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Using Inherited Parameters in PCells

msharma

 Friends,

 I am creating a custom pcell, through the graphical layout method. The custom pcell layout contains an instance of a pdk pcell. I have inherited a parameter 'width' among others from the pdk pcell to my custom pcell. In my custom pcell, I need to repeat contacts based on the value of width. But, it is not possible to use parameter 'width' in repetition expressions. The software gets confused, and assigns 'width' as a new parameter.

 

Do you know how to reference the inherited 'width' parameter in my custom pcell, without confusing the software? Any responses are appreciated.

 

Thanks,

Mohit

  • Andrew Beckett

    Mohit,

    Well, it works for me - so I assume you must be doing something wrong. Have you set up the instance of the pdk pcell to have an inherited parameter using Pcell->Inherited Parameters? I just did that, and assigned my instance to inherit from a parameter called "width" and then also used width in my repetition expression - and also used Parameters->Edit to set the default value of width.

    From what you describe you're expecting the parent pcell to inherit from the child instance, which doesn't make sense - how would the child pcell know what values to use?

    If this doesn't help, I think you're going to have to post some pictures and a more detailed explanation, or contact customer support.

    Regards,

    Andrew.

  • msharma
    Andrew, thanks for the reply. I tried this one more time, and still no success. Therefore, I have attached some screenshots Error when using PCell in a new layoutError messgae from CDS.logPCell master layout

    layout_failed

    CDSlog

    layout

    ModifyRepeat_inX

    Define-ModifyInheritedParameters

    Edit Parameters

    This is my first time with images on the forum, so I hope you can see the images.

    Mohit
  • msharma

     Andrew,

     

    I posted the screenshots of the PCell creation on Flickr. You can see them here:

    http://www.flickr.com/photos/78766415@N02/with/7051464299/

     

    As for  your question:

    "From what you describe you're expecting the parent pcell to inherit from the child instance, which doesn't make sense - how would the child pcell know what values to use?"

     

    It seems the Cadence software passes the value assigned to width to the inherited PCell. I was able to verify that when using this hierarchical PCell, the width changes to the avlue assigned to each instance. It's when using the parameter width for repetition that the PCell breaks down.

     

    Thanks,

    Mohit

  • Andrew Beckett

    Mohit,

    From looking at your pictures, it's failing because when the instantiation of the child pcell is happening, it is expecting a string, not a float - although the error message appears to say that it's expecting 2e-12 (not sure why that is). I see that the length is being passed as a string - so I'd have expected the width to be the same type. 

    So my guess (without seeing the actual data) is that you should change the type of width to be a string, and then make your stepping distance in the repetitions equal to cdfParseFloatString(width)/2 .

    If this doesn't help - I'd suggest going via customer support - this kind of thing is much easier if we can see the actual data. As a colleague of mine used to say - "a picture is worth a thousand words, but a database is worth a million"

    Regards,

    Andrew. 

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