Virtual Interface

Abstract

In most hierarchical compaction systems, including HPMC, the connectivity is implicit in the symbolic layout. Connectivity is extracted from the symbolic layout based on the input topology and is preserved during the compaction process. This is true for both connectivity inside leaf cells as well as the hierarchical connectivity across cells. This implicit representation of connectivity in the symbolic layout causes geometric information to creep into the symbolic layout. Though this may be acceptable for leaf cells, it has serious drawbacks in designing hierarchical layouts and significantly reduces the effectiveness of the symbolic methodology. When leaf cells are designed for use in hierarchical layouts, the position of pins or ports in these cells that connect to other cells is constrained by the abutment requirements. This is because when cells are placed in a particular configuration, the connectivity across cells is implicit by the overlapping of symbols. Hence the pin or port positions for the cells must be decided before the actual symbolic layout of leaf cells, which can lead to sub-optimum designs.