Overloaded CDMA bus topology for MPSoC interconnect

Abstract

Intra-chip communication is a major bottleneck in modern multiprocessor system-on-chip (MPSoC) designs. The bus topology is the most common on-chip interconnect technology and bus contention in one of the major issues in bus-based MPSoC designs. Code division multiple access (CDMA) has been proposed as a bus sharing strategy to overcome the bus contention problem. In CDMA, a limited number of orthogonal spreading codes can share the medium due to the Multiple Access Interference (MAI) problem. In wireless communications, overloaded CDMA has been considered to increase the system capacity by adding extra non-orthogonal spreading codes with specific characteristics. We propose a novel CDMA bus architecture leveraging the overloaded CDMA concepts to increase the maximum number of cores sharing the same CDMA bus in MPSoC by 25% at a marginal cost. The overloaded CDMA bus architecture is illustrated, resource- and speed-efficient decoding circuits are presented, and a prototype system is implemented and validated on a Virtex-7 FPGA VC707 evaluation kit. The overloaded and ordinary CDMA bus architectures are compared in terms of resource usage, power consumption, bus operating clock frequency and bandwidth. Evaluation results show an improvement in resource utilization and power consumption per unit (IP core) and the bus bandwidth by approximately %25 while preserving the access delay of the ordinary CDMA bus.