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Using Vergil event time and the previous event time, resulting in the plot that is shown in the figure. The Previous actor is a zero-delay actor, meaning that it produces an output with the same time stamp as the input (except on the first firing, where in this case it produces no output). Thus, when the PoissonClock actor produces an output, there will be two simultaneous events, one at the input to the plus port of the FIGURE 2.51. Model time vs. real time (wall clock time). FIGURE 2.52. Histogram of interarrival times, illustrating handling of simultaneous events. 80 Ptolemy <strong>II</strong>
Using Vergil AddSubtract actor, and one at the input of the Previous actor. Should the director fire the AddSubtract actor or the Previous actor? Either seems OK if it is to respect chronological order, but it seems intuitive that the Previous actor should be fired first. It is helpful to know how the AddSubtract actor works. When it fires, it adds at most one token from each channel of the plus port, and subtracts at most one token from each channel of the minus port. If the AddSubtract actor fires before the Previous actor, then the only available token will be the one on the plus port, and the expected subtraction will not occur. Intuitively, we would expect the director to invoke the Previous actor before the AddSubtract actor so that the subtraction occurs. How does the director deliver on the intuition that the Previous actor should be fired first? Before executing the model, the DE director constructs a topological sort of the model. A topological sort is simply a list of the actors in data-precedence order. For the model in figure 2.52, there is only one allowable topological sort: PoissonClock, CurrentTime, Previous, AddSubtract, HistogramPlotter In this list, AddSubtract is after Previous. So the when they have simultaneous events, the DE director fires Previous first. Thus, the DE director, by analyzing the structure of the model, usually delivers the intuitive behavior, where actors that produce data are fired before actors that consume their results, even in the presence of simultaneous events. There remains one key subtlety. If the model has a directed loop, then a topological sort is not possible. In the DE domain, every feedback loop is required to have at least one actor in it that introduces a time delay, such as the TimedDelay actor, which can be found in the DomainSpecific library under DiscreteEvent (this library is shown on the left in figure 2.53). Consider for example the model shown in figure 2.53. That model has a Clock actor, which is set to produce events every 1.0 time units. Those events trigger the Ramp actor, which produces outputs that start at 0 and increase by 1 on each firing. In this model, the output of the Ramp goes into an AddSubtract actor, which subtracts from the Ramp output its own prior output delayed by one time unit. The result is shown in the plot in the figure. Occasionally, you will need to put a TimedDelay actor in a feedback loop with a delay of 0.0. This is particularly true if you are building complex models that mix domains, and there is a delay inside a composite actor that the DE director cannot recognize as a delay. The TimedDelay actor with a delay of 0.0 can be thought of as a way to let the director know that there is a time delay in the preceding actor, without specifying the amount of the time delay. 2.9.4 Wireless and Sensor Network Systems The wireless domain builds on the discrete event domain to support modeling of wireless and sensor network systems. In the wireless domain, channel models mediate communication between actors, and the visual syntax does not require wiring between components. See [10] and [11] for details. 2.9.5 Continuous-Time Systems The continuous-time domain (CT) is another relatively mature domain with semantics considerably different from either DE or SDF. In CT, the signals sent along connections between actors are usually continuous-time signals. A CT example is described above in section 2.2.3. The CT domain can also handle discrete events. These events are usually related to a continuoustime signal, for example representing a zero-crossing of the continuous-time signal. The CT director is quite sophisticated in its handling of such mixed signal systems. Heterogeneous Concurrent Modeling and Design 81
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PTOLEMY II HETEROGENEOUS CONCURRENT
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VOLUME 1 INTRODUCTION TO PTOLEMY II
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Volume 1 Contents Introduction to P
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2.10.3. Constructing Modal Models 8
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7. MoML 191 7.1. Introduction 191 7
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1 Introduction Author: Edward A. Le
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Introduction heterochronous dataflo
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Introduction A major emphasis in Pt
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Introduction determine when actors
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Introduction provides levels of vis
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Introduction is a guard, and the se
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Introduction well. All of these are
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Introduction clients to update thei
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Introduction will be supplied with
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Introduction 1.3.12 Synchronous Dat
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Introduction FIGURE 1.10. Refinemen
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Introduction occlusions due to terr
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Introduction tion. The overall arch
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Introduction kernel.attributes This
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Page 41 and 42: Introduction Actor interfaces are k
Page 43 and 44: Heterogeneous Concurrent Modeling a
Page 45 and 46: Introduction actor actor.gui data.e
Page 47 and 48: Introduction cient, scalable, and u
Page 49 and 50: Introduction 1.5.8 Future Capabilit
Page 51 and 52: Introduction Appendix A: UML — Un
Page 53 and 54: Introduction grams, the only constr
Page 55 and 56: 2 Using Vergil Authors: Edward A. L
Page 57 and 58: Using Vergil 2.2.2 Executing a Pre-
Page 59 and 60: Using Vergil The Lorenz attractor m
Page 61 and 62: Using Vergil The Continuous-Time (C
Page 63 and 64: Using Vergil box in figure 2.11. En
Page 65 and 66: Using Vergil Don’t panic! Excepti
Page 67 and 68: Using Vergil tions are a normal par
Page 69 and 70: Using Vergil 2.4 Hierarchy Ptolemy
Page 71 and 72: Using Vergil Then using these ports
Page 73 and 74: Using Vergil the default 0.1 to 0.0
Page 75 and 76: Using Vergil pan window, it is easy
Page 77 and 78: Using Vergil FIGURE 2.33. The pan w
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Page 81 and 82: Using Vergil model, simply copy (or
Page 83 and 84: Using Vergil A key issue is to deci
Page 85 and 86: Using Vergil instances. This proble
Page 87 and 88: Using Vergil quick tour for more de
Page 89: Using Vergil uses the index in the
Page 93 and 94: Using Vergil If you look inside the
