Figure 1: The input for a fixed cell (top) and a flexible cell with
the shape-function (bottom)
The input to the layout generation process for macro-cell layouts is a set of modules, which are rectangular blocks. Each module represents a functional unit which consists of hierarchically arranged subcells. There are two kinds of modules (cf. fig. 1): A fixed module has fixed dimensions with exact terminal positions for the interconnection nets on its borders (fig. 1, top). A flexible module can have various implementations with different aspect ratios, which are defined by a shape-function. This is a step-function which is characterized by a set of minimal width/height combinations (fig. 1, bottom). For the interconnection nets of a flexible module, only a list of terminals for each side is given but no exact terminal positions, because these vary with the different implementations.