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Chapter 10. SR domain

Authors: Stephen Edwards

Other Contributors: Christopher Hylands

Mary Stewart

10.1 Introduction

The Synchronous Reactive domain is a statically-scheduled simulation domain in

Ptolemy designed for concurrent, control-dominated systems. To allow precise control over

timing, it adopts the synchronous model of time, which is logically equivalent to assuming

that computation is instantaneous.

10.2 SR concepts

Time in the SR domain is a sequence of instants. In each instant, the system observes

its inputs and computes its reaction to them. Each instant is assumed to take no time at all. All

computation is treated as being instantaneous.

Communication in the SR domain takes place through unbuffered single driver, multi-

ple receiver channels. In each instant, each channel may have a single event with a value, have

no event, or be undeﬁned, corresponding to the case where the system could not decide

whether the channel had an event or not. Communication is instantaneous, meaning that if an

event is emitted on a channel in a certain instant, every star connected to the channel will see

the event in the same instant.

10.3 SR compared to other domains

SR is similar to existing Ptolemy domains, but differs from them in important ways.

Like Synchronous Dataﬂow (SDF), it is statically scheduled and deterministic, but it does not

have buffered communication or multi-rate behavior. SR is better for control-dominated sys-

tems that need control over when things happen relative to each other; SDF is better for data-

dominated systems, especially those with multi-rate behavior.

SR also resembles the Discrete Event (DE) domain. Like DE, its communication chan-

nels transmit events, but unlike DE, it is deterministic, statically scheduled, and allows zero-

delay feedback loops. DE is better for modeling the behavior of systems (i.e., to better under-

stand their behavior), whereas SR is better for specifying a system’s behavior (i.e., as a way to

actually build it).

10.4 The semantics of SR

An SR star must be well-behaved in the following mathematical sense to make SR sys-

tems deterministic. It must compute a monotonic function of its inputs, meaning that when it

is presented with more-deﬁned inputs, it must produce more-deﬁned outputs. In particular, an

output may only switch from undeﬁned to either present or absent when one or more inputs

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Résumé du contenu

Page 1 - Chapter 10. SR domain

Chapter 10. SR domainAuthors: Stephen EdwardsOther Contributors: Christopher HylandsMary Stewart10.1 IntroductionThe Synchronous Reactive domain is

Page 2 - 10-2 SR domain

10-2 SR domainU. C. Berkeley Department of EECSdo, but it may not change its value or become undeﬁned.The semantics of SR are deﬁned as the least ﬁxed

Page 3 - 10.5 Overview of SR stars

The Almagest 10-3Ptolemy Last updated: 12/1/9710.5 Overview of SR starsThe top-level palette is shown in ﬁgure 10-1.10.5.1 General starsConst Output

Page 4 - 10-4 SR domain

10-4 SR domainU. C. Berkeley Department of EECSPrinter Print the value of each input to the ﬁle speciﬁed by the ﬁleNamestate. All inputs are printed o

Page 5 - 10.6 An overview of SR demos

The Almagest 10-5Ptolemy Last updated: 12/1/97EnvelopeGen An envelope generator for FM sound synthesis.10.6 An overview of SR demosThere are currentl

Page 6 - 10-6 SR domain

10-6 SR domainU. C. Berkeley Department of EECS*Note that it is necessary to have functioning CGC audio drivers in order to demo theSR stars written f