Electrical and Computer Engineering UAH System Level Optical Interconnect Optical Fiber Computer...
-
Upload
keila-hendley -
Category
Documents
-
view
215 -
download
0
Transcript of Electrical and Computer Engineering UAH System Level Optical Interconnect Optical Fiber Computer...
Electrical and Computer Engineering
UAHSystem Level Optical Interconnect
Optical Fiber Computer Interconnect:The Simultaneous Multiprocessor
Exchange (SOME)-Bus
Rhonda Kay Gaede
The University of Alabama in HuntsvilleDepartment of Electrical and Computer Engineering
Huntsville, AL 35899
UAHOptical Interconnects for High Performance System Level Optical InterconnectComputing Workshop Oak Ridge, Tennessee November 8 & 9, 1999
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectDisciplines
• Optical Engineering
• Electrical Engineering
• Computer Engineering
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectOutline
• Computer Networks
• Electronic and Optical Technologies
• SOME-Bus Architecture
• Optics and Electronics Implementations
• Programming Support
• Future Work
• Conclusions
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectComputer Networks
• Carries information between processors
• Influences computer system performance
• Many Variations• Shared Bus
• Point-to-Point
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectShared Bus
• Single set of wire(s) used for data exchange, e.g. Ethernet segment
• Advantages• Low wiring costs
• Direct connection between processors
• Disadvantages• Limited communication bandwidth
• Arbitration overhead
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectPoint to Point
• Dedicated sets of wires used between pairs of processors
• Advantages• Greater aggregate bandwidth
• Limited number of taps on channel
• Disadvantages• More wiring
• Processors not directly connected
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectElectronics Technology
• Advantages• Dense digital VLSI circuitry
• Inexpensive fabrication
• Disadvantages• Low fan-out of signals
• Low bandwidth per channel
• Point-to-point communication channels
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectOptics Technology
• Advantages• High fan-out of signals
• High bandwidth per channel
• Multi-cast communication channels
• Disadvantages• Single point insertion
• Weak computing facilities
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectSOME-Bus Architecture
• Exploits strengths of electronics and optics technologies
• One dedicated unidirectional channel per processor
• Each processor observes all channels
• Performance not limited by communication medium (fiber)
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectNetwork Characteristics
N processors Diameter Channels Trans-mitters
Re-ceivers
SOME Bus 1 N N (N)2
Shared Bus 1 1 N N
Mesh (N)0.5 4N 4N 4N
Hypercube Log2(N) N Log2(N) N Log2(N) N Log2(N)
Fully connected 1 N(N-1) N(N-1) N(N-1)
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectOptics Implementation
• Ribbon of multiple optical fibers
• Input coupler• One per fiber
• Multiple wavelengths of light
• Multiple processor channels on single fiber
• Output coupler• Multiple output couplers per fiber
• Bragg grating in fiber
• Wavelength specific
• Very small output per grating (~1%)
• Aligned with optical detectors
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectSOME-Bus Implementation
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectElectronics Interface
• Integrated Circuit (IC)• Array of receivers
• Interface to Processor bus
• 128 1024 byte buffers and associated logic fit in a die size of 1.6 cm x .8 cm
• Receiver Functions• Convert optical detector’s analog signal into digital signal
• Filters out uninteresting bus traffic
• Buffer data until processor bus available
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectProgramming Support
• Communication models• Shared memory
• Message passing
• Simplified model for programming• Direct connections between processors
• No interference on channel from other processors
• High-speed broadcast
• Fast barrier synchronization mechanism
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectFactors Affecting Performance
• Bandwidth is an important concern, but not the only one
• Latency is critical in many computer operations such as• Cache coherency messages
• Shared memory data exchanges
• Handshaking and synchronization signals
• Network flow control/resource allocation
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectFuture Work
• Form gratings in fibers and characterize footprint and selectivity
• Examine issues of inter-mixed analog and digital circuitry
• Build silicon v-groove devices to hold fibers for alignment with photodetectors
• Characterize performance for realistic program loads using simulations.
• Investigate whether diffractive optic elements are required, build if necessary
• Build and characterize 32 channel prototype
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectConclusions
• Bandwidth scales with the number of processors
• Network diameter = 1
• Supports shared memory, message passing and synchronization
• As technology matures, the system bandwidth will increase
Electrical and Computer Engineering
UAHSystem Level Optical InterconnectReceiver Front End Logic
Destuff
Barrier
Header Decode Length
Monitor
Buffer ControlType
DecodeAddress Decode
data_inbit_clk
reset
local_intree_outtree_in
overflow
underflow
power_dn
requestgrant
int_bus
local_addresscontrol
48
2
4
8
84
4
2
8
8 8 32
8
3