Specification of Control Flow in Ptolemy

Hierarchical concurrent FSMs (HCFSMs) increase the usefulness of FSMs by extending with structuring and communication mechanisms. However, most formalisms that support HCFSMs, such as Statecharts [1] and its variants, tightly integrate the concurrency semantics with the FSM semantics. In contrast, we add hierarchy and heterogeneity to the FSM. This allows the FSM to be hierarchically combined with various concurrency models, in particular dataflow [2], discrete events [3] and synchronous/reactive [4] models. In this heterogeneous model, the semantics of FSM, concurrency and hierarchy are naturally supported. Our scheme decouples the FSM from the concurrency models, enabling selection of the most appropriate concurrency model for the problem at hand.

An FSM domain has been developed in Ptolemy and is integrated with the existing SDF and DE domains. Continuing work is to integrate the FSM domain with the SR domain. In addition, we will use the infrastructure of the FSM domain as our prototype to build a new *chart [5] domain in Ptolemy II.

[1]

D. Harel, "Statecharts: A Visual Formalism for Complex Systems," Science of Computer Programming, vol. 8, pp. 231-274, 1987.

[2]

J. B. Dennis, "First Version Data Flow Procedure Language", Technical Memo MAC TM61, May, 1975, MIT Laboratory for Computer Science.

[3]

C. Cassandras, "Discrete Event Systems, Modeling and Performance Analysis," Irwin, Homewood IL, 1993.

[4]

A. Benveniste and G. Berry, "The Synchronous Approach to Reactive and Real-Time Systems," Proceedings of the IEEE, Vol. 79, No. 9, 1991, pp. 1270-1282.

[5]

A. Girault, B. Lee, and E. A. Lee, "Hierarchical Finite State Machines with Multiple Concurrency Models," April 13, 1998 (revised from Memorandum UCB/ERL M97/57, Electronics Research Laboratory, University of California, Berkeley, CA 94720, August 1997).