Network-on-Chip

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

2. NoC • Micro-network • Components (Resources) • Interconnects (Switches) • Differences from WAN • Local proximity of components • Less non-determinism Mesh Topology Suhail Basit

3. 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 Suhail Basit

4. 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 Suhail Basit

5. Physical Layer Design • Low swing signaling at transmitter • Reduction in Vdd • 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 Suhail Basit

6. 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 Suhail Basit

7. 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 Suhail Basit

8. 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 Suhail Basit

9. 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 Suhail Basit

10. 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 Suhail Basit

11. 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 Suhail Basit