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Date: Wed, 21 Oct 2015 19:30:02 -0700
From: Larry Doolittle <ldoolitt AT recycle DOT lbl DOT gov>
To: "Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Subject: Re: [geda-user] A lesson from gnet-makefile
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Guys -0

On Thu, Oct 22, 2015 at 02:03:43AM +0000, Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com] wrote:
> On Thu, Oct 22, 2015 at 1:49 AM, DJ Delorie <dj AT delorie DOT com> wrote:
> > It would be great if you could just connect two
> > nets like that and have the system remember the topology long enough
> > to DTRT in layout.  But in gEDA, this type of connection only results
> > in an error.
> 
> Well I was approaching that with the stuff I was talking about in the
> other thread but I realized there were fundamental issues with it.
> This is kind of why I was thinking about star grounds. Really this is
> a type of star topology.

I don't think this failing is unique to gEDA.  I just had a
board laid out in PADS (schematic in gschem), and some analog
stuff had to be left hand-wired, non-design-rule-checked, because
of this exact issue.  Just like in PCB, there seemed to be no way
to communicate to the layout tool that two nets are supposed to
touch in a defined spot, but be independent.

I think it's easy enough to create a "star" component in gschem;
getting a layout tool to deal with it seems harder.  I've heard
of hacks involving extra layers to make it happen in PCB.  The
team of PADS experts (not sure if a smiley face belongs there or
not) couldn't even imagine a way to make it happen for that tool.
Other than adding a bunch of zero Ohm resistors, which I rejected.

  - Larry