Alignment net insertion for straightening the datapath in a force-directed placer

摘要

An automated method for aligning a critical datapath in an integrated circuit design inserts an artificial alignment net in the netlist which interconnects all cells in the bit stack of the datapath. The cells are placed using a wirelength optimization which assigns weights to wire sections based on the alignment direction. The rate of change of the alignment weighting value can vary during different stages of global placement. The invention is particularly suited for a force-directed placer which uses a linear system solver to obtain a globally optimum solution for placement of the cells having some overlap among the cells, and thereafter spreads the cells to reduce the overlap. Pseudo nets are also inserted which interconnect a cell and an expected location of the cell after spreading for that iteration.

主权项

1. A method of placing cells in a layout of an integrated circuit design, comprising:
receiving a circuit description of the integrated circuit design which includes a plurality of cells interconnected to form a plurality of true nets, by executing first instructions in a computer system; designating a preferred direction for cell alignment in the layout, by executing second instructions in the computer system; identifying a set of the cells defining a datapath which is to be aligned along the preferred direction, by executing third instructions in the computer system; inserting in the circuit description an artificial alignment net which interconnects all cells in the set, by executing fourth instructions in the computer system; and placing the cells in the layout of the integrated circuit design using a wirelength optimization which assigns weights to wire sections of nets based on the preferred direction, by executing fifth instructions in the computer system.