Dali: A Gridded Cell Placement Flow

Asynchronous Very-Large-Scale-Integration (VLSI) has several potential benefits over its synchronous counterparts, such as reduced power consumption, elastic pipelining, and robustness to variations. However, the lack of electronic design automation (EDA) support for asynchronous circuits, especially physical layout automation tools, largely limits their adoption. To tackle this challenge, we propose a gridded cell layout methodology for asynchronous circuits, in which the cell height and cell width can be any integer multiple of two grid values. The gridded cell approach combines the shape regularity of standard cells with the size flexibility of custom design, and thus achieves a better space utilization ratio and lower wire-length for asynchronous designs. We present the algorithms and our implementation of Dali, a gridded cell placer, that consists of an analytical global placer, a forward-backward legalizer, an N/P-well legalizer, and a power grid router. We show that the gridded cell placement approach reduces area by 15% without impacting the routability of the design. We have also used Dali to tape out a chip in a 65nm process technology, demonstrating that our placer generates design-rule clean placement.