Specification of Control Flow in Ptolemy
Bilung Lee, Xiaojun Liu|
|Advisor:||Edward A. Lee|
Most modern systems include control functionality for the proper
sequencing of the computation tasks, and switching and coordinating between
different operation modes. Finite state machines (FSMs) have long
been used to specify control flow for control-dominated problems. In large
systems, however, the control functionality can become so complex that the
flat, sequential FSM model becomes impractical.
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  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 , discrete events  and synchronous/reactive 
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  domain in Ptolemy II.
- D. Harel, "Statecharts: A Visual Formalism for Complex Systems,"
Science of Computer Programming, vol. 8, pp. 231-274, 1987.
- J. B. Dennis, "First Version Data Flow Procedure Language",
Technical Memo MAC TM61, May, 1975, MIT Laboratory for Computer Science.
- C. Cassandras, "Discrete Event Systems, Modeling and Performance
Analysis," Irwin, Homewood IL, 1993.
- A. Benveniste and G. Berry, "The Synchronous Approach to Reactive and
Real-Time Systems," Proceedings of the IEEE, Vol. 79, No. 9, 1991,
- 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).
Last updated 03/22/99