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XPower for
CoolRunner™ XPLA3
CPLDs
Overview
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Design power considerations
Power consumption basics of CMOS devices
Calculating power in CoolRunner XPLA3 CPLDs
Assumptions for XPLA3 CPLDs in XPower
CoolRunner XPLA3 power model in XPower
Rank of power consuming nets in XPLA3 CPLDs
Activity rates
Data entry methods
Improving accuracy of XPLA3 power estimation
Macrocell configuration examples
Quick Start Training
Objectives
• Power consumption in CoolRunner XPLA3 CPLDs
• Assumptions for XPLA3 CPLDs in XPower
• Applying the CoolRunner XPLA3 power model to a
design
• The highest power consuming nets in XPLA3 CPLDs
• Types of activity rates
• Types of Data Entry Methods
• Improving accuracy of XPLA3 power estimation
• Applying different macrocell configurations to XPower
• XAPP360
Quick Start Training
Power Considerations
• Power Supply requirements
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Batteries
DC/DC converters
AC power source
Power supply voltage
• Thermal requirements
– Package types
– Enclosed environments
– Industrial applications
• CoolRunner XPLA3 CPLDs
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Low Power
Low Junction Temperature
Very predictable power consumption
Fast
• XAPP360
– http://www.xilinx.com/xapp/xapp360.pdf
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 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
Quick Start Training
Calculating Power for
CoolRunner
• Calculating Dynamic Current is a overwhelmingly tedious task
• XPower is necessary for this calculation
• Dynamic Current equation
I Dynamic  C  V  f
• Total Current equation
I Total  I Dynamic  I Static
ITotal  C V  f  I Static
• Total Power equation
PTotal  ITotal V
Quick Start Training
XPower Assumptions for
XPLA3
• 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
– 800 ps
– Correlated in lab at 800 ps
– Actual transitions slower than 800 ps 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
Quick Start Training
XPLA3 Power Model
• Simplified model of the CoolRunner XPLA3 architecture
• Somewhat encoded 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
Quick Start Training
XPLA3 Power Model
• Nets adjustable by the user
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I - Input
Q - Flip flop output
D - Flip flop input from OR term
N - ZIA feedback
P - ZIA feedback
PT - Product Term output
Quick Start Training
• Nets NOT adjustable by the user
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ZIA - Interconnect Array
OR - Output of OR term
UCT - Universal Control Term
FF - Macrocell control inputs
XPLA3 Power Consumption
• Nets in order of power consumption
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External Capacitance - Very High
O - High
UCT - High - Larger with high density devices
I - High - Larger with high density devices
P - Medium - Somewhat larger with high density devices
N - Medium - Somewhat larger with high density devices
ZIA - Medium
PT - Low
OR - Low
FF - Low
Q - Very Low
D - Very Low
Quick Start Training
Activity Rate
• Absolute Frequency
– Frequency of a net in units of MHz
– All nets (except Q) in CoolRunner XPLA3
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 XPLA3 CPLDs
• Based on global clocks only
• When using product term clocks or UCT
clocks, give data in absolute frequency
– Great for “What if?” scenarios
Quick Start Training
Data Entry Methods
• Data entry by hand
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Most accurate, but most tedious method
Requires very detailed knowledge of XPLA3 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
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
Quick Start Training
Estimate Activity Rates Tool
• Sets absolute frequencies only
• Automatically set nets
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UCT
O
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ZIA
PT
OR
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• Nets not automatically set
– External Capacitance
– Q
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
Quick Start Training
Improving Accuracy (cont.)
• Macrocell configurations
– Users are not exposed to product term numbers
– ZIA is modeled as a non-inverting buffer
– Macrocells have many configurations, but are
understandable
– 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
Quick Start Training
Combinatorial Output
Macrocell
• Set activity rates of these nets
– N - Absolute Frequency
– P - Absolute Frequency
– O - Absolute Frequency
• Set by XPower automatically
• Based on I/O pin activity rate
– D - Absolute Frequency
• Set by Estimate Activity Rates
tool
• Based on activity rate of OR
term
Quick Start Training
Registered Output Macrocell
• Set activity rates of these nets
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Q - Toggle Rate
N - Absolute Frequency
P - Absolute Frequency
O - Absolute Frequency
• Set by XPower automatically
• Based on I/O pin activity rate
– D - Absolute Frequency
• Set by Estimate Activity Rates
tool
• Based on activity rate of OR term
– FF - Absolute Frequency
• Set by XPower automatically
Quick Start Training
Summary
• XPower is a necessity for
– Low power designs
– Designs with a thermal budget
– Battery operated designs
• XPower support for CoolRunner XPLA3 available now
– Xpower support for CoolRunner-II coming in ISE v6.1i
• Simulation with ModelSim XE
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Easiest method
Reduces the chance of data entry error
Provides accurate activity rate information
Requires user to modify fewer nets in XPower
• CoolRunner CPLDs
– Lowest power CPLD in the industry
– Excellent for handheld, battery powered designs
– XPower makes it easier to show customers power savings using their designs
Quick Start Training