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Published byIra Griffith Modified about 1 year ago

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XPower for CoolRunner™-II CPLDs

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Quick Start Training Overview Design power considerations Power consumption basics of CMOS devices Calculating power in CoolRunner-II CPLDs Assumptions for CoolRunner-II CPLDs in XPower CoolRunner-II power model in XPower Rank of power consuming nets in CoolRunner-II CPLDs Activity rates Data entry methods Improving accuracy of CoolRunner-II power estimation Design example

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Quick Start Training Objectives Power consumption in CoolRunner-II CPLDs Assumptions for CoolRunner-II CPLDs in XPower Applying the CoolRunner-II power model to a design The highest power consuming nets in CoolRunner-II CPLDs Types of activity rates Types of Data Entry Methods Improving accuracy of CoolRunner-II power estimation Understanding a simple design example using XPower XAPP360

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Quick Start Training Power Considerations Power Supply requirements – Batteries – DC/DC converters – AC power source – Power supply voltage Thermal requirements – Package types – Enclosed environments – Industrial applications CoolRunner-II CPLDs – Low Power – Low Junction Temperature – Very predictable power consumption – Fast XAPP360 –

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Quick Start Training Power in a CMOS Device Total Current is composed of two types of current – Static – Dynamic Static Current – Leakage current in the turned off transistor channel – Ideally zero – Fixed component of Total Current Dynamic Current – Switching of the CMOS gate when in the linear region causing transition (crowbar) current Transition time is very fast Relatively small component – Charge/Discharge of capacitive poly gate in subsequent logic element – XPower combines transition current with capacitive current in the power model

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Quick Start Training Calculating Power for CoolRunner CPLDs Calculating Dynamic Current is an overwhelmingly tedious task XPower is necessary for this calculation Dynamic Current equation Total Current equation Total Power equation fVCI Dynamic

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Quick Start Training XPower Assumptions for CoolRunner-II CPLDs Voltage – Within published operating limits – Constant (no spikes or dips) – User must enter appropriate value Timing and frequency – Within published operating limits – Operation above limits yields inaccurate power calculations Input transition times – 1.5 ns – Correlated in lab at 1.5 ns – Actual transitions slower than 1.5 ns will: Increase actual power consumption Cause XPower data to appear lower than actual Lumped capacitance – Logic elements (Product Terms, etc.) – Used to create a power model

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Quick Start Training CoolRunner-II Power Model Simplified model of the CoolRunner-II architecture Somewhat encrypted net names – FB1_PT12 Product Term #12 in Function Block #1 – FB1_3_Q Q Flip Flop output of Macrocell #3 in Function Block #1 – FB4_12_I Input net of Macrocell #12 in Function Block #4

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Quick Start Training CoolRunner-II Power Model Nets adjustable by the user – I - Input from I/O – Q - Flip flop output – FB - Feedback to the AIM – PT - Product Term output – MC_CLK - Macrocell control inputs – OR - Output of OR term Nets NOT adjustable by the user – AIM - Interconnect Array – AND - Input to the register – MC_OE - Output Enable signal – RST/PST - Reset/Preset inputs to register

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Quick Start Training CoolRunner-II Power Consumption Nets in order of power consumption – External Capacitance - Very High – O - High – GCK - High - Larger with high density devices – FB - Medium - Larger with high density devices – AIM - Medium – I - Low - Medium for Differential Inputs – PT - Low – OR - Low – AND - Very Low – MC_CLK - Very Low – RST/PST - Very Low – MC_OE - Very Low – Q - Very Low

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Quick Start Training Activity Rate Absolute Frequency – Frequency of a net in units of MHz – All nets (except Q) in CoolRunner-II CPLDs are specified with absolute frequency Toggle Rate – A percentage of the clock frequency Entered as a percentage value Displayed as MHz based on clock frequency 100% toggle rate yields 1/2 frequency of the clock – Q nets in CoolRunner-II CPLDs Based on global clocks only When using product term clocks give data in absolute frequency – Great for “What if?” scenarios

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Quick Start Training Data Entry Methods Data entry by hand – Most accurate, but most tedious method – Requires very detailed knowledge of CoolRunner-II architecture – Must specify activity rates for all nets – Depending on the design, it may be nearly impossible to determine activity rates for all nets Estimate Activity Rates tool – Algorithm estimates absolute frequencies of nets not yet set by the user – Does not estimate toggle rates – Alleviates the tedium, but is less accurate than data entry by hand – Must enter all absolute frequencies for primary I/Os by hand – Must enter all toggle rates by hand including buried registers

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Quick Start Training Data Entry Methods (cont.) Simulation with ModelSim XE – Easiest method – Value Change Dump (VCD) file contains frequency data – Simulate for sufficient length of time – Currently, only top level nets are contained in VCD file – Hand edit remaining primary I/Os and registers including buried registers – Use Estimate Activity Rates tool

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Quick Start Training Estimate Activity Rates Tool Sets absolute frequencies only Automatically set nets – O – GCK – I – FB – AIM – PT – AND – OR – MC_CLK – RST/PST – MC_OE Nets not automatically set – External Capacitance – Q

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Quick Start Training Improving Accuracy External capacitance loads – Loads connected to the I/O pin Printed circuit board trace capacitance Capacitive load of external devices – Current is derived from Vcc and GND pins to charge and discharge this load – Large source of power consumption Dramatic effect on power consumption Reduce external loads to reduce power consumption – For accurate power estimates Provide accurate capacitance value to XPower Provide accurate absolute frequency of external load

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Quick Start Training Improving Accuracy (cont.) Macrocell configurations – Users are not exposed to product term numbers – AIM is modeled as a non-inverting buffer – Macrocells have many configurations, but are understandable by the user – This information is most useful for Data entry by hand method Double checking the Estimate Activity Rates tool – Proper activity rate information is necessary in the macrocell Improves accuracy Source of all net activity rates

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Quick Start Training Registered Output Macrocell Remaining nets automatically set by XPower using Estimate Activity Rates Set activity rates of these nets – I - Input signal Absolute Frequency – GCK - Global Clock Absolute Frequency – Q - Register output Toggle Rate

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Quick Start Training Summary XPower is a necessity for – Low power designs – Designs with a thermal budget – Battery operated designs Simulation with ModelSim XE – Easiest method – Reduces the chance of data entry error – Provides accurate activity rate information – Requires user to modify fewer nets in XPower CoolRunner-II CPLDs – Lowest power 1.8V CPLD in the industry – Excellent for handheld, battery powered designs – XPower makes it easier to see power savings using the your own designs XPower support for CoolRunner-II will be available in ISE 6.1i

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