Realistic Simulations of Embedded Control Systems

Jie Liu, Johan Eker, Jorn W. Janneck, and Edward A. Lee

Presented at the International Federation of Automatic Control
15th IFAC World Congress, Barcelona, Spain, July 21-26, 2002.

Prepublished version
Published version


Current tools for design and implementation of embedded systems lack sufficient support for handling the different development phases. These phases usually include design of control laws, supervision logic, real-time task scheduling, modeling of communication, etc. The heterogeneity of modern embedded control systems puts high demands on design and simulation tools. Many control systems are hybrid in the sense that they consist of a set of subcontrollers and some switching logic. The individual subcontrollers are conveniently described using discrete equations, the switching logic may be expressed using state machines, the complete controller is implemented as a task in a real-time operating system, the controlled plant is modeled as a system of differential equations, and so on. The Ptolemy project addresses the design, simulation and implementation of heterogeneous hierarchical systems. The design principles are demonstrated in the Ptolemy II software which advocates a component-based design methodology, and hierarchically integrates multiple models of computation, which can be used to capture different design perspectives. A Furuta pendulum control system is used as a motivating example. After designing a threemode hybrid controller under idealized assumptions, implementation effects, such as those caused by real-time scheduling and network communication, are taken into consideration to achieve a more realistic simulation. Copyright 2002 IFAC.