Page 95 and 96: Using Vergil If you look inside the
Page 97 and 98: Using Vergil transition (or right c
Page 99 and 100: Using Vergil Once you have created
Page 101 and 102: Using Vergil The grid is turned off
Page 103 and 104: Authors: Edward A. Lee Xiaojun Liu
Page 105 and 106: Expressions classes to create a gen
Page 107 and 108: Expressions The % operation is a mo
Page 109 and 110: Expressions attribute, which includ
Page 111 and 112: Expressions 3.3.5 State Machines Ex
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Page 115 and 116: Expressions from it. For instance,
Page 117 and 118: Expressions defined. For example, >
Page 119 and 120: Expressions length is given by the
Page 121 and 122: Expressions Thus, for example, you
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Page 125 and 126: Expressions value. For example, fix
Page 127 and 128: Expressions In the example in figur
Page 129 and 130: Expressions A.2 Basic Mathematical
Page 131 and 132: Expressions A.3 Matrix, Array, and
Page 133 and 134: Expressions A.5 Signal Processing F
Page 135 and 136: Expressions TABLE 8: Functions perf
Page 137 and 138: 4 Actor Libraries Authors: Elaine C
Page 139 and 140: Actor Libraries properly in the CT
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Actor Libraries ing that multiple c
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Actor Libraries TypedAtomicActor «
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Actor Libraries SequenceScope (exte
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Actor Libraries UnsignedByteArrayTo
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Actor Libraries MobileFunction (ext
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Actor Libraries LogicFunction (exte
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Actor Libraries Sleep (extends Tran
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Actor Libraries VariableFIR (extend
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Actor Libraries Integrator: Integra
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Actor Libraries Figure 4.4 shows th
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5 Designing Actors Authors: Christo
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Designing Actors /** Javadoc commen
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Designing Actors although with most
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Designing Actors import ptolemy.act
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Designing Actors makes such actors
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Designing Actors same parameter val
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Designing Actors morphic actor comp
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Designing Actors To get data polymo
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Designing Actors public class Seque
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Designing Actors be used in domains
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Designing Actors alComm actor. Beca
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Designing Actors attribute has valu
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Designing Actors import ptolemy.act
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6 Coding Style Authors: Christopher
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Coding Style /* One line descriptio
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Coding Style Copyright (c) 2004 The
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Coding Style @version $Id: NamedObj
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Coding Style } We use instead the i
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Coding Style * @exception MyExcepti
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Coding Style + "it does not impleme
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Authors: Edward A. Lee Steve Neuend
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MoML cutes it forever, until you hi
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MoML A second difference between ou
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MoML
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MoML 7.3.3 Names and Classes Most M
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MoML Here, the element named
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MoML implement. 7.3.7 Doc Element S
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MoML It is also sometimes necess
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MoML then there will be a link t
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MoML found. For example, if the cla
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MoML it cannot collide with the nam
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MoML The rendering of the icon is d
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MoML 7.4.5 Deleting Entities, Relat
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MoML This unlinks a port from the s
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MoML model. The EntityLibrary class
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MoML Suppose that using incremental
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MoML Generate a sine wave.
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MoML
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MoML Number of iterations in
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MoML -P- The f
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MoML -P- The phase,
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8 Custom Applets Authors: Edward A.
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Custom Applets html code, see the J
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Custom Applets public class Tutoria
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Custom Applets then the result of
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Custom Applets 8.3.5 Using Model Pa
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Custom Applets ptolemy/domains/doma
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References [1] G. Agha, Actors: A M
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[33] S. A. Edwards, “The Specific
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[67] E. Kohler, The Click Modular R
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[95] J. Liu, X. Liu, T. J. Koo, B.
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[132]W. R. Sutherland, "The on-Line
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Glossary abstract syntax ..........
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Ptolemy II ........................
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Index Symbols - in UML 41 # in UML
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coin flips 142 Color class 173 colo
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entity in XML 198 EntityLibrary cla
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Director class 159 inverse FFT 124
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CompositeEntity class 206 nextPower
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safety 34 SampleDelay actor 78, 138
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type constraint 155 type constraint
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