This paper introduces the concept of overloaded CSRU (Cyclic Shift Register with Accumulator) crossbars as a physical layer solution for Network-on-Chip (NoC) routers. The overloaded CSRU approach enhances channel capacity by utilizing nonorthogonal codes. Two crossbar architectures, namely T-OCI and P-OCI, are proposed to increase the CSRU crossbar capacity by 100% and 2N×100%, respectively, where N represents the length of the spreading code.

The paper leverages the properties of the Walsh spreading code family, commonly used in conventional CSRU crossbars, to enable a larger number of router ports to share the crossbar without modifying the simple accumulator decoder architecture of the traditional CSRU crossbar. The paper presents procedures for generating nonorthogonal spreading codes and describes the reference and pipelined architectures for each crossbar variant. Both T-OCI and P-OCI crossbars are implemented, and their performance is compared to that of the conventional CSRU crossbar.

The evaluation shows that the T-OCI crossbar achieves a 45% reduction in dynamic power consumption compared to the conventional CSRU crossbar, while the P-OCI crossbar experiences a 133% increase in dynamic power consumption. Furthermore, the T-OCI crossbar utilizes 31% fewer resources, whereas the P-OCI crossbar requires 400% more resources compared to the conventional CSRU crossbar.

To assess the suitability of OCI (Overloaded CSRU with Nonorthogonal Codes) crossbars for NoCs, the paper performs analytical and experimental evaluations on a fully operational OCI-based NoC. A 65-node OCI-based star NoC is implemented and compared to an SDMA-based torus NoC generated by CONNECT. The evaluation results clearly demonstrate the superiority of OCI-based NoCs in terms of area utilization and throughput.

In summary, this paper presents the concept of overloaded CSRU crossbars as a physical layer solution for NoC routers, introduces T-OCI and P-OCI crossbar architectures, and evaluates their performance against the conventional CSRU crossbar. The paper establishes the suitability of OCI-based NoCs through analytical and experimental evaluations, showcasing their advantages in area utilization and throughput.