the real-time traffic ThrottleNet transparent to IIOPThrottleNet transparent to IIOP Buffering the only effect on IIOPBuffering the only effect on IIOP
HRTC 51
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Real-Time TrafficReal-Time Traffic
GIOP requests from client to server GIOP requests from client to server mapped to mapped to ThrottleNet real-time channels ThrottleNet real-time channels
True one-way requestsTrue one-way requests Support for this added to the ICa ORBSupport for this added to the ICa ORB
GIOP messages tunneled over GIOP messages tunneled over ThrottleNet ThrottleNet
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Real-Time TrafficReal-Time Traffic Explicit connection bindings Explicit connection bindings
-- -- validate_connectionvalidate_connection avoid binding related overheadavoid binding related overhead the communication between the client and the communication between the client and
server in connection with the binding is from a server in connection with the binding is from a scheduling point of view be considered as scheduling point of view be considered as being part of the real-time channel being part of the real-time channel communicationcommunication
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ThrottleNet CORBAThrottleNet CORBA
OCI with two parallel OCI with two parallel transport plug-ins transport plug-ins
The application The application decides which decides which transport to use transport to use
EthernetInterface
IP
TCP
IIOP
RT-ORB
RTE
OCI+
CORBA client &server application code
ThrottleNet
RT
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ThrottleNet R-T ClientThrottleNet R-T Client
1.1. Register the communication channel with Register the communication channel with the GlobeThrottle server.the GlobeThrottle server.
2.2. If schedulability test in GlobeThrottle If schedulability test in GlobeThrottle returns OKreturns OK
Setup explicit connectionSetup explicit connection Communicate over the connectionCommunicate over the connection
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GlobeThrottleGlobeThrottle
Could be implemented in different waysCould be implemented in different ways1.1. As an ordinary CORBA object residing in As an ordinary CORBA object residing in
one the nodes.one the nodes.• Communication using IIOPCommunication using IIOP
2.2. As a new CORBA “real-time scheduling” As a new CORBA “real-time scheduling” serviceservice
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Main CharacteristicsMain Characteristics
Close in spirit to ordinary CORBAClose in spirit to ordinary CORBA UnicastUnicast Invocation-oriented event-triggered communicationInvocation-oriented event-triggered communication
RT traffic and CORBA IIOP traffic coexist RT traffic and CORBA IIOP traffic coexist on the network on the network
One-way communicationOne-way communication Hard upper bounds on latency, but considerableHard upper bounds on latency, but considerable
jitter jitter Open Issues:Open Issues:
Is the GIOP message format efficient enough?Is the GIOP message format efficient enough?
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Possible Future ExtensionPossible Future Extension
Global ClockGlobal Clock Improves schedulability and reduces jitterImproves schedulability and reduces jitter Compare RTnetCompare RTnet
Schedulability analysis for two-waySchedulability analysis for two-way invocations invocations
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OutlookOutlook
Moving ORB from Usermode to Moving ORB from Usermode to Kernelmode is outside the scope of this Kernelmode is outside the scope of this projectproject
Tool for offline-scheduling of IDL (for Tool for offline-scheduling of IDL (for TTPIOP)TTPIOP)
Clock Synchronisation (for RTEIOP)Clock Synchronisation (for RTEIOP)Running the ORB in RTAI context or Running the ORB in RTAI context or
running the ORB in user context (e.g., with running the ORB in user context (e.g., with lxrt)lxrt)