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 ELC: liberty file output capacitance index different from simulation 

Last post Wed, Oct 28 2009 6:24 PM by Brian Harrison. 2 replies.
Started by Brian Harrison 27 Oct 2009 07:56 PM. Topic has 2 replies and 1826 views
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  • Tue, Oct 27 2009 7:56 PM

    ELC: liberty file output capacitance index different from simulation Reply

    When generating a liberty dotlib for a bi-directional buffer, I have noticed that the cap index differs from what was used in the simulation.  This only affects the PAD of the buffer and not the internal output.  It appears to add the capacitance of the ouput pin(PAD) to the simulated value.

    Example:

     Using this in my setup file:

    Index    CLASS_A  {

            load =  3.0000p   4.1667p   5.3333p   6.5000p   7.6667p   8.8333p   10.0000p  ;

     I get the following from the generated liberty file.  Not capacitance of pin is listed in the dotlib as 2.124p

            index_2 ("5.12392, 6.29062, 7.45722, 8.62392, 9.79062, 10.9572, 12.1239");    p

     

     When the bi-buf is simulated as an input, the core output pin cap index match my internal index load, also noted that core output pin cap is 0.

     

    Is there a way to turn this off to not add the total net capacitance of the pin and index load.  I'm trying to compare modifications to an IO cell and see if they affect timing, however because the PAD ouput has changed slightly I get different indexes.

     

    Thanks.

     

    • Post Points: 20
  • Wed, Oct 28 2009 3:33 PM

    • WilsonK
    • Not Ranked
    • Joined on Wed, Oct 21 2009
    • Posts 3
    • Points 45
    Re: ELC: liberty file output capacitance index different from simulation Reply

    Hi Brian,

    Please file a SR or CCR.

    Wilson 

     

     

    • Post Points: 20
  • Wed, Oct 28 2009 6:24 PM

    Re: ELC: liberty file output capacitance index different from simulation Reply

     It appears that the alf2lib function is what is causing the problem.  The data tables and indexes are correct in the alf file. 

    This is what I'm using:

    alf2lib -alf IO.alf  -lib .IO.lib -max_load -supply VCC -slew_derate 1.0 -def IO.prop -state
     

    I have project restrictions from the customer on the data, but I'll see what I can do.  Any other switches I can add to the alf2lib ?

    • Post Points: 5
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Started by Brian Harrison at 27 Oct 2009 07:56 PM. Topic has 2 replies.