Timing Driven Placement for Large Standard Cell Circuits

Abstract

We present an algorithm for accurately controlling delays during the placement of large standard cell integrated circuits. Previous approaches to timing driven placement could not handle circuits containing 20,000 or more cells and yielded placement qualities which were well short of the state of the art. Our timing optimization algorithm has been added to the placement algorithm which has yielded the best results ever reported on the full set of MCNC benchmark circuits, including a circuit containing more than 100,000 cells. A novel pinpair algorithm controls the delay without the need for user path specification. The timing algorithm is generally applicable to hierarchical, iterative placement methods. Using this algorithm, we present results for the only MCNC standard cell benchmark circuits (fract, struct, and avq.small) for which timing information is available. We decreased the delay of the longest path of circuit fract by 36% at an area cost of only 2.5%. For circuit struct, the delay of the longest path was decreased by 50% at an area cost of 6%. Finally, for the large (22,000 cell) circuit avq.small, the longest path delay was decreased by 28% at an area cost of 6% yet only doubling the execution time. This is the first report of timing driven placement results for any MCNC benchmark circuit.