Real-Time Systems. Design Principles for Distributed Embedded Applications. Herman Kopetz. Second Edition (811374), страница 97
Текст из файла (страница 97)
Kopetz, Real-Time Systems: Design Principles for Distributed Embedded Applications,Real-Time Systems Series, DOI 10.1007/978-1-4419-8237-7,# Springer Science+Business Media, LLC 2011341342AbbreviationsTDMATMRTTTTATTEthernetTTPUIDUTCWCAOWCCOMWCETWSNTime-Division Multiple AccessTriple-Modular RedundancyTime TriggeredTime-Triggered ArchitectureTime-Triggered EthernetTime-Triggered ProtocolUnique IdentifierUniversal Time CoordinatedWorst-Case Administrative OverheadWorst-Case Communication DelayWorst-Case Execution TimeWireless Sensor NetworkGlossaryNote: All terms that are defined in this glossary are put in italics. At the end of eachentry the section of the book that introduces or discusses the term is mentioned inthe parenthesis.Absolute TimestampAccuracy IntervalAccuracy of a ClockActionAction DelayActuatorAdvanced EncryptionStandard (AES)Audio VideoBus (AVB)Agreed DataAn absolute timestamp of an event e is the timestamp ofthis event that is generated by the reference clock(3.1.2).The maximum permitted time interval between the pointof observation of a real-time entity and the point of useof the corresponding real-time image (5.4).The accuracy of a clock denotes the maximum offset ofa given clock from the external time reference during thetime interval of interest (3.1.3).An action is the execution of a program or a communication protocol (1.3.1).The action delay is the maximum time interval betweenthe start of sending a message and the instant when thismessage becomes permanent at the receiver (5.5.1).A transducer that accepts data and trigger informationfrom a gateway component and realizes the intendedphysical effect in the controlled object (9.5).An international standard for the encryption of data(6.2.2).The IEEE 802.1 audio/video bridging (AVB) task forcedevelops a set of protocols based on the Ethernet standard that meets the requirements of multimedia systems(7.4.4).An agreed data element is a measured data element thathas been checked for plausibility and related to othermeasured data elements, e.g., by the use of model of thecontrolled object.
An agreed data element has beenjudged to be a correct image of the corresponding realtime entity (➔ raw data, measured data) (9.6).343344Agreement ProtocolAlarm MonitoringAlarm ShowerAnalytic RationalSubsystemAnytime AlgorithmAperiodic TaskApplicationProgrammingInterface (API)A Priori KnowledgeARINC 629 ProtocolAssumption CoverageAtomic ActionAtomic Data StructureAvailabilityGlossaryAn agreement protocol is a protocol that is executedamong a set of components of a distributed system tocome to a common (agreed) view about the state of theworld, both in the discrete value domain and in thesparse time domain (9.6).Alarm monitoring refers to the continuous observationof the RT entities to detect an abnormal behavior of thecontrolled object (1.2.1).An alarm shower is a correlated set of alarms that iscaused by a single primary event (1.2.1).A conscious human problem-solving subsystem thatoperates according to the laws of causality and logic(2.1.1).An anytime algorithms consist of a root segment thatcalculates a first approximation of the result of sufficientquality and a periodic segment that improves the qualityof the previously calculated result.
The periodic segment is executed repeatedly until the deadline is reached(10.2.3).An aperiodic task is a task where neither the task requesttimes nor the minimum time interval between successiverequests for activation are known (➔ periodic task, ➔sporadic task) (10.1.2).The interface between an application program and theoperating system within a component (9.1.4).Knowledge about the future behavior of a system that isavailable ahead of time (1.5.5).A medium access protocol that controls access to a singlecommunication channel by a set of components. It isbased on a set of carefully selected time-outs (7.4.2).Assumption coverage is the probability that assumptionsthat are made in the model building process hold inreality. The assumption coverage limits the probabilitythat conclusions derived from a perfect model will bevalid in the real world (1.5.3).An atomic action is an action that has the all-or-nothingproperty.
It either completes and delivers the intended resultor does not have any effect on its environment (4.2.3).An atomic data structure is a data structure that has to beinterpreted as a whole (4.3).Availability is a measure of the correct service deliveryregarding the alternation of correct and incorrect service, measured by the fraction of time that the system isready to provide the service (1.4.4).GlossaryBabbling IdiotBack-Pressure FlowControlBasic MessageTransportService (BMTS)Benign FailureBest EffortBit-length ofa ChannelBus GuardianByzantine ErrorCausal OrderCausalityClockClusterCognitive Complexity345A component of a distributed computer system thatsends messages outside the specified time interval iscalled a babbling idiot (4.7.1).In back-pressure flow control the receiver of a sequenceof messages exerts back pressure on the sender so thatthe sender will not outpace the receiver (7.3.2).The basic message transport service transports a message from a sending component to one or more receiving components (7.2.1).A failure is benign if the worst-case failure costs are ofthe same order of magnitude as the loss of the normalutility of the system (6.1.3).A real-time system is a best-effort system if it is notpossible to establish the temporal properties by analytical methods, even if the load- and fault hypothesis holds(➔ guaranteed timeliness) (1.5.3).The bit length of a channel denotes the number of bitsthat can traverse the channel within one propagationdelay (7.2.2).The independent hardware unit of a TTP controller thatensures fail silence in the temporal domain (7.5.1).A Byzantine error occurs if a set of receiversobserves different (conflicting) values of a RT entity.Some or all of these values are incorrect (synonym:malicious error, two-faced error, inconsistent error)(3.4.1).A causal order among a set of events is an order thatreflects the cause-effect relationships between the events(3.1.1).The causality relationship between a cause C and anevent E is defined as follows: If C happens, then E isalways produced by it (2.1.1).A clock is a device for time measurement that contains acounter and a physical oscillation mechanism that periodically generates an event, the ➔ tick or ➔ microtick ofthe clock, to increase the counter (3.1.2).A cluster is a subsystem of a real-time system.
