Efficient SRAM-PIM Co-Design by Joint Exploration of Value-Level and Bit-Level Sparsity

Processing-in-memory (PIM) architectures mitigate the Von Neumann bottleneck by integrating computation units into memory arrays. Among PIM architectures, digital SRAMPIM has become a prominent approach, directly integrating digital logic within the SRAM array. However, the rigid crossbar architecture and full array activation pose challenges in efficiently utilizing value-level sparsity. Moreover, neural network models exhibit a high proportion of zero bits within non-zero values, which remain underutilized due to architectural constraints. To overcome these limitations, we present Dyadic Block PIM (DB-PIM), a groundbreaking algorithm-architecture co-design framework to harness both value-level and bit-level sparsity. At the algorithm level, our hybrid-grained pruning technique, combined with a novel sparsity pattern, enables effective sparsity management. Architecturally, DB-PIM incorporates a sparse network and customized digital SRAM-PIM macros, including input pre-processing unit (IPU), dyadic block multiply units (DBMUs), and Canonical Signed Digit (CSD)-based adder trees. It circumvents structured zero values in weights and bypasses unstructured zero bits within non-zero weights and block-wise all-zero bit columns in input features. As a result, the DBPIM framework skips a majority of unnecessary computations, thereby driving significant gains in computational efficiency. Experimental results demonstrate that our DB-PIM framework achieves up to 8.01× speedup and 85.28% energy savings, significantly boosting computational efficiency in digital SRAMPIM systems.