A Memory-Access-Minimized BCNN Accelerator Using Nonvolatile FPGA with Only-Once- Write Shifting

A binary convolutional neural network (BCNN) accelerator using a nonvolatile field-programmable gate array (NV-FPGA) with only-once-write shifting is presented. During the basic operation of the BCNN, the feature maps and weights are read from the block RAM (BRAM) and serially transferred to processing elements. The use of only-once-write shifting makes it possible to greatly reduce write power consumption such serial data transfer in the NV-FPGA. Meanwhile, since the BCNN computing is composed of the nested loop, the memory access potentially has a temporal locality. This means that once the data is read from the BRAM, it can be reused among several layers. By focusing this feature and performing loop interchange, the number of memory access can be minimized and the idle time is maximized. If the BRAM is nonvolatile, wasted standby energy consumption during idle state is completely eliminated by the use of power gating technique. As a result, the proposed BCNN accelerator is 66.5% lower energy consumption than a conventional volatile-FPGA-based BCNN accelerator in typical digit recognition task with MNIST dataset.