V-FPGAs: Increasing Performance with Manual Placement, Timing Extraction and Extended Timing Modeling

Virtual FPGAs (V-FPGAs) are used as vendor-independent virtualization layers, to retrofit features which are not available on the host FPGA and to prototype novel FPGA architectures. In these usecases, the achievable clock frequencies of V-FPGA user applications are a major concern. The abstraction layer inherently induces overhead, but this aspect is reinforced by nonuniformity effects: When V-FPGA cells perform worse locally, basic architecture modeling generalizes these worst-case path delays to the whole device, limiting applications to a lower frequency than theoretically achievable. We propose three approaches to attenuate these effects: First we introduce uniformity metrics and manual V-FPGA placement strategies for more uniform placement, improving achievable frequency by 16 %. Second, we propose a framework for automated timing extraction, enabling individual characterization of each V-FPGA design. Third, after evaluating Vivado synthesis strategies, we extend the timing model for non-uniform timings, achieving improvements of up to 28 %.