Power Visualization, Analysis, and Optimization Tools for FPGAs Matthew French, Li Wang and Michael Wirthlin USC, Information Sciences Institute, BYU

Outline Introduction Background JDHL Tool Suite Power Visualization Power Analysis Tools Power Modeling Power Optimization Conclusion

Introduction Many devices demand low power in order to increase functional lifetime –CLBs max operating frequency rapidly (exponentially) increasing –Operating voltages decreasing much slower Result: Exponentially increasing maximum power consumption per device

Low-Power Intelligent Tool Environment Object oriented tool set for Power Visualization via JHDL Uses: –Circuit logic –FPGA architecture –Power information

LITE Take models and power analysis tools and create a power optimization algorithm –Algorithm development is supported through the user of tools to query and sort circuit characteristics and drop in COTS CAD tool compliant constraints.

Background Low Power FPGA Designs –Address VLSI designs of FPGAs Synthesis-Level power optimizations –Mapping to LUT-based FPGA techniques –Reduce glitching power through pipelining CAD algorithms for PAR

Background Offer “point” solutions –Little user control / feedback Synthesis - PAR optimized for Speed / Area Current tools limited –Readability –Entry point in FPGA design flow Current estimates: –Manually estimating

FPGA’s in Low Power Environments Three Needs: 1.Monitor power consumption early in design process 2.Captures data-dependent transients and overall power consumption 3.Perform real-time constrain-driven automated power optimizations like the Area / Timing constraints are done today

JHDL Tool Suite JHDL Background EDIF Import Parser Cross Tool Naming and Correlation

JHDL Background Create complex, high speed FPGA circuit modules programmatically from within Java. Design Aids: –Digital circuit simulator –Circuit hierarchy browser –FPGA library primitives –Tools for exporting to EDIF and VHDL

JHDL / LITE Interoperation with existing commercial tool flows based on an HDL, through seemless JHDL-EDIF translation. Single user interface GUI event API developed –New tools to fully interact with JHDL

EDIF Import Parser Development of new EDIF netlist tool –Developed independently from JDHL –Supports parsing of large EDIF netlists / merge multiple EDIF files –JHDL export feature added EDIF Parser provides LITE tool suite –Capability to import 3rd party FPGA design –Provides consistent circuit database

Figure 2

Cross Tool Naming Correlation Ability to correlate design resources between: –EDIF, JHDL, LITE, COTS PAR tool flow Difficulty: Different vendor specific names and JHDL simulation interpret names –“Original” (Xilinx) –“Valid” (JHDL) Added Name management resource

Figure 3

Power Visualization Tree-view of circuit and shows cumulative power consumption of each module in circuit –Sorted by power consumption Plot of instantaneous power history of selected cells over time –Focuses on power modes / operating modes –Identify and characterize modes for different scenarios (Temporal view)

Figure 4 modes power

Power Visualization Simulation uses capacitance values: –Post PAR via Xilinx’s XPower –Pre PAR via Power Modeling A variety of modeling algorithms can be used Simulator work with design during both Pre and Post PAR = more accurate modeling with a fully routed design

Power Analysis Tools XDL Importer –Detailed information of how a circuit was mapped, placed, and routed to be captured by JHDL environment XPR Importer –Capture Xilinx’s XPower outputs Post PAR circuit modeling Create capacitance libraries of components and interconnect capacitance values

Power Analysis Tools Two types of plots to visualize and verify power and architectural mapping correlations. –Interconnect Histogram Number of each interconnect resources –Long Lines, Direct Connections, Double Lines, Hexagonal Lines, Programmable Interconnect Points –Net Characteristic Plot Plot capacitance vs. net length, number of PIPs, or number of loads for every net in the diagram

Figure 5

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Power Modeling Move power considerations to front of tool flow –Accurate models required to estimate and predict power consumption Power Analysis tool: –Synthesized circuit compared to PAR –Allows development and experimentation of power models Toggle rate only Exact timing-level PAR circuit

Power Modeling Lite exploits extensible JHDL data types –Representing hierarchical structure and connectivity of circuits of a FPGA –Data types augmented with load estimates for each net and cell Dynamic power consumption

Power Modeling Capacitance –FPGA logic resource Published / extracted from Xpower reports –Interconnect route resource drives Most difficult to model Unknown until PAR Fanout = strong predictor of net capacitance –80% accuracy predicting where nets would be mapped –3.2% mean power prediction error –1.2% standard deviation

Power Optimization Specifically - Routing and interconnect power dissipation –50-70% of FPGA dynamic power consumption is dissipated in clocking and interconnection network –Will not functionally alter user’s design –Future: EDIF Parser does provide API for synthesis level circuit mapping modifications which could be incorporated into power mapping API

Power Optimization Allows user to combine COTS CAD tool constraints (timing and placement) with results from Power Analysis to meet designer’s needs.

Figure 7

Clock Table Clock Table similar in appearance and capabilities but is tailored for clock analysis. –Toggle Rate –Number of sink flip-flops –Capacitance –Power consumption

Figure 8

Power Optimization Algorithms Slack minimization –Compares combinational logic delay of a net with its timing specification –Tightens the timing constraints on nets with the potential for long interconnects Clock tree minimization –Place logic close to “trunk” of clock distribution tree

Power Optimization Algorithms 2-terminal net co-location –Placing unity fanout signals tightly to use direct connects or internal slice routing Area minimization –Balance clock tree paring with West - East signal routing (Virtex architecture)

Results (?) Combine power optimization techniques –average dynamic power reduction 10.2% –peak reduction power reduction 19.4%

Conclusion Introduces LITE –Uses JHDL to address: Power visualization –Power consumption logic level tree view Power analysis –Interacts with COTS CAD tools Power optimization algorithms Elevate level of abstraction closer to design entry point