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Date: Mon, 31 Aug 2015 09:52:17 -0400
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Subject: Re: [geda-user] back annotation proposal (RFC)
From: "Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
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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 If the information in pcb is no longer valid for the device (i.e. you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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