Overloaded CDMA Crossbar for Network-On-Chip

Abstract

On-chip interconnects are the performance bottleneck in modern system-on-chips. Code-division multiple access (CDMA) has been proposed to implement on-chip crossbars due to its fixed latency, reduced arbitration overhead, and higher bandwidth. In CDMA, medium sharing is enabled in the code space by assigning a limited number of ${N}$ -chip length orthogonal spreading codes to the processing elements sharing the interconnect. In this paper, we advance overloaded CDMA interconnect (OCI) to enhance the capacity of CDMA network-on-chip (NoC) crossbars by increasing the number of usable spreading codes. Serial and parallel OCI architecture variants are presented to adhere to different area, delay, and power requirements. Compared with the conventional CDMA crossbar, on a Xilinx Artix-7 AC701 FPGA kit, the serial OCI crossbar achieves 100% higher bandwidth, 31% less resource utilization, and 45% power saving, while the parallel OCI crossbar achieves ${N}$ times higher bandwidth compared with the serial OCI crossbar at the expense of increased area and power consumption. A 65-node OCI-based star NoC is implemented, evaluated, and compared with an equivalent space division multiple access based torus NoC for various synthetic traffic patterns. The evaluation results in terms of the resource utilization and throughput highlight the OCI as a promising technology to implement the physical layer of NoC routers.