Graph-Based Approaches to Placement of Processing Element Networks on FPGAs for Physical Model Simulation

Abstract

Physical models utilize mathematical equations to characterize physical systems like airway mechanics, neuron networks, or chemical reactions. Previous work has shown that field programmable gate arrays (FPGAs) execute physical models efficiently. To improve the implementation of physical models on FPGAs, this article leverages graph theoretic techniques to synthesize physical models onto FPGAs. The first phase maps physical model equations onto a structured virtual processing element (PE) graph using graph theoretic folding techniques. The second phase maps the structured virtual PE graph onto physical PE regions on an FPGA using graph embedding theory. A simulated annealing algorithm is introduced that can map any physical model onto an FPGA regardless of the model's underlying topology. We further extend the simulated annealing approach by leveraging existing graph drawing algorithms to generate the initial placement. Compared to previous work on physical model implementation on FPGAs, embedding increases clock frequency by 25% on average (for applicable topologies), whereas simulated annealing increases frequency by 13% on average. The embedding approach typically produces a circuit whose frequency is limited by the FPGA clock instead of routing. Additionally, complex models that could not previously be routed due to complexity were made routable when using placement constraints.