A three-layer over-the-cell multi-channel router for a new cell model

Abstract

This paper proposes a new cell model for over-the-cell routing, and presents a heuristic three-layer over-the-cell multi-channel routing method for the new cell model. In the proposed cell model, terminals can be placed arbitrarily on the second metal (M2) layer of a cell so that each cell does not require the extra routing region on the first metal (M1) layer of a cell to align terminals. Unlike conventional cell models, some parts of the M2 layer may also be utilized for intra-cell routing in order to reduce the chip area. Therefore the size of a cell with the proposed cell model can be smaller than that with conventional cell models. The proposed three-layer over-the-cell routing method consists of three phases. In order to utilize the proposed cell model effectively, in phase 1, we simultaneously handle all channels to determine the most effective routing patterns from the set of possible routing patterns to minimize the chip area. In phase 2, for the routing patterns of nets selected in phase 1, over-the-cell routing nets are selected by a new greedy algorithm considering obstacles in over-the-cell regions. Finally, in phase 3, the conventional three-layer channel routing algorithm is applied for remaining nets. From the experimental results with MCNC benchmarks, the proposed cell model and routing algorithm produce the smaller height of layouts as compared to those produced by conventional cell models and algorithms, and the effectiveness of the proposed cell model and routing method was shown.