SKILL Lint "Unrecognized global variable" error when referencing CDF default values in pcDefinePCell

Thiruvenkata,

First of all, there's a mistake throughout that article (it's an article rather than a RAK, so I couldn't find it initially as I was looking in the wrong place). It uses:

pcDefinePCell(

  list(ddGetObj(lib) cellName "layout")
  list(
    (w "float" cdf->w->defValue)
    (l "float" cdf->l->defValue)
    (layer "string" cdf->layer->defValue)
  ) ;parameters
  let((cv)

  ;body

  );let

);pcDefinePCell

The list should not be present in the formal argument list. It should just be open and close parentheses. SKILL Lint actually reports it as an error (it sees the list as a parameter which is not properly defined). So remove that. I'll request that the article is updated to correct this.

Newer IC versions correctly handle the use of the cdf variable in a let and don't complain with this code:

let((cdf lib cellName)
  lib="mylib"
  cellName="testforumpc"
  cdf=cdfGetBaseCellCDF(ddGetObj(lib cellName))

  pcDefinePCell(

    list(ddGetObj(lib) cellName "layout")
      (
        (w "float" cdf->w->defValue)
        (l "float" cdf->l->defValue)
        (layer "string" cdf->layer->defValue)
      ) ;parameters
    let(((cv pcCellView))

      dbCreateRect(cv layer list(0:0 w:l))

    );let

  );pcDefinePCell

)

I tracked down the change, and this was fixed in IC6.1.8-64b.500.30 (aka ISR30).

In the version you're using, click on the Options icon - top right of the Lint Manager assistant in the IDE - and set cdf in the Global Variables. That will stop it complaining. It's not actually global, but the SKILL Lint rule for pcDefinePCell was not written at that stage to correctly handle expressions in the value part of a parameter definition.

Regards,

Andrew

Thanks Andrew,

As a follow-up, are the variables lib, cell, and cdf defined outside pcDefinePCell saved in the data.dm file? How does the PCell retrieve the cdf variable values each time without requiring the source code to be loaded in every session? Could the variables be saved in data.dm file?

Thanks Andrew,

As a follow-up, are the variables lib, cell, and cdf defined outside pcDefinePCell saved in the data.dm file? How does the PCell retrieve the cdf variable values each time without requiring the source code to be loaded in every session? Could the variables be saved in data.dm file?

No, nothing is saved in the data.dm (not sure why you mention that - nothing to do with the PCell is saved in the data.dm). The lib/cell/cdf variables are only accessible in the first argument and second argument of pcDefinePCell (i.e. the cellView description and the formal parameters); they cannot be referred to in the body of the pcDefinePCell - that is evaluated each time a variant is constructed.

Why would you need them to be saved in the data.dm? Within the body you know the lib and cell - it's pcCellView~>libName and pcCellView~>cellName - and if you need to get the base CDF (not sure why you'd want this - it's generally not a good idea) - you could use cdfGetCellCDF or cdfGetBaseCellCDF within the PCell code to find it again.

Andrew 

Thank you, Andrew, for the clarification. I realize now that I misunderstood how this works.

I was under the impression that an expression like cdf->layer1->defValue remained dynamically linked and was re-evaluated every time a PCell instance was created. I now understand that pcDefinePCell evaluates that expression immediately when the SKILL file is loaded, and the resulting value is stored as the default parameter value in the PCell master. In that sense, cdf is only used temporarily during that initial evaluation.

I also mistakenly assumed that the compiled PCell code itself was stored in the data.dm file, which is why I brought up data.dm earlier. That was my misunderstanding.

thiruvenkata said:

I also mistakenly assumed that the compiled PCell code itself was stored in the data.dm file, which is why I brought up data.dm earlier. That was my misunderstanding.

Ah, that clarifies why you asked. The PCell code is actually stored in the cellView itself (i.e. in the layout, schematic or symbol database).

Andrew