Examplesof clusters are the real-time computer system, the operator, or the controlled object (1.1).The elapsed time needed to ➔ understand a model bya given observer is a measure for the cognitive effortand thus for the cognitive complexity of a model relativeto the observer. We assume that the given observeris representative for the intended user group of themodel.346Complex Task (C-task)ComponentComposabilityComputational ClusterConceptConceptual LandscapeConcrete WorldInterfaceConcurrency ControlField (CCF)Consistent FailureContact BounceControl AreaNetwork (CAN)Controlled ObjectConvergence FunctionDeadlineGlossaryA complex task (C-task) is a task that contains a blocking synchronization statement (e.g., a semaphore operation wait) within the task body (9.2.3).A component is a hardware-software unit, i.e., a selfcontained computer including system- and applicationsoftware that performs a well-defined function within adistributed computer system (4.1.1).An architecture is composable regarding a specifiedproperty if the system integration will not invalidatethis property, provided it has been established at thesubsystem level (4.7.1).A subsystem of a real-time system that consists of aset of components interconnected by a real-time communication network (1.1).A concept is a category that is augmented by aset of beliefs about its relations to other categories.The set of beliefs relates a new concept to alreadyexisting concepts and provides for an implicit theory(2.1.2).The conceptual landscape refers to the personal knowledge base that has been built up and maintained byan individual in the experiential and rational subsystemof the mind (2.2).The concrete world interface is the physical I/O interface between an interface component and an externaldevice or another external component (4.5).The concurrency control field (CCF) is a single-worddata field that is used in the NBW protocol (9.4.2).A consistent failure occurs if all users see the sameerroneous result in a multi-user system (6.1.3).The random oscillation of a mechanical contact immediately after closing (9.5.2).The control area network (CAN) is a low-cost eventtriggered communication network that is based onthe carrier-sense multiple-access collision-avoidancetechnology (7.3.2).The controlled object is the industrial plant, the process,or the device that is to be controlled by the real-timecomputer system (1.1).The convergence function denotes the maximum offsetof the local representations of the global time within anensemble of clocks (3.4).A deadline is the instant when a result should/must beproduced (➔ soft deadline, firm deadline, and harddeadline) (1.1).GlossaryDeadline IntervalDeterminismDriftDrift OffsetDurationDynamic SchedulerEarliest-Deadline-First(EDF) AlgorithmElectro-MagneticInterference (EMI)Electronic ProductCode (EPC)Embedded SystemEmergenceEnd-to-End ProtocolEnvironment ofa ComputationalClusterErrorError-ContainmentCoverage347The deadline interval is the interval between the taskrequest time and the deadline (10.1).A physical system behaves deterministically if given aninitial state at instant t and a set of future timed inputs,then the future states and the values and times of futureoutputs are entailed.
In a deterministic distributed computer system, we must assume that all events, e.g., theobservation of the initial state at instant t and the timedinputs, are sparse events on a sparse global time base(5.6.1).The drift of a physical clock k between microtick i andmicrotick i+1 is the frequency ratio between this clock kand the reference clock at the time of microtick i. (3.1.2).The drift offset denotes the maximum deviation betweenany two good clocks if they are free running during theresynchronization interval (3.1.4).A duration is a section of the timeline (3.1.1).A dynamic scheduler is a scheduler that decides at runtime after the occurrence of a significant event whichtask is to be executed next (10.4).An optimal dynamic preemptive scheduling algorithmfor scheduling a set of independent tasks (10.4.1).The disturbance of an electronic system by electromagnetic radiation (11.3.4).A code designed by the RFID community that can be usedto uniquely identify every product on the globe (13.4.2).A real-time computer that is embedded in a well specified larger system, consisting in addition to the embedded computer of a mechanical subsystem and, often, aman-machine interface (➔ intelligent product) (1.6.1).We speak of emergence when the interactions of subsystems give rise to unique global properties at thesystem level that are not present at the level of thesubsystems.An end-to-end protocol is a protocol between the users(machines or humans) residing at the end points of acommunication channel (1.7).The environment of a given computational cluster is theset of all clusters that interact with this cluster, eitherdirectly or indirectly (1.1).An error is that part of the state of a system that deviatesfrom the intended specification (6.1.2).Probability that an error that occurs in an errorcontainment region is detected at one of the interfacesof this region (6.4.2).348Error-ContainmentRegionEventEvent MessageEvent-triggered(ET) ObservationEvent-Triggered(ET) SystemExact VotingExecution TimeExplicit Flow ControlExternal ClockSynchronizationFail-OperationalSystemFail-Safe SystemFail-SilenceFailureGlossaryA subsystem of a computer system that is encapsulatedby error-detection interfaces such that the there is a highprobability (the ➔ error containment coverage) that theconsequences of an error that occurs within this subsystem will not propagate outside this subsystem withoutbeing detected (6.4.2).An event is a happening at a cut of the time-line.
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