An optimized buffer insertion algorithm with delay-power constraints for VLSI layouts

Authors: CHESSDA UTTRAPHAN, NASIR SHAIKH-HUSIN, MOHAMED KHALIL HANI

Abstract: We propose a grid-graph algorithm for interconnect routing and buffer insertion in nanometer VLSI layout designs. The algorithm is designed to handle multiconstraint optimizations, namely timing performance and power dissipation. The proposed algorithm is called HRTB-LA, which stands for hybrid routing tree and buffer insertion with look-ahead. In recent VLSI designs, interconnect delay has become a dominant factor compared to gate delay. The well-known technique to minimize the interconnect delay is by inserting buffers along the interconnect wires. However, the buffer itself consumes power and it has been shown that power dissipation overhead due to buffer insertions is significantly high. Many methodologies to optimize timing performance with power constraint have been proposed, and no algorithm is based on dynamic programing technique using a grid graph. In addition, most of the algorithms for buffer insertion use a postrouting buffer insertion approach. In the presence of buffer obstacles, these postrouting algorithms may produce poor solutions. On the other hand, the simultaneous routing and buffer insertion algorithm offers a better solution, but it was proven to be NP complete. Hence, our main contribution is an efficient algorithm using a hybrid approach for multiconstraint optimization for multisink nets. The algorithm uses dynamic programming to compute incrementally the interconnect delay and power dissipation of the inserted buffers while an effective runtime is achieved with the aid of novel look-ahead and graph pruning schemes. Experimental results prove that HRTB-LA is able to handle multiconstraint optimizations and produces a solution up to 30% better compared to a postrouting buffer insertion algorithm in comparable runtime.

Keywords: Buffer insertion, dynamic programming, VLSI routing optimization, VLSI design automation, power dissipation

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