Mail Archives: geda-user/2015/10/24/01:28:11
> There are multiple angles to this problem.
> - the gschem end
> - the rendition of this semantics in (one of many) netlist formats
> - the treatment of that netlist information in board layout (or other hardware)
>
> At the gschem end, and the netlist representation, I don't see any
> sensible approach besides having a symbol and a component.
Perhaps gschem needs a separate "star point" construct. For example,
a large dot you can place, and any nets that connect at that dot are
considered "connected but separate". No need for custom symbols or
pre-guessing pin counts.
As for the netlisters, they'd each have to do what their downstreams
expect. Internally, we could have netlisters that know about star
points to call a guile function that enables them and disables
warnings about multi-named nets.
> On to PCB (or any other layout too; John Doty can close his ears for
> this part). AFAICT, there is no established technique to implement
> such a star short in a way that will pass DRC. There needs to be
> copper half-inside the DRC process, that definitely shows up on the
> Gerber output. This copper can't exist during the netlist check
> (optimize rats).
<[Blue skying> We've talked about being able to "label" copper with
net names, for example labelling a polygon with "net=GND" to override
what DRC and rats guess at. We could allow labelling copper with
"net=GND,AGND" or something, to say that it may be connected to
multiple nets. That would allow us to use a line, arc, polygon, via,
pin, etc as the "star point". Such labels might also help with short
detection, by limiting where DRC might guess a short would be.
Of course, anything like this would predicate a new DRC :-(
A label of "net=<ignore>" could be used for antennas etc, although if
we had true copper-in-footprint we might need to rethink how to tell
"copper that's a net" (like tying two gnd pins together) from "copper
that's not a net" (like an antenna).
</Blue skying>
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