gEDA-dev: [PATCH] GAF: Solve the "transistor problem"

[Bernd Jendrissek]

Hope the signature survives gmail pasting...

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This patch solves the "transistor problem".  AKA logic gate and op-amp
problem.  For those unaware, the problem is: just count the number of
distinct op-amp symbols.  Yet they're all op-amps!  Same with transistors and
logic gates.  The trouble is that once you have chosen a part to put into your
schematic, it takes effort to change to another part later.  You'll have to
delete the existing symbol (don't forget to check for any attributes you may
have attached!) and insert a new one in its place.  You'll have to check that
its pins are equivalent to those of the old symbol.  Once you're satisfied,
you have to translate and rotate the new symbol into the same position as the
old one was, and then hope that the pins still line up with the nets that were
there.

The solution is to capture your schematic with only "abstract" symbols:
symbols that provide only the graphical representation of a function.  You may
have abstract symbols for BJTs, op-amps, logic gates, resistors, capacitors,
memories, etc.  You will connect your nets to the pins on these abstract
symbols.  You will NOT have abstract symbols for specific parts, like an
LM324A or a 74LS00.  Specific parts will be on your schematic as "slotted
components".  Their only purpose is to provide slots for abstract symbols, so
that your abstract symbols can inherit attributes like refdes=U100, and that
your abstract symbols' pins can be numbered properly according to the part.

I implemented the solution by introducing a new member ->owning_slot to struct
st_object, which points to the slotted component to which an abstract symbol
is currently assigned.  The other side of this slot assignment is inside
struct st_complex: its ->prim_objs list can now also contain OBJ_SLOT objects,
whose slotmap=<pinseq1>=<pinnumber1>,<pinseq2>=<pinnumber2>,... attributes
provide the pinseq-to-pinnumber translation (*).

If a selected symbol has a slotname=<anything> attribute, gschem will know
that the symbol is "abstract", and will open the "slot chooser" dialog which
will let you select an available slot to which you can assign the symbol.  The
dialog has toggle buttons which let you control the safety checks that the
dialog makes: by default it won't let you assign a symbol to a slot if the
symbol and the slotted component have conflicting attributes.  This lets you
assign only op-amp symbols to the op-amp slots of an LM324A, or only nand gate
symbols to the gate slots of a 74LS00.  You can force the dialog to let you
choose slots with conflicting attributes, by disabling the "Compatible"
button.  The "Hijack" button (off by default) lets you select slots which are
already occupied by other abstract symbols.

(*) Currently the translation is to "die pin number", which refers to a
specific pad on a piece of silicon.  I hope soon to add the second mapping
from "die pin" to "package pin", to account for the differences in pin
numbering standards for different package types.  (A QFP and a PLCC may have
identical chips inside them, but their pin numbering is different.)  I'll
probably do this by introducing another OBJECT type OBJ_PART that will be a
container for part-specific attributes such as this second (die pin to package
pin) mapping.  Footprint attributes would also be a good use of this.

This patch is against gaf.git-19b6b06461a906399126803d4c46a5a42d1cc784.tar.gz
You can find the ChangeLog entries by searching for ^CHANGELOG.  Following
each CHANGELOG for a subdirectory of gaf.git/ is a patch covering only that
subdirectory.

ab64506c1dbffba02487e06f29d356d94367ae2b
gaf.git-20070806-abstract-symbols.diff.bz2
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