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Keep it Straight: Teaching Placement how to Better Handle Designs with Datapaths. Samuel I. Ward†, Myung-Chul Kim‡, Natarajan Viswanathan , Zhuo Li, Charles Alpert, Earl E. Swartzlander , Jr., David Z. Pan ECE Dept. The University of Texas at Austin IBM Austin Research Laboratory.
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Keep it Straight: Teaching Placement how to BetterHandle Designs with Datapaths Samuel I. Ward†, Myung-Chul Kim‡, NatarajanViswanathan, Zhuo Li, Charles Alpert, Earl E. Swartzlander, Jr., David Z. Pan ECE Dept. The University of Texas at Austin IBM Austin Research Laboratory
Outline • Introduction • Motivation • Approach • Experimental results • Conclusion
Introduction • most state-of-the-art placers- HPWL-driven- not structured-aware • StWL correlates with routed wire length much better than HPWL.[18] • Alignment of the datapath cells guides indirect StWL optimization
Motivation • We can teach these HPWL-driven placer to make them structure-aware • Alignment of Datapath cells can implicitly improve StWL
Approach • In this work, a force-directed global placer in the spirit of SimPL is used along with a detailed placer similar to FastPlace-DP.
Alignment net • Very similar to pseudo net in SimPL • These nets are created at the beginning of global placement and remain persistent during the entire global and detailed placement stages.
Fixed-point Alignment Constraint • Lookahead legalization generates a fixed-point location for all cells. • For all cells in datapath group, modify the fixed-point locations.
Aligned DatapathCell Swapping • This work, unlike [20], bounds the swap region perpendicular to dkwhile keeping the overlap penalty the same.
Datapath Group Repartitioning • This technique minimizes internal net cut values potentially improving both HPWL and StWL. • The base cut algorithm is from KL[24].
Conclusion • Presents a unified framework to enhance current random logic placers to better handle designs containing datapath logics. • A set of new global and detail placement techniques were presented to overcome the shortcomings of the HPWL model for datapaths. • Experimental results have great improvement in StWL.
