Bitwidth-optimized hardware accelerators with software fallback

We propose the high-level synthesis of an FPGA-based hybrid computing system, where the implementations of compute-intensive functions are available in both software, and as hardware accelerators. The accelerators are optimized to handle common-case inputs, as opposed to worst-case inputs, allowing accelerator area to be reduced by 28%, on average, while retaining the majority of performance advantages associated with a hardware versus software implementation. When inputs exceed the range that the hardware accelerators can handle, a software fallback is automatically triggered. Optimization of the accelerator area is achieved by reducing datapath widths based on application profiling of variable ranges in software (under typical datasets). The selected widths are passed to a high-level synthesis tool which generates the accelerator for a given function. The optimized accelerators with software fallback capability are generated automatically by our framework, with minimal user intervention. Our study explores the trade-offs of delay and area for benchmarks implemented on an Altera Cyclone II FPGA.