Advanced Processor Group

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A Dynamic Link Allocation Router

• Wei Song, Doug Edwards
• Advanced Processor Group
• The University of Manchester

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Overview

• Network-on-a-Reconfigurable-Chip
• The Dynamic Link Allocation Flow control method
• The Dynamic Link Allocation Router (DyLAR)
• Conclusion

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The NoRC Platform

• NoRC network on a reconfigurable chip
• Running multimedia applications
• Connection oriented
• Stochastic routing algorithm
• GALS fully asynchronous routers linked by CHAIN

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Connection Oriented Routing

• Flit Definitions

Request Flit
Other Flits
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The High Retry Rate
Simulation results of a 6x6 NoC with 12 functions
in network.
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Virtual Channels are required to reduce the retry
rate.
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Overview

• Network-on-a-Reconfigurable-Chip
• The Dynamic Link Allocation Flow control method
• The Dynamic Link Allocation Router (DyLAR)
• Conclusion

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Major Design Targets

• Implement some kind of virtual channels
• Increase the bandwidth of CHAIN links
• Reduce the area and power of the router

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Increase the bandwidth
Asynchronous Links work better with the lower
wire count.
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Increase the bandwidth
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Increase the bandwidth
Spatial division multiplex (SDM) is a good choice
for asynchronous NoCs.
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Problems of SDM
Spare sub-link
SDM has the low bandwidth efficiency.
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Problems of SDM
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Dynamic Link Allocation

• Divide the sub-link allocation apart from the
  path reservation
• Allocate idle sub-link to active communications
  that reserved this link
• All communications fairly compete for the
  bandwidth

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Overview

• Network-on-a-Reconfigurable-Chip
• The Dynamic Link Allocation Flow control method
• The Dynamic Link Allocation Router (DyLAR)
• Conclusion

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Dynamic Link Allocation Router (DyLAR)
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Path Reservation Stage
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Data Transmission Stage
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Head-of-line (HOL) Problem
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Backpressure
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Backpressure
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Overview

• Network-on-a-Reconfigurable-Chip
• The Dynamic Link Allocation Flow control method
• The Dynamic Link Allocation Router (DyLAR)
• Conclusion

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Conclusion

• Contribution
• A new flow control method
• Implement the first asynchronous spatial division
  router
• Advantages
• Smaller latency under zero load
• Larger overall throughput under heavy load
• Smaller retry rate (smaller power consumption)
• Problems
• An extra request switch in each router
• Extra control logic
• Increase the latency to pass a router

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Thank You!

• Questions?

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Detailed Procedures

• Request
• Path reserved
• Sending data
• Release path

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Request Procedure
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Request Procedure
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Request Procedure
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Request Procedure
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Request Procedure
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Request Procedure
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OK Ack
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Data Flits
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Data Flits
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Data Flits
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Data Flits
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Data Flits
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Data Flits
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Data Flits
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False Ack
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False Ack