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Re: gnet-PCB.scm patch [was: gEDA: another gnet-drc2.scm patch]

Carlos Nieves Ãnega wrote: 
Hi Dan,

El jue, 02-03-2006 a las 16:09 -0500, Dan McMahill escribiÃ:
[snip]

I'm generally opposed to using "special" netnames. I've managed to jump in here late in the discussion, but it seems to me that you shouldn't be connecting your schematic up as a short.

Don't forget, you have 26 other backends besides the PCB backend.

Was this just to keep drc2 from complaining about unconnected pins?

If so, perhaps we can come up with a better no connect symbol which doesn't use a fixed net name. 


If you have unconnected pins and you don't use the DRC, it's all ok. If
you want to use the DRC, you should have some way to tell it that you
really want to leave a pin unconnected.
I've seen several approaches to this:

- Use a special no connect symbol. Currently there is such symbol in
gschem, which connects that pin to a net named "NoConnection". 

  - Another approach here would be that gnetlist don't add that pin to
the netlist (it can know it is a special symbol), but then the DRC won't
be able to check it.


  - I've also seen some DRC markers so the DRC don't check a given net,
but this situation would be like the previous options.

Clearly if you're driving a spice simulation you want the net to be given a unique name and have it show up in the netlist even if it doesn't connect anywhere else. For example, you may have a subcircuit where you're not connecting anything to one of the outputs but you want to be able to plot the signal there.

In fact, right now if you use this no connect symbol, you'll actually short out everything in the spice netlist too unless thats also updated.

I suppose the problem is if we simply get rid of the net connection in the no connect symbol, we'll have a problem where various backends will try to netlist it.

What would be nice is if attaching a no connect symbol could attach an attribute to the net to indicate that a single connection is ok but otherwise act as a graphical symbol which is ignored globally by gnetlist. Then other backends won't have problems and drc2 can key off of a net attribute.

-Dan