A scalable routability-driven analytical placer with global router integration for FPGAs (abstract only)

Abstract

As the sizes of modern circuits become bigger and bigger, implementing those large circuits into FPGA becomes arduous. The state-of-the-art academic FPGA place-and-route tool, VPR, has good quality but needs around a whole day to complete a placement when the input circuit contains millions of lookup tables, excluding the runtime for routing. To expedite the placement process, we propose a routability-driven placement algorithm for FPGA that adopts techniques used in ASIC global placer. Our placer follows the lower-bound-and-upper-bound iterative optimization process in ASIC placers like Ripple. In the lower-bound computation, the total HPWL, modeled using the Bound2Bound net model, is minimized using the conjugate gradient method. In the upper-bound computation, an almost-legalized result is produced by spreading cells linearly in the placement area. Those positions are then served as fixed-point anchors and fed into the next lower-bound computation. Furthermore, global routing will be performed in the upper-bound computation to estimate the routing segment usage, as a mean to consider congestion in placement. We tested our approach using 20 MCNC benchmarks and 4 large benchmarks for performance and scalability. Experimental results show that based on the island-style architecture which VPR is most optimized for, our approach can obtain a placement result 8x faster than VPR with 2% more in channel width, or 3x faster with 1% more in channel width when congestion is being considered. Our approach is even 14x faster than VPR in placing large benchmarks with over 10,000 lookup tables, with only 7% more in channel width.