Modular nets (MNETS): A modular design methodology for computer timers

This paper describes a modular, graphical, fully implemented CAD tool for building timers to model computer pipelines. The complete system is composed of three parts which can exist independently but have been fully integrated to provide a user-friendly CAD tool. These parts are, first, modular nets (MNETS), a new modeling concept for modular, graphical implementation of pipeline structures of any kind; second, the implementation of various MNETS modules and macros in a VHDL library similar to logic and circuit design libraries; and third, the integration of parts 1 and 2 into an existing graphical entry framework, the EDA Wizard graphical editor. A graphical model is constructed by interconnecting basic building blocks using the graphical tool, similarly to the way circuits and logic are designed. Selection of a menu option will produce a VHDL description of this graphical model, which can subsequently be simulated on a VHDL simulator. This paper concentrates on part 1, the features of MNETS which make it inherently modular and consequently graphical. The two crucial requirements, namely the construct for storing of state and a control mechanism for the passing of state, are unique to MNETS and are discussed in detail, with comparisons to other methodologies. A brief discussion of some features and macros available in the existing MNETS library is included, as well as one simple modeling example. This library can be accessed on the IBM Andrew file system, AFS. A detailed MNETS user/design manual is available which describes MNETS in detail, as well as the library, memory hierarchy design, and modeling.