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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
  • Andrew Beckett

    Hi Sjoerd,

    First of all, there is no problem with the defstruct using a global object to store its definition. After all, that's what your functions are too - these are globally named functions (unless you use lexical scoping in SKILL++ to have local functions, or potentially using the namespace mechanism in IC616 (I wouldn't recommend that currently since it needs some refinement in my opinion)). You're not really using a global object to communicate data - it's just a global definition - after creation you don't change it. So the trick is simply to give it a sensible prefix, which is what you should do with your functions too.

    Now, on to your question. Your table of tables is NOT a table of tables. It's a table, indexed by a list. Because of that, you have more keys in there than you really want. You could of course just filter them (using setof):

    foreach(key sortcar(setof(k tempInst cadr(k)=="name") 'lessp)  printf( "%L\n" tempInst[key]))

    Or have a conditional:

    foreach(key  sortcar( tempInst->? 'lessp) when(cadr(key)=="name" printf("%L\n" tempInst[key])))

    Or actually implement it as a table of tables! This is what I would do if I was implementing this without a defstruct - it means your keys in the top table are what you actually want them to be, rather than making the keys a compound of the real index and the slot name. So for example:

    tempInst=makeTable( 'tempInstTable nil )
    tempInstDS[1] = makeTable('instThing nil)
    tempInstDS[2] = makeTable('instThing nil)
    tempInstDS[3] = makeTable('instThing nil)
    tempInstDS[1]->instName = "instC"
    tempInstDS[2]->instName = "instB"
    tempInstDS[3]->instName = "instA"
    tempInstDS[1]->instOrient = "R90"
    tempInstDS[2]->instOrient = "R180"
    tempInstDS[3]->instOrient = "MX"

    Then you can use the rest of the code exactly as you did with the defstruct implementation. So for example:

    foreach(key sort(tempInstDS->? 'lessp) printf("%L\n" tempInstDS[key]->instName ))

    This works because rather conveniently if you have a table with symbols as the keys you can do:

      table->instName="instD"

    which is exactly the same as doing:

      table['instName]="instD"

    but has the readability of it being a defstruct or a DPL. It also makes it very easy to change a code implementation originally built using DPLs to tables, which can lead to a big efficiency improvement since DPLs are sequential, compared with tables which are hashed.

    Kind Regards,

    Andrew.

Reply
  • Andrew Beckett

    Hi Sjoerd,

    First of all, there is no problem with the defstruct using a global object to store its definition. After all, that's what your functions are too - these are globally named functions (unless you use lexical scoping in SKILL++ to have local functions, or potentially using the namespace mechanism in IC616 (I wouldn't recommend that currently since it needs some refinement in my opinion)). You're not really using a global object to communicate data - it's just a global definition - after creation you don't change it. So the trick is simply to give it a sensible prefix, which is what you should do with your functions too.

    Now, on to your question. Your table of tables is NOT a table of tables. It's a table, indexed by a list. Because of that, you have more keys in there than you really want. You could of course just filter them (using setof):

    foreach(key sortcar(setof(k tempInst cadr(k)=="name") 'lessp)  printf( "%L\n" tempInst[key]))

    Or have a conditional:

    foreach(key  sortcar( tempInst->? 'lessp) when(cadr(key)=="name" printf("%L\n" tempInst[key])))

    Or actually implement it as a table of tables! This is what I would do if I was implementing this without a defstruct - it means your keys in the top table are what you actually want them to be, rather than making the keys a compound of the real index and the slot name. So for example:

    tempInst=makeTable( 'tempInstTable nil )
    tempInstDS[1] = makeTable('instThing nil)
    tempInstDS[2] = makeTable('instThing nil)
    tempInstDS[3] = makeTable('instThing nil)
    tempInstDS[1]->instName = "instC"
    tempInstDS[2]->instName = "instB"
    tempInstDS[3]->instName = "instA"
    tempInstDS[1]->instOrient = "R90"
    tempInstDS[2]->instOrient = "R180"
    tempInstDS[3]->instOrient = "MX"

    Then you can use the rest of the code exactly as you did with the defstruct implementation. So for example:

    foreach(key sort(tempInstDS->? 'lessp) printf("%L\n" tempInstDS[key]->instName ))

    This works because rather conveniently if you have a table with symbols as the keys you can do:

      table->instName="instD"

    which is exactly the same as doing:

      table['instName]="instD"

    but has the readability of it being a defstruct or a DPL. It also makes it very easy to change a code implementation originally built using DPLs to tables, which can lead to a big efficiency improvement since DPLs are sequential, compared with tables which are hashed.

    Kind Regards,

    Andrew.

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