考虑重叠度和线长的单元密度平滑方法

Density Smoothing Method Considering Wire-Length and Overlap

针对目前力指向布局中单元移动式的密度平滑方法存在对优化结果破坏较大、收敛速度较慢的缺点,提出一种考虑重叠度和线长的密度平滑方法(DSAW).该方法结合局部和全局的密度分布来确定单元移动距离,使单元移动中尽量减少对线长的破坏;同时对面积大的单元进行了离散化处理,通过矢量求和来确定大单元的移动距离,减少计算误差.将DSAW嵌入到使用基于扩散的密度平滑方法(DPlace)布局器中的实验结果表明,与DPlace相比,文中方法使线长降低7%,总体运行时间有明显的提高.

Current cell migration methods used in force directed analytical placement have deficiency of damaging the results of last iterative placement and influencing the speed of convergence. In this paper, a new density smoothing technique called DSAW （density smoothing aware of wire-length） is presented. DSAW obtains the moving distance by both of the local and the global density distribution while considering the wire-length and overlap simultaneously, and tries to reduce the damage to the wire-length caused by cell migration. The standard cells and the macro blocks crossing multi-bin are separated and by summing the shifting vectors of the discrete modules so as to get a more smooth speed. DSAW is embedded into the global placement process of DPlace and replaces the original diffusion smoothing method, and experimental results show that average HPWL （half perimeter wire-length） reduces 7% and the total runtime is faster than original DPlace.