Design re-use for compile time reduction in FPGA high-level synthesis flows

Abstract

High-level synthesis (HLS) raises the level of abstraction for hardware design through the use of software methodologies. An impediment to productivity in HLS flows, however, is the run-time of the back-end toolflow - synthesis, packing, placement and routing - which can take hours or days for the largest designs. We propose a new back-end flow for HLS that makes use of pre-synthesized and placed "macros" for portions of the design, thereby reducing the amount of work to be done by the back-end tools, lowering run-time. A key aspect of our work is an analytical placement algorithm capable of handling large macros whose internal blocks have fixed relative placements, in conjunction with placing the surrounding individual logic blocks. In an experimental study, we consider the impact on run-time and quality-of-results of using macros: 1) in synthesis alone, and 2) in synthesis, packing and placement. Results show that the proposed approach reduces run-time by ~3x, on average, with a negative performance impact of ~5%.