Re: gEDA-user: Multiple footprint methodology?

[DJ Delorie <dj@xxxxxxxxxxx>]

> 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.

> 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.

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.


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