Towards High Performance and Accurate BNN Inference on FPGA with Structured Fine-grained Pruning

As the extreme case of quantization networks, Binary Neural Networks (BNNs) have received tremendous attention due to many hardware-friendly properties in terms of storage and computation. To reach the limit of compact models, we attempt to combine binarization with pruning techniques, further exploring the redundancy of BNNs. However, coarse-grained pruning methods may cause server accuracy drops, while traditional fine-grained ones induce irregular sparsity hard to be utilized by hardware. In this paper, we propose two advanced fine-grained BNN pruning modules, i.e., structured channel-wise kernel pruning and dynamic spatial pruning, from a joint perspective of algorithm and hardware. The pruned BNN models are trained from scratch and present not only a higher precision but also a high degree of parallelism. Then, we develop an accelerator architecture that can effectively exploit the sparsity caused by our algorithm. Finally, we implement the pruned BNN models on an embedded FPGA (Ultra96v2). The results show that our software and hardware codesign achieves 5.4x inference-speedup than the baseline BNN, with higher resource and energy efficiency compared with prior FPGA implemented BNN works.