System-Level Modeling of Continuous and Discrete Dynamics
Jie Liu, UC Berkeley

Complex systems like mixed-signal electronic systems, micro electro-mechanical systems (MEMS), and real-time control systems, contain both continuous and discrete dynamics. Typically, continuous dynamics take the form of ordinary differential equations (ODEs) and discrete dynamics may be in the form of a discrete-event model or finite state machines. Such systems are modeled in Ptolemy II using hierarchical heterogeneous components in the continuous time (CT), discrete event (DE), and finite state machine (FSM) domains.

In order to achieve a correct simulation of such systems, it is essential for the continuous-time simulation engine to have the ability to detect and handle discrete events. The central part of this work is the study of the formal semantics of the models and their interaction, including causality, determinacy, fixed-point behavior, event detection and signal conversions.

The semantics study also yields a deep insight into the interaction of heterogeneous (simulation) CAD tools. We are developing a methodology that classifies existing CAD tools by their underlying models of computation (MoC), and embeds CAD tools only in the Ptolemy II domains that have the same MoC. Ptolemy II acts as the standard semantic glue for the external tools. Thus, for example, a digital hardware simulation tool based on Verilog or VHDL can interact with an analog simulation tool such as Saber through a Ptolemy II backplane.