Network-on-Chip Energy-Efficient Design Techniques for Interconnects Suhail Basit

23/5/2003Suhail Basit2 NoC Micro-network Components (Resources) Interconnects (Switches) Differences from WAN Local proximity of components Less non-determinism Mesh Topology

23/5/2003Suhail Basit3 NoC Design Power consumption Voltage scaling helps Computation and storage energy Device scaling helps Communication energy Needs extra effort Netwrok traffic monitoring and control Clock speed of components according to available bandwidth Design-time specialization Designing of communication network fabric on silicon from scratch Standardization of end nodes only Tailored netwrok architecture according to the application

23/5/2003Suhail Basit4 Interconnect Design Implementation of micro-network stack Physical layer Data transfer Synchronization Data-link layer Error handling Network layer Network architecture Network control Transport layer Network resources QoS System layer Power management Application Layer Distributivity Portability

23/5/2003Suhail Basit5 Physical Layer Design Low swing signaling at transmitter Reduction in V dd Less reliable data reception Differential receivers Pseudo-differential signaling at receiver Reference signal sharing Less signal transitions Reduced noise margin Synchronization Clocks are extremely energy-inefficient Global synchronization is not optimal GALS units are a possible solution

23/5/2003Suhail Basit6 Data-link Layer Design Error detection Retransmission of data in case of error Can be costly in energy and performance Error correction More redundant and complex in decoding More power-hungry in error-free case Optimal choice System constraints Physical channel characteristics

23/5/2003Suhail Basit7 Network Layer Design Hierarchical and heterogeneous architecture Nodes with high bandwidth requirement are clustered and connected together through short channels Clusters are connected through global channels Small energy cost of intera-cluster communication than inter-cluster communication Circuit switching Network control overhead incurrs only once Best in case of persistent communication Packet switching Distributed network control overhead More energy-efficient for irregular communication

23/5/2003Suhail Basit8 Transport Layer Design Connection-oriented protocol Energy inefficient under heavy traffic due to retransmissions Connection-less protocol Additional work at receiver due to out-of-order delivery of data Flow control Network congestion increases cost per transmitted bit due to contention resolution overhead The amount of data that enters the network, can be regulated, at the price of throughput

23/5/2003Suhail Basit9 System Layer Design Node-centric power management System software of each component has its own dynamic power management (DPM) policy Component changes state based on system state and workload (obtained by system calls) Network-centric power management Components request neighbors for a state change Requests originate and are serviced at system software level

23/5/2003Suhail Basit10 Application Layer Design Distributivity and Portability Power-aware application programming interfaces (APIs) for communication between application and system software Information about platform Setting the component in specific power state

23/5/2003Suhail Basit11 Conclusion Challenges of upcoming technologies Design complexity Reliable and high performance operation Energy consumption Interconnects are the limiting factor Energy-efficient and communication-centric designs Some problems were presented Basic strategies have been outlined Need to be explored further