Spare Cells With Constant Insertion for Engineering Change

Engineering change (EC) is the process of modifying a VLSI design implementation to eliminate design errors, to add new specifications, or to correct design constraint violations. Usually, an EC problem is resolved by using spare cells that have been inserted into unused spaces on a chip. In this paper, we describe an iterative method to determine feasible mapping solutions for an EC problem considering spare cells whose inputs can be connected to Vdd or Gnd . Setting some of the cell inputs to fixed values is referred to as constant insertion. Constant insertion can increase cells´ functional flexibility. Our experimental results suggest that constant insertion reduces the area required to find a feasible mapping solution to 80% of that with no constant insertion for the selected EC equations. We also show a procedure for modifying the initial feasible EC solution such that the routing or timing improves.