gEDA-user: Multiple footprint methodology?

[Dave N6NZ]

DJ Delorie wrote:
>> Given a part with two or more packages, how should the footprint
>> mapping be defined in the symbol?
> 
> It's not, it's added later through, for example, gattrib.

Yes, I get that.  I asked my question poorly. There is an attribute in 
the symbol that points to the correct pin mapping. I get the concept, 
but I don't know where all the ascii lives, and how it should be split 
up across various files.

> 
>> In the case of the ATMega88, the TQFP-32 version of the part brings
>> out more I/O than the PDIP-28 version. Soo... choices. 1) Define all
>> the pins, but don't map them to PDIP-28?  Will net lister issue
>> warnings? 2) different symbol?  Icky, because you would like to
>> switch packages without deleting/inserting a symbol.
> 
> If it were me, I'd have multiple symbols - one common one for the
> common pins, and a set of alternates for the I/O areas that change.
> As long as they have the same refdes, the netlister knows how to deal
> with them.

Perfect!  Naming convention?  PART-1, PART-2?  Or PART-1, PART-EXTRA-1?

Is there a way to make the "extra" pins have a default tie-off so that 
you don't need to add the extra symbol in designs that don't use those 
pins?

> 
> I did this for the m32c, which has a "cpu" side and an "I/O" side.
> Also for an ethernet chip; one symbol for the cpu side, one for the
> network side.  That also lets you put the different sides on different
> pages.
> 
>> ATMega88 is actually one of a family of 3 parts: ATMega48, ATMega88,
>> ATMega168 which have identical pin-outs but different sizes of
>> internal memory. Again, if you have a board designed around an
>> ATMega48 and go "oooooops -- code bloat -- need an ATMega88", then
>> it would be nice to be able to flip an attribute and get a new BOM.
> 
> You just edit the footprint attribute.  We just don't expect the
> symbols to "just know" which footprints go with it; this is the common
> heavy vs light symbol debate.  We chose light, which means the symbols
> know little about how they're going to be used, and you use something
> like gattrib to set all the footprints.
> 

That's not my question -- this is the flip side of "same symbol with 
multiple footprints".  This is different BOM callout, but same footprint 
and same schematic symbol (other than BOM part number).  If I name the 
symbol "ATMEGAx8", can the user simply edit the attribute after 
insertion and not screw up the downstream tools and any library references?

-dave