Xilinx Power Estimation Techniques and Tools

1. Power Estimation

2. Objectives • List the three phases of the design cycle where power calculations can be performed • Estimate power consumption by using the Xilinx Power Estimator worksheet • Estimate power consumption by using the XPower utility After completing this module, you will be able to:

3. Outline • Introduction • Power Estimator Worksheet • Using XPower Software • Summary

4. Power Consumption Overview • As devices get larger and faster, power consumption goes up • First generation FPGAs had: • Lower performance • Lower power requirements • No package power concerns • Today's FPGAs have: • Much higher performance • Higher power requirements • Package power limit concerns exist Package Power Limit PMAX High Density Low Density Real World Design Power Consumption Performance (MHz)

5. Power Consumption Concerns • High-speed and high-density designs require more power, leading to higher junction temperatures • Package thermal limits exist • 125oC for plastic • 150oC for ceramic • Power directly limits: • System performance • Design density • Package options • Device reliability

6. Estimating Power Consumption • Estimating power consumption is a complex calculation • Power consumption of an FPGA is almost exclusively dynamic • Power consumption is design dependent and is affected by: • Output loading • System performance (switching frequency) • Design density (number of interconnects) • Design activity (percent of interconnects switching) • Logic block and interconnect structure • Supply voltage

7. Estimating Power Consumption • Power calculations can be performed at three distinct phases of the design cycle • Concept phase: A rough estimate of power can be calculated based on estimates of logic capacity and activity rates • Use the Xilinx Power Estimator worksheets on the Web • Design phase: Power can be calculated more accurately based on detailed information about how the design is implemented in the FPGA • Use XPower™ software • System integration phase: Power is calculated in a lab environment • Use actual instrumentation • Accurate power calculation at an early stage in the design cycle will result in fewer problems later

8. Activity Rates • Accurate activity rates (A.K.A. toggle rates)are required for meaningful power calculations • Clocks and input signals have an absolute frequency • Synchronous logic nets use a percentage activity rate • 100-percent indicates that a net is expected to change state on every clock cycle • Allows you to adjust the primary clock frequency and see the effect on power consumption • Can be set globally to an average activity rate, on groups or individual nets • Logic elements also use a percentage activity rate • Based on the activity rate of output signals of the logic element • Logic elements have capacitance

9. Outline • Introduction • Power Estimator Worksheet • Using XPower Software • Summary

10. Xilinx Power Estimator • Excel worksheets with power estimation formulas built in • Enter design data in white boxes • Power estimates are shown in red boxes • Worksheet sections: • Summary (device totals) • Quiescent power • CLB logic • Block RAMs • Block multipliers • DCMs • I/O pins

11. Power Estimator Worksheet:Summary and Quiescent

12. Power Estimator Worksheet:CLB, RAM, and Multipliers

13. Power Estimator Worksheet:DCM and I/O

14. Outline • Introduction • Power Estimator Worksheet • Using XPower Software • Summary

15. What is the XPower Software? • A utility for estimating the power consumption and junction temperature of FPGA and CPLD devices • Reads an implemented design (NCD file) and timing constraint data • You supply activity rates: • Clock frequencies • Activity rates for nets, logic elements, and output pins • Capacitive loading on output pins • Power supply data and ambient temperature • Detailed design activity data from simulation (VCD file) • XPower calculates total average power consumption and generates a report

16. Running XPower • Expand Implement Design  Place & Route • Double-click Analyze Power to launch XPower in interactive mode • Use the Generate Power Data process to create reports using VCD files or TCL scripts

17. XPower GUI

18. XPower Reports • ASCII (design.pwr) or HTML (design.html) formats • Select format in the Edit  Preferences dialog • Summary of power consumption • Detailed breakdown of power usage (optional) • Thermal data • Junction temperature • Theta J-A for chosen package

19. XPower Summary Report Power summary: I(mA) P(mW) ---------------------------------------------------------------- Total estimated power consumption: 807 Vccint 1.50V: 160 240 Vccaux 3.30V: 100 330 Vcco33 3.30V: 72 237 (Additional breakdowns deleted) Thermal summary: ---------------------------------------------------------------- Estimated junction temperature: 46C 250 LFM 43C ... Ambient temp: 25C Case temp: 43C Theta J-A range: 26 - 26C/W Decoupling Network Summary: Cap Range (uF) # ---------------------------------------------------------------- Capacitor Recommendations: Total for Vccint : 8 470.0 - 1000.0 : 1 0.0470 - 0.2200 : 1 0.0100 - 0.0470 : 2 0.0010 - 0.0047 : 4 (Other power supplies deleted)

20. XPower Detailed Report Power details: ------------------------------------------------------------------------------- Clocks: Loads Loading(fF) C(pF) F(MHz) I(mA) P(mW) ------------------------------------------------------------------------------- rd_clk_inst/IBUFG Logic: rd_clk_inst/CLKDLL 40 166.7 10.0 15.0 rd_clk_inst/BUFG 6 166.7 1.5 2.3 Nets: rd_clk_dll 364 231 166.7 58.0 86.9 rd_clk_inst/CLK0 1 0 166.7 0.0 ~0.0 rd_clk_inst/IBUFG 1 0 166.7 0.0 ~0.0 . . . ------------------------------------------------------------------------------- Outputs: Loads Loading(fF) C(pF) F(MHz) I(mA) P(mW) ------------------------------------------------------------------------------- Vcco33 final_data_obuf[0] 35000 13 5.0 0.8 2.6 . . . ------------------------------------------------------------------------------- Logic: Loads Loading(fF) C(pF) F(MHz) I(mA) P(mW) ------------------------------------------------------------------------------- cha_fifo_inst/.../FIFO_BRAM.A 32 6.0 0.3 0.4 . . .

21. Outline • Introduction • Power Estimator Worksheet • Using XPower Software • Summary

22. Review Questions • Power estimations are typically made during which three phases of the design cycle? • What methods can be used to enter activity rates into the XPower tool?

23. Answers • Power estimations are typically made during which three phases of the design cycle? • Concept phase: Rough estimate based on estimated logic capacity and activity rates • Design phase: More accurate estimate based on information about how the design is implemented in the FPGA • System integration phase: Actual power usage is measured in a lab environment • What methods can be used to enter activity rates into the XPower tool? • Load a VCD file • Manually enter activity rates

24. Summary • Power calculations can be performed at three distinct phases of the design cycle: • Concept phase: (Xilinx Power Estimator Worksheet) • Design phase: (XPower software) • System integration phase: (lab measurements) • Accurate power calculation at an early stage in the design cycle will result in fewer problems later • XPower software is a utility for estimating the power consumption and the junction temperature of FPGA and CPLD devices • XPower software uses activity rates to calculate total average power consumption

25. Where Can I Learn More? • Software manuals: Development System Reference Guide • XPower chapter • Online Help from XPower GUI • Application Notes: • XAPP158: “Powering Xilinx FPGAs” • XAPP415: “Packaging Thermal Management” • Power Estimators (Excel spreadsheets): • http://www.xilinx.com/ise/power_tools/spreadsheet_pt.htm