Abstract
In current industrial design methodologies, designers often take advantage of using spare cells when they have to make some functional changes or fix timing problems. However, the methodology of realizing functional changes by using spare cells is very complex and difficult. It could consist of two steps – technology mapping and spare cell selection. Traditional technology mapping only maps functions into the cells in a library without considering any resource constraint, so it is not suitable for this methodology. After technology mapping, how to make selections on spare cells is also an important issue, because bad selections will seriously impact the result. In this paper, we study the problem of functional changes using spare cells, and present an approach to efficiently solve the problem with the goal of minimizing the increase in wirelength. Our approach consists of a technology mapping method and a legalization method that both work together to generate the initial selection on spare cells, followed by a refinement process that is used to improve the selection with further reduction in wirelength increase. We also propose two methods for the refinement process. The experimental results are given to demonstrate the effectiveness and efficiency of our approach.