FAR: fixed-points addition & relaxation based placement

In this paper we describe the Fixed-points Addition and Relaxation (FAR) based placement technique. Fixed point is a pseudo cell connected to a movable cell. By introducing fixed points, the placement can be maintained in a force equilibrium state and further transformed into another equilibrium state. By relaxing some of the previously introduced fixed points, we can partially or completely collapse the current placement in order to reposition the cells, or incrementally perturb the existing good solution to fulfill additional requirements. We apply the FAR-based approach to global placement for total wire length minimization, and to incremental placement for Buffer Site Generation (BSG). For global placement, our experimental results show that the FAR method achieves 54.4% CPU speedup and total wire length comparable to that achieved by the constant force based approach [1]. Experimental results indicate that to accommodate buffers in specific regions, FAR is able to perturb incrementally a given solution in a well-controlled way.