Using VHDL for high-level, mixed-mode system simulation

The application of a very-high-speed integrated circuit hardware description language (VHDL) to the modeling of complex, application-specific systems that employ a mix of digital hardware and software and interact with their environments through continuous-time components is described. A VHDL model simulating package and a SPICE-like low-level package simulating continuous-time subsystems are discussed. To illustrate how the various packages discussed are used in a complete high-level system simulation, a simplified high-level block diagram of a robot control system is presented, and the modeling of the system is described. Specialized VHDL packages model the system's discrete-time portion as a set of concurrent processes communicating via channels with well-defined protocols, and sets of coupled ordinary differential equations model the system's continuous-time blocks.<<ETX>>