1 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 LDM Link Division Multiplexing Arkadiy Morgenshtein, Avinoam Kolodny, Ran Ginosar Technion – Israel Institute of Technology MATRICS Research Group, Electrical Engineering Department Technion – Israel Institute of Technology Haifa, Israel MATRICS Research Group

2 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Background & Motivation

3 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Networks-on-Chip (NoC) NoC Characteristics Packets-based data routing Modules connected by routers network Shared links Supports QoS communication - QNoC

4 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Quality of Service in NoC QNoC – NoC with QoS Signaling – urgent short packets Read-Time – audio/video applications Read/Write – memory and register access Block-Transfer – long blocks of data low latency, high priority latency ↑, priority ↓ latency ↑ ↑, priority ↓ ↓ high latency, low priority

5 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Motivation tt Data is transmitted using Time-Sharing At each time slot all the wires are dedicated to a single source QoS priority defines order and duration for each source - Low link utilization - Timing dependency - High power solution Link Division Multiplexing (LDM) Data flow in QNoC links

6 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 LDM Concept

7 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 multi-serial LDM m X m-to-n serializers m-parallel Time Sharing m Link Division Multiplexing (LDM) Link resources (wires) are divided among QoS levels – Link Division Multiplexing The link is composed of outputs of several serializers Each serializer is dedicated to transmission of data at certain QoS level The number of wires at each level is allocated according to QoS level priority. LDM allows simultaneous transport of data in various QoS levels. m-to-1 serial Time Sharing

8 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 LDM allows dynamic division of resources according to QoS levels + Full utilization of the link resources + No timing dependency of lower QoS levels on higher levels + Simultaneous data transport at different QoS levels while maintaining the throughput and latency demands + Higher data transmission rate with improved efficiency of power control Link Division Multiplexing (LDM) X m-to-n serializers m

9 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 LDM Architecture

10 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 LDM Transceiver

11 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Controller Implementation Trade-offs + Reduced wiring overhead - Reduced data efficiency rate Add the control data to the packet. Each wire carries the information about the packet to which it is designated. + Reduced hardware overhead - Reduced flexibility and utilization Predefined allocation patterns of wires. Wires allocated according to operation mode without control communication. + High data efficiency rate & flexibility - Increased wiring overhead Send control signals at dedicated wires. Additional wires used for control communication in the transceiver. Alternative our architecture

12 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 QNoC Router with LDM Link TDMLDM TDM – data is classified and stored in dedicated buffers according to QoS levels LDM – various QoS levels are treated simultaneously, no need for separate storage + Fewer buffers are needed in LDM

13 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Results

14 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Simulation Setup LDM communication environment was implemented and emulated in Matlab QNoC link with 32 wires connected between two routers with four clients each Two possible patterns of wires allocation were set: {8,8,8,8} {16,8,4,4} Four QoS levels were used – Signaling, Real-Time, R/W, Block-Transfer Parameters were defined for each QoS level: Size of packet (in 32-bit flits) Probability of data appearance at given QoS level (including “no data”) Delay expressing the processing time of packet before transmission For each client a profile was built basing on set of five data probabilities

15 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 LDM in Various Data Scenarios Simulations contained data generation and transport during 100,000 clock cycles The simulation scenarios were divided into two types: Homogeneous – same QoS probability profiles for all clients Heterogeneous – different QoS probability profiles for all clients Number of transported flits in LDM was increased by up to 40% Flits transmittedQoS probability Clientscenariodistribution type TDMLDMP block-trans P read/write P real-time P signaling P no-data allA homogeneous allB C1C1 C heterogeneous C2C C3C C4C C1C1 D C2C C3C C4C4

16 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Performance vs. Packet Delays TDM LDM LDM effectiveness was evaluated as function of packets delay before transmission. Number of transported flits in LDM was increased by up to 50% LDM link has maximum value for certain delay. for low delays there is a queue of data in the buffer for higher delays the number of the flits reduces similarly to TDM.

17 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 LDM with lower V DD X m-to-n serializers TDM Power Reduction in LDM High link utilization in LDM Longer sleep mode allowed in LDM – clock and supply gating Timing can be traded for Voltage Scaling to reduce power LDM T TDM X m-to-n serializers T LDM or T LDM_low T TDM = T LDM + T sleep V TDM = V LDM sleep T TDM = T LDM_low V TDM > V LDM_low P LDM < P TDM

18 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Summary Link Division Multiplexing proposed LDM targets improvement of link utilization Increase in data rate and reduction of power LDM link was implemented and simulated Number of transmitted flits increased by up to 50%

19 Link Division Multiplexing (LDM) for NoC Links IEEE 2006 Questions? m-to-1 n m X m-to-n serializers