XPower Analyzer
Understanding Toggle Rates
Toggle Rate reflects how often an output changes relative to a given clock input and can be modeled as a percentage between 0-200%. The toggle rate of 100% means that if the clock frequency is 100 MHz, a data toggle rate of 100% equates to a data frequency of 50 MHz. This convention stems from an assumption that a net with 100% toggle rate toggles every rising (or falling) edge of a clock whose frequency is specified. You must select Tools > Update Power Analysis to make sure any change is applied to the design.
Realistic toggle rates, along with loading a SAIF or VCF file should be used to achieve optimal power results.
Toggle Rates are the rate at which a net or logic element switches. In some cases (synchronous logic), they are entered as a percent of the driving clock’s rate. For dynamic power calculation and display, toggle rates are expressed as a frequency.
A toggle rate is relative to a clock, in that the net or logic element switches at some percentage of the clock frequency. The values range from 0 to 100, where 100% yields 1/2 the clock frequency. For nets and logic that are not synchronized with a clock, the toggle rate is just the switching rate.
The toggle rate of any individual I/O connected to a synchronous element may be adjusted due to an enable rate of the synchronous element.
After you change a global toggle rate setting like FF Toggle Rate, I/O Toggle Rate, or DSP Toggle Rate, select Tools > Update Power Analysis to ensure the toggle rate changes are applied throughout the design and that new estimates are obtained.
See Also

Copyright © 2008, Xilinx® Inc. All rights reserved.