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defstruct in pcell (for layout), is it possible?

sjoerdh

Hello,

This is what I want to do:

  • Create a pcell that instantiates other pcells (layout)
  • Perform various "measurements" on this new instance (i.e.: retrieve the bounding box)
  • This information has to be used lateron in the pcell code

I'd like to store this information in a table, where each cell is a defstruct.The code looks like this:

procedure( genCurMir( ... )
    let( ()
        ...
        curMirInst = makeTable( "curMirInst" nil )
        defstruct( instance boundingBox gateCenter drainCenter sourceCentre )
        curMirInst["CELL1"] = make_instance()
        ...
        curMirInst["CELL1"]->boundingBox = instID~>bBox
        ...
    ) ;;; end of let
) ;;; end of procedure genCurMir

After generating the pcell (loading the code containing the command "pcDefinePCell") weird things happen: I am unable to open any view (layout/schematic/symbol/...).Entering commands in the CIW will result (9 out of 10 times) in an error, which is the same error when trying to open any cell-view:

*Error* setq/set: Variable is protected and cannot be assigned to - instance

I have tried creating the defstruct with an other name (blablablabla, definitely not used anywhere else), but the same error, only "instance" replaced by "blablablabla". I have to restart Cedence to regain control.

Furthermore, this created defstruct seems to be global, whereas I created it inside a let. I'd like to keep it local though.

So my question is:

Is it possible to use defstructs in pcells?
If so, what am I doing wrong?

I'd realy like to use this method (table of defstructs) since it is very conveniant.

Any help is highly appreciated.

Thanks in advance,

Sjoerd

Parents

  • Hi Sjoerd

    You are re-creating the defstruct each time your pcell code evaluates. As you saw, the defstruct is a global object that can only be made once. You can then instantiate it inside of the pcells without any issues, keeping it in your table of defstructs. I would create the defstruct outside the pcDefinePCell statement and do it only once per PDK or check for its existance before creating it.

    Move this line outside the pcDefinePCell statement:

            defstruct( instance boundingBox gateCenter drainCenter sourceCentre )

    If you absolutely want the memory to be reclamed, use a DPL - disembodied property list or another table.

    Ted

     

Reply

  • Hi Sjoerd

    You are re-creating the defstruct each time your pcell code evaluates. As you saw, the defstruct is a global object that can only be made once. You can then instantiate it inside of the pcells without any issues, keeping it in your table of defstructs. I would create the defstruct outside the pcDefinePCell statement and do it only once per PDK or check for its existance before creating it.

    Move this line outside the pcDefinePCell statement:

            defstruct( instance boundingBox gateCenter drainCenter sourceCentre )

    If you absolutely want the memory to be reclamed, use a DPL - disembodied property list or another table.

    Ted

     

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