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On-Chip Photonic
Nima AfrazKazem farjami nejhad
For the Advanced VLSI Course Term Paper Presentation
February 20121
Why? To improve performance and energy in a future
many-core processor, it is vital that the interconnect technology is optimized.
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Optical networks silicon photonics is a promising new interconnect
technology with lower power, higher bandwidth density, and shorter latencies.
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Contents Introduction Architecture Overview Analysis and Comparison Conclusion
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IntroductionLow-latency high-bandwidth: How? Packet-switched networks
Made of carefully engineered links Represent a shared medium that is highly scalable Provide enough bandwidth
But... Communication infrastructure is the major power
consumer Power dissipation budget limit will be achieved
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IntroductionPhotonic Technology Photonic interconnection networks
Low power dissipation independent of capacity Ultra-high throughput Minimal access latencies
Why less power? Once a photonic path is established, the data is
transmitted end to end without the need for repeating, regeneration and buffering
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IntroductionPhotonic Technology Is photonic technology cheap enough?
Since 2006, high-speed optical communications directly between silicon die are possible at a price-performance point competitive with traditional electrical interconnects
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Contents Introduction Architecture Overview Analysis and Comparison Conclusion
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Architecture Overview Phonotonic NoC Hybrid Approach
Photonic interconnection network Transmits high-bandwidth messages
Electronic control network Controls the photonic network with small control messages
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Architecture OverviewPhonotonic NoC Before transmitting a photonic message, an
electronic control packet (path-setup packet) is routed in the electronic network acquires and sets up a photonic path for the
message Photonic message is transmitted without
buffering once the path is acquired
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Architecture OverviewPhotonic NoC Main advantage of photonic paths is bit-rate
transparency Photonic switches switch on or off once per
message Energy dissipation does not depend on the bit-rate
whereas Traditional CMOS routers switch with every bit of
transmitted data
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Architecture OverviewPhotonic NoC Another advantage is low loss in optical
waveguides Power dissipated on a photonic link is completely
independent of the transmission distance No matter if 2 cores are 2mm or 2cm apart
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Architecture OverviewPhotonic NoC 2X2 photonic switching elements
Capable of switching messages in a sub nanosecond switching time
Switches are arranged as a 2D matrix and organized in groups of four Each group is controlled by an electronic router to
construct a 4X4 switch Convenient for planar 2D topologies such as mesh
and torus
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Architecture OverviewPhotonic NoC Each node includes a network gateway to serve as
a photonic network interface Electronic/Optical (E/O) and Optical/Electronic (O/E)
conversions Clock synchronization and recovery Serialization/deserialization
Wavelength division multiplexing is used at network gateways to provide larger data capacity Optical equivalent of using parallel wires
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Architecture OverviewLife of a Packet on Photonic NoC Write operation from a processor in Node A to a memory in
Node B1. A path-setup packet is sent on the electronic control
network Includes information on the destination address of Node B
and additional control information such as priority and flow id
2. Path-setup packet is routed in the electronic control network Reserves the photonic switches along the path At every router in the path, the next hop is decided
according to the routing algorithm used3. Path-setup packet reaches the destination
Photonic path is reserved A fast light pulse is sent on the photonic path from Node B
to Node A to indicate that the path is reserved
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Architecture OverviewLife of a Packet on Photonic NoC
4. The photonic message starts from Node A follows path from switch to switch until it reaches Node B
5. Message transmission completed6. Path-teardown packet is sent from Node B to
Node A on the electronic control network to release the path
7. Photonic message is checked for errors and a small acknowledgement packet is sent from Node B to Node A on the electronic control network
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Contents Introduction Architecture Overview Analysis and Comparison Conclusion
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Analysis and ComparisonPower Dissipation Case Study Setup
16-node CMP where each processor requires BWpeak = 1024 Gb/s BWavg = 800 Gb/s
Traffic driven by the processors is assumed to be uniform
Both networks use a mesh topology and XY dimension order routing
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Analysis and ComparisonPower Dissipation Reference Electronic Network
4X4 mesh, where each router is integrated in one processor tile
PW=765W Photonic Network
8X8 photonic mesh 256 photonic switching elements organized as 64
4X4 switches PW=30W (96% less power dissipation)
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Contents Introduction Architecture Overview Analysis and Comparison Conclusion
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Conclusion The advantages of photonic medium
High transmission bandwidth Low power consumption
Recent (i.e. since 2006) advances make photonic technology practical for NoCs Fabrication of silicon photonic devices Integration of photonic devices in CMOS electronic
circuits Next generation of NoCs will possibly use
photonic technology
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References On the Design of a Photonic Network-on-Chip
Assaf Shacham, Keren Bergman, Luca P. Carloni First International Symposium on Networks-on-Chip (NOCS'07), pp. 53-64,
2007 Photonic Networks-on-Chip: Opportunities and Challenges
Michele Petracca, Keren Bergman, Luca P. Carloni IEEE International Symposium on Circuits and Systems 2008 (ISCAS 2008),
pp. 2789-2792, May 2008 The Case for Low-Power Photonic Networks on Chip
Assaf Shacham, Keren Bergman, Luca P. Carloni Proceedings of the 44th Annual Conference on Design Automation, pp. 132-
135, 2007 Maximizing GFLOPS-per-Watt: High-Bandwidth, Low Power Photonic
On-Chip Networks Shacham, K Bergman, LP Carloni IBM P=ac2 Conference, October 2006
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