Network-on-Chip An Overview System-on-Chip Group, CSE-IMM, DTU

© System-on-Chip Group, CSE-IMM, DTU 2 Introduction – intra chip communication PP Keypad Network DSP Memory RF

© System-on-Chip Group, CSE-IMM, DTU 3 Introduction – intra chip communication PP Keypad DSP Memory RF BUS

© System-on-Chip Group, CSE-IMM, DTU 4 Introduction – intra chip communication PP Keypad DSP Memory RF Point-to-Point

© System-on-Chip Group, CSE-IMM, DTU 5 Overview Important Paradigms Network Abstraction Performance Evaluation Research Opportunities

© System-on-Chip Group, CSE-IMM, DTU 6 Important Paradigms for NoC Re-use Flexibility GALS Low Power Core Network Adapter Routing Node Link

© System-on-Chip Group, CSE-IMM, DTU 7 On-Chip vs Off-Chip On-Chip Cheap Wires Power Limited Area Limited Unreliable Wire Models Off-Chip Wire/pin Limited High Latency Higher Node Complexity Viable

© System-on-Chip Group, CSE-IMM, DTU 8 µPµP Mem. Typical P2P Write Session (3 comm. events) DATA ACK µPµPNI “Networked” Write Session (4 comm. event) DATA N-ACK Mem. NI DATA WRT Network Usage Example

© System-on-Chip Group, CSE-IMM, DTU 9 Network Abstraction - OSI Application/ Presentation Layers Session/ Transport Layer Network, Link and Physical Layers Socket Sink Core Source Core Network Interface Core Interface

© System-on-Chip Group, CSE-IMM, DTU 10 Network Dataflow View Socket Sink Core Source Core Packets Flit Phif Messages

© System-on-Chip Group, CSE-IMM, DTU 11 Memory Application Layer Traffic Characterization µP, Dedicated Hardware Communication Msg. Size smalllarge Freq. of Comm. Events high low I/O (sensors, wired/wireless) DSP, Application Specific Blocks

© System-on-Chip Group, CSE-IMM, DTU 12 Application Based Communication Network Design The consistent theme in the literature is to design on-chip network for the application the chip is utilized for, but there is a growing integration of various application cores within a single chip. Hence the need for the network to be flexible and robust so that it can support diverse types and volume of traffic generated by different cores. An example is the Nokia’s future mobile set that can provide real-time application needs as well as “low latency” data needs.

© System-on-Chip Group, CSE-IMM, DTU 13 QoS lowhigh Bandwidth Utilization Traffic Distribution low high ‘Normal’ (bulk) traffic Critica l events Control, interrupts, requests, et al? Streaming

© System-on-Chip Group, CSE-IMM, DTU 14 Network Abstraction Session / Transport Layer Plug and play interface Traffic encapsulation Network / Link Layer Topology Protocol

© System-on-Chip Group, CSE-IMM, DTU 15 Network Abstraction Physical Layer Sub-micron technologies pose challenges Circuit design  Low-swing drivers  Differential signaling  Asynchronous Link implementations such as virtual circuits

© System-on-Chip Group, CSE-IMM, DTU 16 Networks-on-Chip Many combinations! How to judge trade-offs?!

© System-on-Chip Group, CSE-IMM, DTU 17 Boil Down of OSI Presentation Application Transport Network Session Data Physical OSINoCJob Description Application Message Source/Sink Interface Network Configuration Error Correction Packet Creation, Message Reconstruction Addressing Network Flow Control Prioritization (Bandwidth Reservation) Link Point-to-point Channels (wires)

© System-on-Chip Group, CSE-IMM, DTU 18 Performance Evaluation Quantitative terms Latency Bandwidth Power Area Qualitative terms QoS Load balancing Reconfigurability Fault tolerance … more features?

© System-on-Chip Group, CSE-IMM, DTU 19 Tools and Testing NoC is a subset of SoC Tools  Design  Simulation Testing  Pre-fabrication  Post-fabrication

© System-on-Chip Group, CSE-IMM, DTU 20 Issues At Application Layer Minimizing the end-to-end latency Making network communication “transparent” Support for different traffic types At Interface Layer Message-to-packet overhead (and vice versa) Breaking up and re-sequencing? Error Correction cost? Addressing techniques? End-to-end flow control Message buffer sizing? Circuit-switching-like properties? QoS (Network setup cost, BW reservation)?

© System-on-Chip Group, CSE-IMM, DTU 21 Issues, cont… At Network Layer Need specialized technique for “fast and dedicated routing” Combination of deterministic and non-deterministic routing? Topology Link-to-link Flow Control Packet buffer sizing? Virtual channels (deadlock avoidance)? Back pressure (Congestion look-ahead)? Routing Mechanism Address resolution Bandwidth reservation At Link Layer Fast flexible links Virtual channels? Split channels for multi-flit-per-cycle communication? Dedicated Address / Control lines?

© System-on-Chip Group, CSE-IMM, DTU 22 Overhead Considerations Routing Protocol Congestion control Error-correction Network setup/tear-down Synchronization

© System-on-Chip Group, CSE-IMM, DTU 23 Research Opportunities Traffic + Application Topology + Protocol Reconfigurability Area + Power Issues Interfaces (GALS) Sub-micron Technology Exploitation

© System-on-Chip Group, CSE-IMM, DTU 24 References BJERREGAARD, T. and MAHADEVAN, S “NoC Survey Manuscript”, Submitted. HO, R.,MAI, K. W., AND HOROWITZ,M. A The future of wires. Proceedings of the IEEE. ITRS International technology roadmap for semiconductors (ITRS) Tech. rep., International Technology Roadmap for Semiconductors. JANTSCH, A. AND TENHUNEN, H Networks on Chip. Kluwer Academic Publishers. LEE, K On-chip interconnects - gigahertz and beyond. Solid State Technology. OCPIP. The importance of sockets in soc design. White paper downloadable from BENINI, L. AND MICHELI, G. D Networks on chips: A new soc paradigm. IEEE Computer. DALLY, W. J. AND TOWLES, B Route packets, not wires: On-chip interconnection networks. In Proceedings of the 38th Design Automation Conference. DIELISSEN, J., RADULESCU, A., GOOSSENS, K., AND RIJPKEMA, E Concepts and implementation of the phillips network-on-chip. In Proceedings of the IP based SOC IPSOC’03. GOOSSENS,K.,MEERBERGEN, J. V., PEETERS, A., AND WIELAGE, P Networks on silicon: Combining best-effort and guaranteed services. In Proceedings of the 2002 Design, Automation and Test in Europe Conference (DATE’02). IEEE.