CREAM: Computing in ReRAM-Assisted Energy- and Area-Efficient SRAM for Reliable Neural Network Acceleration

Abstract

SRAM-based computing-in-memory (CIM) has been widely explored to accelerate neural networks (NNs). However, it is challenging to store all weights of many modern NNs due to limited on-chip SRAM capacity. This bottleneck induces a large amount of off-chip DRAM accesses and impedes the improvement of performance and energy efficiency. This paper proposes a new approach of computing in resistive random-access memory (ReRAM)-assisted energy-and area-efficient SRAM (CREAM) for accelerating large-scale NNs while eliminating the DRAM access. The NN weights are all stored in high-density on-chip ReRAMs and restored to the proposed non-volatile SRAM (nvSRAM) CIM cells with array-level parallelism. Furthermore, to deal with the influence of ReRAM and CMOS variations, a novel layer-wise and bit-wise weight-configuration search algorithm is proposed by leveraging different sensitivity of each layer in NN models. A data-aware weight-mapping method is also presented to efficiently map NN models to ReRAMs in CREAM for high computation parallelism. The experiment results show 10.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> weight storage density over the standard 6T SRAM array. Evaluations of ResNet-18 and VGG-9 on CIFAR-10/CIFAR-100 datasets show up to 3.47 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> and 1.70 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> energy efficiency over two baseline designs of SRAM-CIM and ReRAM-CIM, respectively, in addition to 15.6% higher accuracy than ReRAM-CIM under device variations.