Compute-in-memory (CIM) accelerators for spiking neural networks (SNNs) are promising solutions to enable μs-level inference latency and ultra-low energy in edge vision applications. Yet, their current lack of flexibility at both the circuit and system levels prevents their deployment in a wide range of real-life scenarios. In this work, we propose FlexSpIM, a novel digital CIM macro that supports arbitrary operand resolution and shape within a unified CIM storage for weights and membrane potentials. These circuit-level techniques enable a hybrid weight- and output-stationary dataflow at the system level to maximize operand reuse, thereby minimizing costly on- and off-chip data movements during the SNN execution. Measurement results of a fabricated FlexSpIM prototype in 40-nm CMOS demonstrate a 2× increase in 1-bit-normalized energy efficiency compared to prior fixed-precision digital CIM-based SNNs, while providing resolution reconfiguration with bitwise granularity. Our approach can save up to 90% energy in large-scale systems, while reaching a state-of-the-art classification accuracy of 95.8% on the IBM DVS gesture dataset.

As artificial intelligence (AI) continues to transform multiple sectors, its exponential growth in computational demands presents significant challenges for hardware infrastructure. This article examines sparsity, the prevalence of zeros in AI workloads, as a promising approach to address these challenges. While sparsity offers potential efficiency gains, its practical implementation requires careful consideration of hardware constraints and computational overheads. Therefore, this article cooperates with a virtual performance roofline model to analyze various sparsity techniques and their associated tradeoffs, aiming to bridge the gap between theoretical potential and practical implementation in AI accelerator design.