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OCV mode optimization in encounter

MadhuNS

Hi All,

Its been a general practise with our BE folks to use BCWC mode with some derate and dubb it as "equivalent" to OCV mode.

Its been a nighmarish to close design via ECO since timing engines using true OCV modes show much skewed timing when compared with encounters native timer.

Is there an OCV mode in encounter ? Since I'am novice wrt encounter grapevine says that since two libraries are required for OCV mode its not recommended,

which brings me to the next point has any one figured out a way to derate ECSM/NLDM library and use the derated library as the second library required by OCV.

Parents

  • Yes, Encounter does support OCV mode both for timing analysis and for optimization.  To enable it, use the setAnalysisMode command:

    setAnalysisMode -analysisType onChipVariation

    However, it is crucial to understand that if you set up the tool with max and min libraries via a .conf file and enable onChipVariation timing that the software will use the min library for timing the capture clock paths.  This is probably not what you want (the difference between the max and min .libs is likely quite large which will lead to very large clock skew).  From a timing analysis perspective, this quandry can be resolved by pointing to only the max .libs for setup analysis and only the min libs for hold analysis.  For optimization purposes, this can be resolved by establishing the timing environment using MMMC (mulit-mode/multi-corner) mechanisms- even if you have only a single setup corner and a single hold corner.

    This approach is elaborated on in detail in documentation (and a complete flow) in the 8.1 release of Encounter as part of the newly released Foundation Flows.  Log in with your Sourcelink account to access more information here:

    http://sourcelink.cadence.com/docs/files/Release_Info/Docs/flatImpl/flatImpl8.1/flow.html

    I'm not sure I understand the last piece of your question regarding derating libraries.  I've not come across this before myself.  Maybe someone else can provide additional information on that subject.

    Hope this helps,
    Bob

Reply

  • Yes, Encounter does support OCV mode both for timing analysis and for optimization.  To enable it, use the setAnalysisMode command:

    setAnalysisMode -analysisType onChipVariation

    However, it is crucial to understand that if you set up the tool with max and min libraries via a .conf file and enable onChipVariation timing that the software will use the min library for timing the capture clock paths.  This is probably not what you want (the difference between the max and min .libs is likely quite large which will lead to very large clock skew).  From a timing analysis perspective, this quandry can be resolved by pointing to only the max .libs for setup analysis and only the min libs for hold analysis.  For optimization purposes, this can be resolved by establishing the timing environment using MMMC (mulit-mode/multi-corner) mechanisms- even if you have only a single setup corner and a single hold corner.

    This approach is elaborated on in detail in documentation (and a complete flow) in the 8.1 release of Encounter as part of the newly released Foundation Flows.  Log in with your Sourcelink account to access more information here:

    http://sourcelink.cadence.com/docs/files/Release_Info/Docs/flatImpl/flatImpl8.1/flow.html

    I'm not sure I understand the last piece of your question regarding derating libraries.  I've not come across this before myself.  Maybe someone else can provide additional information on that subject.

    Hope this helps,
    Bob

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