Resistive random access memory (RRAM) has been demonstrated to implement multiply-and-accumulate (MAC) operations using a highly parallel analog fashion, which dramatically accelerates the convolutional neural networks (CNNs). Since CNNs require considerable converters between analog crossbars and digital peripheral circuits, recent studies map the binary neural networks (BNNs) onto RRAM and binarize the weights to {+1, -1}. However, two mainstream representations for BNN weights introduce patterns of redundant 0s and 1s when dealing with negative weights. In this work, we reduce the area of redundant 0s and 1s by proposing a BNN weight representation framework based on the novel pattern representation and a corresponding architecture. First, we spilt the weight matrix into several small matrices by clustering adjacent columns together. Second, we extract 1s' patterns, i.e., the submatrices only containing 1s, from the small weight matrix, such that each final output can be represented by the sum of several patterns. Third, we map these patterns onto RRAM crossbars, including pattern computation crossbars (PCCs) and pattern accumulation crossbars (PACs). Finally, we compare the pattern representation with two mainstream representations and adopt the more area efficient one. The evaluation results demonstrate that our framework can save over 20% of crossbar area effectively, compared with two mainstream representations.

Key words: binary neural network (BNN); pattern; resistive random access memory (RRAM);