Clock-Aware Placement for Large-Scale Heterogeneous FPGAs

A modern field-programmable gate array (FPGA) often contains an ASIC-like clocking architecture which is crucial to achieve better skew and performance. Existing conventional FPGA placement algorithms seldom consider clocking resources, and thus may lead to clock routing failures. To address the special FPGA clocking architecture, this article presents an effective clock-aware placement algorithm for large-scale heterogeneous FPGAs. Our algorithm consists of four major technologies: 1) a combinatorial clock fence region method to effectively reduce the overuse of clocking resources; 2) a smoothed heterogeneous density function to lead heterogeneous blocks to desired sites and a coordinate transformation technique to facilitate CLB cell spreading; 3) a heterogeneous force modulation algorithm to stabilize placement movement and a hierarchical contraction technique to remedy an insufficiency of the multilevel placement framework; and 4) a two-level clock-aware packing and legalization scheme to generate an optimized, clocking-violation-free placement. We evaluate our results based on the ISPD 2017 Clock-Aware Placement Contest benchmark suite. Compared with the state-of-the-art placers, the experimental results show that our algorithm achieves the best-routed wirelength.