Software Structuring Principles for VLSI CAD,

VLSI CAD systems are typically large and undergo frequent changes. Such systems should be designed for reusability by anticipating change. Our thesis is that this goal can be achieved by designing the software as layers of problem oriented languages, which are implemented by suitably extending a base language. A language layer rarely needs to be adapted to changes, only the application i.e. algorithm needs to be changed. We present and compare two different implementations of this philosophy. The first uses UNIX and Enhanced C and the second uses Common Lisp on a Lisp machine. In each case, we describe the basic technique and its applications.