Rapid Overlay Builder for Xilinx FPGAs

Overlays are emerging as useful design patterns for solving reconfigurable computing problems. Overlays consist of compiler-like tools and an architecture written in RTL, making it easier for users to quickly compile high-level languages into FPGAs. Despite a high degree of regularity and repetition present in most overlays, it takes a long time for FPGA tools to generate the configuration bit stream. This paper proposes a methodology called Rapid Overlay Builder, or ROB, that combines module relocation, module variants and an efficient form of "router less" module stitching that we call zipping. Our case study demonstrates up to 22 times speedup in compile-time over a regular Xilinx ISE compilation, while achieving higher clock speeds. By applying ROB, we anticipate that overlays can be implemented more quickly and with more consistent clock rates.