power estimation by RTL-Compiler

 Hi Ali,

I believe this is some of the information you are looking for

rc:/> get_attr -h lp*default* *

Usage: get_attribute <string> [<object>+]

    <string>:
        attribute name
    [<object>+]:
        object of interest (must be unique)

    attribute categories: lp_tcf tim

    attribute name: lp_default_toggle_percentage
          category: tim (controls timing optimization and returns timing information)
       object type: clock
       access type: read-write
         data type: fixed point
     default value: no_value
              help: Default toggle-rate scale-factor of data signals based on clocks.

    attribute name: lp_default_probability
          category: lp_tcf (returns switching activity information)
       object type: instance
       access type: read-write
         data type: fixed point
     default value: 0.50000
              help: Default probability for all nets within the hierarchical instance to be high.

    attribute name: lp_default_toggle_rate
          category: lp_tcf (returns switching activity information)
       object type: instance
       access type: read-write
         data type: fixed point
     default value: 0.02000
             units: /ns
              help: Default signal toggle rate for all nets within the hierarchical instance.

    attribute name: lp_default_probability
          category: lp_tcf (returns switching activity information)
       object type: design
       access type: read-write
         data type: fixed point
     default value: 0.50000
              help: Default probability for all nets in current design to be high.

    attribute name: lp_default_toggle_rate
          category: lp_tcf (returns switching activity information)
       object type: design
       access type: read-write
         data type: fixed point
     default value: 0.02000
             units: /ns
              help: Default signal toggle rate for all top level nets in current design.

rc:/> get_attr program_version /
v08.10-s125_1

Note that I included the RC version I was using since this may have changed in recent release. I strongly encourage you to look at the low power user guide since there is ample information there, not only about what you are asking, but also as to how activity is propagated and other information you may find of value such as looking at power vs. time dynamic activity and other useful low power features.

good luck,

gh-

 BTW, I meant the RTL Compiler Low Power User Guide

gh-

 Thanks,

if the default toggle rate is 0.02 (1/ns), then is it changed by only setting clock period? or toggle rate should be set by setting its attribute?

I have a clock period of 500ps and default probability is 0.5 and I didn't tuch toggle rate attribute. In this case can I say that the power is reported for toggle rate of 1/250 ps == 4G, although timing shows a neg. slack time of -450?

Thanks,

Ali 

 Hi Ali,

 the answer to your question is no. toggle activity is independant from clock definitions on SDC. In general, dynamic power analysis with default rates is not terribly accurate. I suggest you use VCD, TCF, or SAIF from simulation to produce more accurate results. VCD is nice in that it allows you to look at time vs. power profile which further enable you to address the block responsible for peak power surges. If you have access to Palladium emulation and power is a hot ticket item for your team, I would certainly inquire about DPA.

 gh-

 PS: Please post RC questions in Logic Design forums. I think you will get more replies there