Mail Archives: geda-user/2015/10/12/17:58:50
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On Oct 12, 2015, at 2:06 PM, Nicklas Karlsson =
(nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com] =
<geda-user AT delorie DOT com> wrote:
>> Folks,
>>=20
>> I had thought that the lack of a way to access attributes other than =
netname=3D on a net via gnetlist was a serious barrier to the back end =
writer. However, for gnet-makefile.scm I find myself using the =
attributes of the attached symbols as a rich source of information about =
the net. Is this perhaps the best approach anyway?
>>=20
>> Nets in a schematic represent collapsed topology, not geometry or =
even the complete topology. The layout system is responsible for these =
things. A schematic doesn=92t capture the relationships between the net =
segments. Some paths on a net may carry large currents, but others may =
not. Pairs of nets may represent balanced transmission lines.
>>=20
>> But, suppose instead that we had a pin attribute that said =93this =
pin may draw three amps=94. The netlister could then deduce which paths =
on a net need extra conductor.
>>=20
>> Suppose a resistor had an attribute that meant =93100 ohm shunt =
terminator=94. Imagine a component with a pair of pins identified by an =
attribute as a differential input. Put them on the same pair of nets, =
and the netlister could deduce that the pair is a balanced transmission =
line and the the resistor needs to be close to the input.
>>=20
>> Of course, we=92d need a layout program that could accept this info.
>>=20
>> John Doty Noqsi Aerospace, Ltd.
>> http://www.noqsi.com/
>> jpd AT noqsi DOT com
>=20
> As I understand it you want to assign attributes to pins instead of =
nets.
>=20
> A net is only allowed to have one driver and will get the voltage of =
the driving pin and from this voltage a suitable clearance may be =
selected. For current it will be the other ends.
Seems rather rigid. Some circuits are like that, others not so much. But =
it=92s a good first approximation, better than anything we have.
> It might work but I still think net names are useful sometimes, maybe =
it would be useful to use the driving pin to assign the net name, if =
this is simple to implement I guess it would be worth a try.
You can do that with the net=3D attribute on a symbol, if you like. I =
don=92t see anything new or special about the net name. The other things =
you can learn about it by looking at what it=92s attached to interest =
me.
>=20
John Doty Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com
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