Lecture #4: Modeling Embedded SystemsReading List for This LectureHow to Design Embedded Systems? (Wescon 1975)Ad Hoc Design Techniques and Heuristic Approaches for Embedded SystemsLaws on Existential PessimismProminent Examples of Embedded Systems Failures: Space ShuttleProminent Examples of Embedded Systems Failures: Patriot MissileSystematic Design of Embedded SystemsTools and Models for Systematic DesignAbstractions and ModelsGood ModelsSeparate Behavior from ArchitectureElements of a Model of a Computation System: LanguageSimulation and SynthesisModels Useful In Validating DesignsHeterogeneous SystemsModeling Embedded SystemsGeneric Embedded SystemsImportance of Time in Embedded Systems: Reactive OperationReactive Operation (contd.)What does real time mean?Real-time TasksDesirable FeaturesExample: Characterizing Real-time Performance of an OSTiming ConstraintsMany Notions of TimeTiming Constraints in a DSP SystemsAchievable Latency and Sample RateLatency vs. Throughput Which is “Harder” Real-time?More General Timing ConstraintsMaximum Timing ConstraintsObservationMinimum Timing ConstraintsMore Complex Timing ConstraintsPopular Computation Models for Embedded SystemsHow do the models differ?Example: Modeling DSP SystemsDigression: Graphs as an Abstract Syntax for ModelsFinite State MachinesFSM ExamplesMore Complex FSMProtocol Controller FSMFSM ExampleNon-Deterministic FSMMealy-Moore FSMsRetrigerrable One-shot TimerProblems with Conventional FSMScalabilitySlide 49ConcurrencySlide 51Mealy-Moore SolutionConcurrent State Model SolutionOrthogonal ComponentsApproach 1: Enumerate AllApproach 2Harel’s StateCharts: Extension of Conventional FSMsFeatures of StateChartsBasic Harel SyntaxState DecompositionStateChart OR-decompositionStateChart AND-decompositionStateCharts SyntaxTransitionsStateCharts Actions and EventsOrder of Nested ActionsHistoryConditional TransitionsAnother Example of the Power of StateChart FormalismExample: Jolt Cola MachineThe Combined State Machine in StateChart FormalismExample: Coin Receptacle FSMSubstate: Issuing CanClass Button FSMConcurrent StatechartsSlide 76Slide 77Explicit SynchronizationExample Concurrent FSMCommunication in Concurrent FSMsPropagations and BroadcastsGraphical Hierarchical FSM LanguagesRaphsody, StateMate etc. by i-LogixCo-design Finite State Machines (CFSMs)Network of CFSMsCommunication PrimitivesMore on EventsGeneralization to SignalsExample CFSM SpecificationNetwork of CFSMs: Depth-1 BuffersDiscrete EventsSimultaneous Events in the Discrete Event ModelReactive Synchronous ModelsEsterelEsterel ExampleData Flow Based ModelsData Flow NetworkFlow Graph ModelsSemanticsSynchronous Data FlowWhat Latency & Sample Period an a SDFG achieve?SDFG can be Transformed to Affect TL & TSDataflow Process NetworksSynchronous vs. AsynchronousAsynchronous CommunicationsCommunication ModelsModeling Approaches based on Software Design MethodsHow Models Influence an Application Design?Choice of ModelCopyright © 2005EEM202A/CSM213A - Fall 2005Mani SrivastavaUCLA - [email protected]://nesl.ee.ucla.eduLecture #4: Modeling Embedded Systems2Reading List for This Lecture•MANDATORY READING–Edward A. Lee, "Embedded Software," in Advances in Computers (M. Zelkowitz, editor), Vol. 56, Academic Press, London, 2002. http://ptolemy.eecs.berkeley.edu/publications/papers/02/embsoft/–Stephen A. Edwards, “Design Languages for Embedded Systems,” Computer Science Technical Report CUCS-009-03, Columbia University. http://www1.cs.columbia.edu/~sedwards/papers/edwards2003design.pdf–Gerard Berry, “Foundations of Esterel,” Proof, Language and Interaction: Essays in Honour of Robin Milner, 1998.http://citeseer.nj.nec.com/62412.html–Harel, D.; Lachover, H.; Naamad, A.; Pnueli, A.; Politi, M.; Sherman, R.; Shtull-Trauring, A.; Trakhtenbrot, M. STATEMATE: a working environment for the development of complex reactive systems. IEEE Transactions on Software Engineering, vol.16, (no.4), April 1990. p.403-14.http://citeseer.nj.nec.com/harel90statemate.html•RECOMMENDED READING–Johan Eker, Jörn W. Janneck, Edward A. Lee, Jie Liu, Xiaojun Liu, Jozsef Ludvig, Stephen Neuendorffer, Sonia Sachs, Yuhong Xiong, "Taming Heterogeneity---the Ptolemy Approach," Proceedings of the IEEE , v.91, No. 2, January 2003. http://ptolemy.eecs.berkeley.edu/publications/papers/03/TamingHeterogeneity/3How to Design Embedded Systems? (Wescon 1975)•“...deliberately avoid data processing aides such as assemblers, high-level languages, simulated systems, and control panels. These computer-aided design tools generally get in the way of cost-effective design and are more a result of the cultural influence of data processing, rather than a practical need.”•“It’ s my observation that the bulk of real-world control problems require less than 2,000 instructions to implement. For this size program computer aided design does little to improve the design approach and does a lot to separate the design engineer from intimate knowledge of his hardware.”4Ad Hoc Design Techniques and Heuristic Approaches for Embedded Systems•Common approach–Large portions of code in assembly–Programming timers, low-level device drivers, task and interrupt manipulation•Optimized for efficiency, but many disadvantages–Tedious programming–Difficult to understand and maintain–Difficult to verify timing and memory constraints•Major consequence is unpredictability–System may work fine for a period of time but fail under rare but possible conditions5Laws on Existential Pessimism•Murphy’s General Law (by US Air Force aeronautical engineer Cpt. Ed Murphy, 1949)–If something can go wrong, it will go wrong•Murphy’s Constant–Damage to an object is proportional to its value•Naeser’s Law–One can something bomb-proof, not jinx-proof•Troutman Postulates–Any software bug will tend to maximize the damage–The software bug will be discovered six months after the field test•Green’s Law–If a system is designed to be tolerant to a set of faults, there will always exist an idiot so skilled to cause a nontolerated fault.–Corollary: Dummies are always more skilled than measures taken to keep them from harm•Johnson’s First Law–If a system stops working, it will do it as the worst possible time.•Sodd’s Second Law–Sooner or later; the worst possible combination of circumstances will happen.–Corollary: A system must always be designed to resist the worst possible