Algorithms for non-Hanan-based optimization for VLSI interconnect under a higher-order AWE model

摘要

To improve the performance of critical nets where both timing and wire resources are stringent, we integrate buffer insertion and driver sizing separately with non-Hanan optimization and propose two algorithms: simultaneous buffer insertion and non-Hanan optimization (BINO) and full-plane AWE routing with driver sizing (FAR-DS). For BINO, we consider the realistic situation that buffer locations are restricted to a limited set of available spaces after cell placement. The objective of BINO is to minimize a weighted sum of wire and buffer costs subject to timing constraints. To achieve this objective, we suggest a greedy algorithm that considers two operations independently: iterative buffer insertion and iterative buffer deletion. Both are conducted simultaneously with non-Hanan optimization until the improvement is exhausted. For FAR-DS, we investigate the curvature property of the sink delay as a function of both connection location and driver stage ratio in a two-dimensional (2-D) space. The objective of FAR-DS is to minimize a weighted sum of wire and driver cost while ensuring that the timing constraints are satisfied. Based on the curvature property, we search for the optimal solution in the continuous 2-D space. In both BINO and FAR-DS, a fourth-order AWE delay model is employed to assure the quality of optimization. Experiments of BINO and FAR-DS on both integrated circuit and MCM technologies showed significant cost reductions compared with SERT and MVERT in addition to making the interconnect to satisfy timing constraints.