Synthesis of Compact Flow-based Computing Circuits from Boolean Expressions

Processing in-memory has the potential to accelerate high-data-rate applications beyond the limits of modern hardware. Flow-based computing is a computing paradigm for executing Boolean logic within nanoscale memory arrays by leveraging the natural flow of electric current. Previous approaches of mapping Boolean logic onto flow-based computing circuits have been constrained by their reliance on binary decision diagrams (BDDs), which translates into high area overhead. In this paper, we introduce a novel framework called FACTOR for mapping logic functions into dense flow-based computing circuits. The proposed methodology introduces Boolean connectivity graphs (BCGs) as a more versatile representation, capable of producing smaller crossbar circuits. The framework constructs concise BCGs using factorization and expression trees. Next, the BCGs are modified to be amenable for mapping to crossbar hardware. We also propose a time multiplexing strategy for sharing hardware between different Boolean functions. Compared with the state-of-the-art approach, the experimental evaluation using 14 circuits demonstrates that FACTOR reduces area, speed, and energy with 80%, 2%, and 12%, respectively, compared with the state-of-the-art synthesis method for flow-based computing.