Networks-on-Chip

Chapter 7

Deadlock-free flow control for torus networks-on-chip^†

Abstract

Short and long packets coexist in cache-coherent networks-on-chip. Existing designs for torus networks do not efficiently handle variable-size packets. For deadlock-free operations, a design uses two virtual channels (VCs), which negatively affects the router frequency. Some optimizations use one VC. Yet, they regard all packets as maximum-length packets, inefficiently utilizing the precious buffers. We propose flit bubble flow control (FBFC), which maintains one free flit-size buffer slot to avoid deadlock. FBFC uses one VC, and does not treat short packets as long ones. It achieves both high frequency and efficient buffer utilization. FBFC performs 92.8% and 34.2% ...