A comprehensive comparison between virtual cut-through and wormhole routers for cache coherent Network on-Chips

Abstract

A basic design aspect of cache coherent Networks-on-Chip (NoCs) is the flow control mechanism. Since the minimum buffer size of virtual cut-through (VCT) switching is larger than that of the wormhole one, the VCT switching is traditionally regarded as an inefficient NoC flow control type. Yet, the scaling of semiconductor technology shrinks the transistor size, and reduces the criticality of buffer amount for NoC designs; the VCT switching may becomes a promising NoC flow control candidate. This paper performs a comprehensive comparison between the VCT and wormhole switching. Based on detailed RTL-level implementations, we evaluate the hardware costs with both deterministic and adaptive routing. Compared with the wormhole switching, the VCT one shortens the critical path by up to 27%, and induces less area and power overheads. Furthermore, the allocator in VCT routers exhibits a better scalability in area overheads. Thus, the VCT router is an efficient NoC flow control type.