Using Transmission Lines for Global On-Chip Communication

The growing number of cores in chip multiprocessors increases the importance of interconnection for overall system performance and energy efficiency. Compared to traditional distributed shared-memory architectures, chip-multiprocessors (CMPs) offer a different set of design constraints and opportunities. As a result, a conventional packet-relay multiprocessor interconnect architecture is a valid, but not necessarily optimal, design point. Worsening wire delays, energy-inefficient routers, and the decreased importance of in-field scalability, make the conventional packet-switched network-on-chip a less attractive option. An alternative solution uses well-engineered transmission lines as communication links. These transmission lines, along with simple, practical circuits using modern complementary metal-oxide-semiconductor technology, can provide low latency, low energy, high throughput channels which can be used as a shared-medium point-to-point link. The design of the transmission lines and transceiver circuits has important architectural impact. This paper includes a first-step design effort for these components, particularly when used for a globally shared-medium bus. For medium-scale CMPs, this interconnect backbone can eliminate the need for packet switching and provide energy, as well as performance benefits when compared to a conventional mesh interconnect. We will provide a design of such a system from the ground up, including design of the transmission lines, transceiver circuits, and a simple, yet effective, architectural design for a shared-medium interconnect, and show that such a design can be a compelling alternative to packet-switched networks for CMPs.