Enhanced Overloaded CDMA Interconnect (OCI) Bus Architecture for On-Chip Communication

On-chip interconnect is a major building block and a main performance bottleneck in modern complex System-on-Chips (SoCs). The bus topology and its derivatives are the most deployed communication architectures in contemporary SoCs. Space switching exemplified by cross bars and multiplexers, and time sharing are the key enablers of various bus architectures. The cross bar has quadratic complexity while resource sharing significantly degrades the overall system´s performance. In this work we motivate using Code Division Multiple Access (CDMA) as a bus sharing strategy which offers many advantages over other topologies. Our work seeks to complement the conventional CDMA bus features by applying overloaded CDMA practices to increase the bus utilization efficiency. We propose the Difference-Overloaded CDMA Interconnect (D-OCI) bus that leverages the balancing property of the Walsh codes to increase the number of interconnected elements by 50%. Two implementations of the D-OCI bus optimized for both speed and resource utilization are presented. The bus operation is validated on a Xilinx Artix-7 AC701 FPGA kit and the bus performance is evaluated and compared to other existing bus topologies. We also present the synthesis results for the UMC-0.13 μm design kit to give an idea of the maximum achievable bus frequency on ASIC platforms. Moreover, we advance a proof-of-concept HLS implementation of the D-OCI bus on a Xilinx Zynq-7000 SoC and compare its performance, latency, and resource utilization to the ARM AXI bus. The performance evaluation demonstrates the superiority of the D-OCI bus.