A Component-Based Approach to Modeling and Simulating Mixed-Signal and Hybrid Systems

Jie Liu and Edward A. Lee

ACM Trans. on Modeling and Computer Simulation special issue on computer automated multi-paradigm modeling, Volume 12, Issue 4, pp. 343-368, October 2002.

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Systems with both continuous and discrete behaviors can be modeled using a mixed-signal style or a hybrid systems style. This paper presents a component-based modeling and simulation framework that supports both modeling styles. The component framework, based on an actor meta-model, takes a hierarchical approach to manage heterogeneity in modeling complex systems. We describe how ordinary differential equations, discrete-event systems, and finite state machines can be built under this meta-model. A mixed-signal system is a hierarchical composition of continuous-time and discrete-event models, and a hybrid system is a hierarchical composition of continuous-time and finite-state-machine models. Hierarchical composition and information hiding help building clean models and efficient execution engines. Simulation technologies, in particular, the interaction between a continuous-time ODE solving engine and various discrete simulation engines are discussed. A signal type system is introduced to schedule hybrid components inside a continuous-time environment. Breakpoints are used to control the numerical integration step sizes so that discrete events are handled properly. A “refiring” mechanism and a “rollback” mechanism are designed to manage continuous components inside a discrete-event environment. The technologies are implemented in the Ptolemy II software environment. Examples are given to show the applications of this framework in mixed-signal and hybrid systems.