Architectural exploration and performance analysis of Vertically-Partially-Connected Mesh-based 3D-NoC

Overview & Synopsis

Utilization of the third dimension can lead to a significant reduction in power and average hop-count in Networks- on-Chip (NoC). TSV technology, as the most promising technology in 3D integration, offers short and fast vertical links which copes with the long wire problem in 2D NoCs. Nonetheless, TSVs are huge and their manufacturing process is still immature, which reduces the yield of 3D NoC based SoC. Therefore, Vertically-Partially-Connected 3D-NoC has been introduced to benefit from both 3D technology and high yield. Moreover, Vertically-Partially-Connected 3D-NoC is flexible, due to the fact that the number, placement, and assignment of the vertical links in each layer can be decided based on the limitations and requirements of the design. However, there are challenges to present a feasible and high-performance Vertically-Partially-Connected Mesh-based 3D-NoC due to the removed vertical links between the layers. This thesis addresses the challenges of Vertically-Partially-Connected Mesh-based 3D-NoC: Routing is the major problem of the Vertically-Partially-Connected 3D-NoC. Since some vertical links are removed, some of the routers do not have up or/and down ports. Therefore, there should be a path to send a packet to upper or lower layer which obviously has to be determined by a routing algorithm. The suggested paths should not cause deadlock through the network. To cope with this problem we explain and evaluate a deadlock- and livelock-free routing algorithm called Elevator First. Fundamentally, the NoC performance is affected by both 1) micro-architecture of routers and 2) architecture of interconnection. The router architecture has a significant effect on the performance of NoC, as it is a part of transportation delay. Therefore, the simplicity and efficiency of the design of NoC router micro architecture are the critical issues, especially in Vertically-Partially-Connected 3D-NoC which has already suffered from high average latency due to some removed vertical links. Therefore, we present the design and implementation the micro-architecture of a router which not only exactly and quickly transfers the packets based on the Elevator First routing algorithm, but it also consumes a reasonable amount of area and power. From the architecture point of view, the number and placement of vertical links have a key role in the performance of the Vertically-Partially-Connected Mesh-based 3D-NoC, since they affect the average hop-count and link and buffer utilization in the network. Furthermore, the assignment of the vertical links to the routers which do not have up or/and down port(s) is an important issue which influences the performance of the 3D routers. Therefore, the architectural exploration of Vertically-Partially-Connected Mesh-based 3D-NoC is both important and non-trivial. We define, study, and evaluate the parameters which describe the behavior of the network. The parameters can be helpful to place and assign the vertical links in the layers effectively. Finally, we propose a quadratic-based estimation method to anticipate the saturation threshold of the network's average latency.