On-chip networks: A scalable, communication-centric embedded system design paradigm

As chip complexity grows, design productivity boost is expected from reuse of large parts and blocks of previous designs with the design effort largely invested into the new parts. More and more processor cores and large, reusable components are being integrated on a single silicon die but reuse of the communication infrastructure has been difficult. Buses and point to point connections, that have been the main means to connect components on a chip today, will not result in a scalable platform architecture for the billion transistor chip era. Buses can cost efficiently connect a few tens of components. Point to point connections between communication partners is practical for even fewer components. As more and more components are integrated on a single silicon die, performance bottlenecks of long, global wires preclude reuse of buses. Therefore, scalable on-chip communication infrastructure is playing an increasingly dominant role in system-on-chip designs. With the super-abundance of cheap, function-specific IP cores, design effort will focus on the weakest link: efficient on-chip communication. Future on-chip communication infrastructure will overcome the limits of bus-based systems by providing higher bandwidth, higher flexibility and by solving the clock skew problem on large chips. It may, however present new problems: higher power consumption of the communication infrastructure and harder-to-predict performance patterns. Solutions to these problems may result in a complete overhaul of SOC design methodologies into a communication-centric design style. The envisioning of upcoming problems and possible benefits has led to intensified research in the field of what is called NoCs: Networks on Chips. The term NoCs is used in a broad meaning, encompassing the hardware communication infrastructure, the middleware and operating system communication services, and a design methodology and tools to map applications onto a network on chip. This paper discusses trends in system-on-chip designs, critiques problems and opportunities of the NoC paradigm, summarizes research activities, and outlines several directions for future research.