Partial Reconfiguration for Design Optimization

FPGA designers have traditionally shared a similar design methodology with ASIC designers. Most notably, at design time, FPGA designers commit to a fixed allocation of logic resources to modules in a design. At runtime, some of the occupied resources could be left under-utilized due to hard-to-avoid sources of inefficiencies (e.g., operation dependencies, unbalanced pipelines). With partial reconfiguration (PR), FPGA resources can be re-allocated over time. Therefore, using PR, a designer can attempt to reduce under-utilization with better area-time scheduling. In this paper, we offer definitions, insights, and equations to explain when, how, and why PR-style designs can improve over the performance-area Pareto front of ASIC-style designs (without PR). We first introduce the concept of area-time volume to explain why PR-style designs can improve upon ASIC-style designs. We identify resource under-utilization as an opportunity that can be exploited by PR-style designs. We then present a first-order analytical model to help a designer decide if a PR-style design can be beneficial. When it is the case, the model points to the most suitable PR execution strategy and provides an estimate of the improvement. The model is validated in a case study.