Create_fp_placement中的-no_hierarchy_gravity,按说明是:Prevents the grouping of cells within the same hierarchal block,阻止相同Hierarchy Block的cell放置在一起(不知道是不是我的理解有问题)。
为什么在User Guide中有这么一段话:
For better results, observe the following guidelines for virtual flat placement:
Disable the hierarchical gravity feature by using create_fp_placement
-no_hierarchy_gravity if the design does not have hierarchy