RBSA: Range-based simulated annealing for FPGA placement

Placement has always been the most time-consuming part in the FPGA compilation flow. Traditional simulated annealing has been unable to keep pace with ever increasing sizes of designs and FPGA chip resources. Without utilizing information of the circuit topology, it relies on large amounts of random swap operations, which are time-costly. This paper proposes a range-based algorithm to improve the behavior of swap operations and limit the swap distances by introducing the concept of range limiting for nets. It avoids unnecessary design space exploration, and thus can converge to near-optimal solutions much more quickly. The Titan benchmarks we have tested on contains 4K to 30K blocks, which include LABs, IOs, DSPs and RAMs. This approach achieves 2.05X speed up on average compared with the SA from VTR while preserving the placement quality of both the wire length and critical path. It also manifests better scalability towards larger benchmarks.