CSIA-UIM: A Universal Ising Machine Based on CIM-friendly Spring-Ising Algorithm

Ising machines are specialized processors designed to solve combinatorial optimization problems through the physical evolution of the Ising graphs. However, conventional Ising machines are restricted to solving problems with specific graph topologies and are further hindered by the inherent memory wall of the von Neumann architecture. In this work, we propose a Computing-In-Memory-friendly Spring-Ising Algorithm (CSIA) to solve Ising models with arbitrary graph topologies. Building on CSIA, we introduce a universal Ising machine (CSIA-UIM) capable of fully parallel spin updates. The CSIA-UIM adopts a Time-Domain Computing-In-Memory architecture, with key modules including the Generalized Momentum Update Module (GMUM), Generalized Coordinate Update Module (GCUM), and Hardware Inelastic Wall (HIW) working collaboratively in a parallel pipeline fashion. Hybrid simulation results show that CSIA-UIM achieves speed improvements of 468×, 64×, 2.5×, compared to GPU, RRAM-based, and CMOS-based universal Ising machines, respectively, when solving a fully connected Ising model with 1,000 spins.