A vertical bubble flow network using inductive-coupling for 3-D CMPs

A wireless 3-D NoC architecture for CMPs, in which the number of processor and cache chips stacked in a package can be changed after the chip fabrication, is proposed by using the inductive coupling technology that can connect more than two known-good-dies without wire connections. Each chip has data transceivers for uplink and downlink in order to communicate with its neighboring chips in the package. These chips form a single vertical ring network so as to fully exploit the flexibility of the wireless approach that enables us to add, remove, and swap the chips in the ring. To avoid protocol and structural deadlocks in the ring network, we use the bubble flow control which is more flexible and efficient compared to the conventional VC-based deadlock avoidance. We implemented a real 3-D chip that has on-chip routers and inductive-coupling data transceivers using a 65nm process in order to show the feasibility of our proposal. The vertical bubble flow control is compared with the conventional VC-based approach and vertical bus in terms of the throughput, hardware amount, and application performance using a full system CMP simulator. The results show that the proposed vertical bubble flow network outperforms the VC-based approach by 7.9%-12.5% with a 33.5% smaller router area.