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From: John Doty <jpd AT noqsi DOT com>
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Subject: [geda-user] A lesson from gnet-makefile
Date: Mon, 12 Oct 2015 12:25:40 -0600
Message-Id: <1042003D-82E2-40F0-AB60-8186580C46AD@noqsi.com>
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Folks,

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?

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.

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.

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.

Of course, we=92d need a layout program that could accept this info.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com



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