Multi-pumping for resource reduction in FPGA high-level synthesis

Resource sharing is a classic high-level synthesis (HLS) optimization that saves area by mapping multiple operations to a single functional unit. With resource sharing, only operations scheduled in separate cycles can be assigned to shared hardware, which can result in longer schedules. In this paper, we propose a new approach to resource sharing that allows multiple operations to be performed by a single functional unit in one clock cycle. Our approach is based on multi-pumping, which operates functional units at a higher frequency than the surrounding system logic, typically 2x, allowing multiple computations to complete in a single system cycle. Our approach is particularly effective for DSP blocks on an FPGA, which are used to perform multiply and/or accumulate operations. Our results show that resource sharing using multi-pumping is comparable to traditional resource sharing in terms of area saved, but provides significant performance advantages. Specifically, when targeting a 50% reduction in DSP blocks, traditional resource sharing decreases circuit speed performance by 80%, on average, whereas multi-pumping decreases circuit speed by just 5%. Multi-pumping is a viable approach to achieve the area reductions of resource sharing, with considerably less negative impact to circuit performance.