ECO algorithms for removing overlaps between power rails and signal wires

Design ECO commonly happens in industry due to constraints or target changes from manufacturing, marketing, reliability, or performance. At each step, designers usually want to modify the existing solution incrementally and keep the design as close as possible to the existing one. In this paper, we address the PSO (Power rail - Signal wire Overlap) problem which solves overlaps between power rails and signal wires due to the changes in power rail design on the top layer of a multiple layer routing region. PSO problems are frequently caused by changes from power delivery system or package design. The new routing solution satisfies the following constraints: 1) Keep the routing of power rails in the new design unchanged. 2) Only the routing of the top two layers is changed. 3) Horizontal (vertical) signal wire segments on the top layer can only move up/down (left/right). At the same time, the new routing solution keeps the routing pattern unchanged. This requires: a) If one end point of a horizontal (vertical) wire segment on the top layer is a fixed pin, this segment can not move. b) if vertical (horizontal) projections of two horizontal (vertical) signal wire segments have overlaps, then the up/down (left/right) relationship should not be changed. c) If two horizontal (vertical) segments belonging to different nets are on the same track, their left/right (up/down) relationship should not be changed as long as the two segments still exist in the new solution. 4) For each signal wire segment, the deviation (i.e., the difference between its new position and the old one) should not exceed the user-defined allowable deviation bound. Different bounds can be set on different segments. We propose two algorithms to solve the PSO problem. Both algorithms guarantee to find a feasible solution as long as one exists. One is faster, while the other makes effort to minimize the total deviation as well as the max deviation. According to time and quality requirements, users can choose an appropriate algorithm to solve the problem. For a set of industrial test circuits, we were able to remove all overlaps between power rails and signal wires with minimal wire deviation.