SC-CGRA: An Energy-Efficient CGRA Using Stochastic Computing

Stochastic Computing (SC) offers a promising computing paradigm for low-power and cost-effective applications, with the added advantage of high error tolerance. In parallel, Coarse-Grained Reconfigurable Arrays (CGRA) prove to be a highly promising platform for domain-specific applications due to their combination of energy efficiency and flexibility. Intuitively, introducing SC to CGRA would significantly reinforce the strengths of both paradigms. However, existing SC-based architectures often encounter inherent computation errors, while the stochastic number generators employed in SC result in exponentially growing latency, which is deemed unacceptable in CGRA. In this work, we propose an SC-based CGRA by replacing the exact multiplication in traditional CGRA with an SC-based multiplication. To improve the accuracy of SC and shorten the latency of Stochastic Number Generators (SNG), we introduce the leading zero shifting and comparator truncation, while keeping the length of bitstream fixed. In addition, due to the flexible interconnections among PEs, we propose a quality scaling strategy that combines neighbor PEs to achieve high-accuracy operations without switching costs like power-gating. Compared to the state-of-the-art approximate computing design of CGRA, our proposed CGRA can averagely achieve a 65.3% reduction in output error while having a 21.2% reduction in energy consumption and a noteworthy 28.37% area savings.