An Efficient Algorithm for Local Don't Care Sets Calculation

Local don't cares of an internal node expressed in terms of its immediate inputs are usually of interest. One can directly apply any two-level minimizer on the on-set and the local don't cares set to simplify an internal node. In this paper, we propose a memory efficient technique to calculate local don't cares of internal nodes in a combinational circuit. Our technique of calculating local don't cares makes use of automatic test pattern generation (ATPG) approach which allows us to identify quickly whether a cube in the local space is a don't care or not. Unlike other approaches which construct an intermediate form of don't cares in terms of the primary inputs, our technique directly computes the don't care cubes in the local space. This gives us a significant advantage over the previous approaches in memory usage. Experimental results on MCNC benchmarks are very encouraging.