Design Space Exploration of a Mesochronous Link for Cost-Effective and Flexible GALS NOCs

There is today little doubt on the fact that a high-performance and cost-effective Network-on-Chip can only be designed in 45nm and beyond under a relaxed synchronization assumption. In this direction, this paper focuses on a GALS system where the NoC and its end-nodes have independent clocks (unrelated in frequency and phase) and are synchronized via dual-clock FIFOs at network interfaces. Within the network, we assume mesochronous synchronization implemented with hierarchical clock tree distribution. This paper contributes two essential components of any practical design automation support for network instantiation in the target system. On one hand, it introduces a switch design which greatly reduces the overhead for mesochronous synchronization and can be adapted to meet different layout constraints. On the other hand, the paper illustrates a design space exploration framework of mesochronous links that can direct the selection of synchronization options on a port-by-port basis for all the switches in the NoC, based on timing and layout constraints. A final case study illustrates how a cost-effective GALS NoC can be assembled, placed and routed by exploiting the flexibility of the architecture and the outcomes of the exploration framework, thus proving the viability and effectiveness of the design platform.