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	Mon, 31 Aug 2015 07:16:42 -0700 (PDT)
Date:	Mon, 31 Aug 2015 16:16:36 +0200
From:	"Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
To:	geda-user AT delorie DOT com
Subject:	Re: [geda-user] back annotation proposal (RFC)
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It is not enough doing the same thing as gnetlist but in reverse is not enough. Changes may come from any direction so it is also necessary to know in which directions change should be made. If footprints are different should there be a forward or backward annotation? If there are unsaved changes?



On Mon, 31 Aug 2015 09:52:17 -0400
"Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com> wrote:

> On Mon, Aug 31, 2015 at 3:41 AM, DJ Delorie <dj AT delorie DOT com> wrote:
> >
> >> That makes a lot of sense for the netlist but what if you change a
> >> footprint? I think there should be another tool that you run in
> >> parallel to gnetlist to handle that.
> >
> > I assume a much more intelligent netlister.
> >
> > The netlister maps what it knows about each symbol to a list of
> > candidate options for "heavifiing" the symbol into a full component.
> > One of these options is the package, and once you somehow choose a
> > package, there's one or more footprints that go with it.
> 
> See to me that is 2 different tools
> 1. To handle migration of the netlist into gschem (I think more of
> this might happen in gschem than Igor2 expects right now but I have to
> sleep on my ideas before saying more)
> 2. To handle changes in symbols and their properties (footprint and etc)
> 
> Tool #1 is doing the same thing as gnetlist but in reverse
> implementing something like minicut from pcb-rnd. I think that is at
> least a fork if not a whole other tool from gnetlist.
> 
> > Part of my idea is that pcb takes all the choices it knows about and
> > gives them to the netlister, so that the netlister can use that to
> > narrow down the options it's left with after dealing with the
> > constraints in the symbol.
> >
> > I.e. if you have a generic AND gate symbol, there's lot of options for
> > the netlister.  But if this is a future iteration, pcb might already
> > know that you picked a 74ALS00 in a SDIP-14 package with the SDIP14M
> > footprint.  It can tell the netlister this when it does an
> > update-import.  It can also tell the netlister what pin mappings were
> > used.
> >
> > If the information in pcb is no longer valid for the device (i.e. you
> > changed a 2-in AND to a 3-in AND), then the netlister would discard
> > pcb's choices and start fresh.
> 
> I have to think about this more. A lot of stuff (like slots in
> symbols) only works for things like 7400 series logic.
> 
> > So, there's a lot of back-annotation information being sent from pcb
> > to the netlister, which lets you do package, gate, and pin swapping in
> > pcb, but none of it ends up back in gschem unless you do something
> > specific to make that happen.

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