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Date: Mon, 14 Sep 2015 12:34:17 +0200
From: "Gabriel Paubert (paubert AT iram DOT es) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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Subject: Re: [geda-user] RFC: pin attribute remapping
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On Sun, Sep 13, 2015 at 06:09:05PM -0400, DJ Delorie wrote:
> 
> > > Aside from assigning GUIDs to each symbol as they're instantiated, I
> > > don't have a good solution to this.
> > 
> > The refdes assigned in the schematic is the GUID, just as
> > always. Similarly, the pin number assigned in the symbol, after
> > translation via the slot number assigned in the schematic, is the
> > pin's GUID. Those don't change, but what the user sees in the
> > graphics might.
> 
> If you have a 7400, you already have four gates (and thus four
> symbols) with the same refdes. It's already not a GUID (globally
> unique identifer) because it's not even unique within the page,
> because saying "U4" doesn't tell you which of those four symbols
> you're referring to.  Saying "the U4 that had pin 2" might work,
> unless we do away with numberic pins in favor of symbolic ones, then
> all four gates have pins A,B,Y - not unique either.  With a symbolic
> light symbol like that, pin and gate assignment might happen much
> later, so device "U4" on the layout might include gates from U3, U7,
> U5, and U14.  If you want to do an as-built of that, you need to know
> *which* U3 symbol, *which* U7 symbol, etc.
> 
> The only way to let the refdes be a UID (much less a GUID) is to
> enforce it in gschem and gnetlist - a hard error if you reuse one -
> and assume that slotting is going to make a new, probably messy,
> refdes in the layout.  And that just makes the power pin problem
> worse, plus stops people from splitting a large chip into mutltiple
> symbols.

Which is a big no-no. It's plain impossible to use a single symbol for a
chip with hundreds of pins.

    Gabriel