Integrating LR Gate Sizing in an Industrial Place-and-Route Flow
David Chinnery, Ankur Sharma · 2022
Lagrangian relaxation (LR) based gate sizing is the state-of-the-art gate-sizing approach. Integrating it within a place-and-route (P&R) tool is difficult as LR needs multiple iterations to converge, requiring very fast timing analysis. Gate-sizing is invoked in many P&R flow steps, so it is also unclear where best to use LR sizing. We detail development of a LR gate sizer for an industrial P&R flow. Software architecture and P&R flow needs are discussed. We summarize how we sped up the LR sizer by 3x to resize a million gates per hour, and ensure multi-threaded results are deterministic. LR sizing experiments at the fast WNS/TNS optimization steps in the flow stages before and after clock tree synthesis (CTS) show excellent results: 10% to 20% setup timing total negative slack (TNS) reduction with 11% to 14% less leakage power, or 1% to 3% lower total power (dynamic power + leakage) with a total power objective, and 1% to 3% lower cell area. Worst negative slack (WNS) also improved in 2/3 of designs in pre-CTS. In the full flow, 5% lower leakage, 1% lower total power, and 0.6% lower cell area can be achieved, with roughly neutral impact on other metrics, compared to a high-effort low-power P&R flow baseline.