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Subject: Re: [geda-user] Possible paths of gnetlist development
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From: John Doty <jpd AT noqsi DOT com>
In-Reply-To: <20160926102647.1820967e@floyd.freeelectron.net>
Date: Tue, 27 Sep 2016 09:54:27 -0400
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On Sep 26, 2016, at 10:26 AM, al davis <ad252 AT freeelectron DOT net> wrote:

> On Mon, 26 Sep 2016 09:05:21 -0400
> John Doty <jpd AT noqsi DOT com> wrote:
>> 1. Use attributes for rather than special backend-dependent symbols
>> like spice-subcircuit-LL.
>=20
> I agree.
>=20
> Likewise, backends should not have anything symbol-specific.

There=92s nothing symbol-specific in gnetlist. A back end can=92t even =
find out which symbol(s) a =93package=94 corresponds to. But =
spice-subcircuit-LL.sym has the attribute device=3Dspice-subcircuit-LL, =
which the SPICE back ends recognize. The problem here is that the layout =
back ends think this is an actual component.

>=20
> and all backends should support attributes, in a consistent way.
>=20

The trouble here is that gEDA supports an open-ended variety of flows, =
and one size does not fit all. Every gnetlist back end uses the =
footprint attribute, but what should you put in it? The names from your =
layout tool=92s library? The gEDA convention =
(http://wiki.geda-project.org/geda:pcb_footprint_naming_conventions, =
mischievously presented as a pcb convention)? If you use the gEDA =
convention, do you alias the footprints in the library to match, or do =
you automatically translate? A lot depends on the size of the project, =
the tools employed, and the skills and preferences of the designer(s). =
I=92ve used every one of these approaches for one project or another.

If you=92re simulating with SPICE, you=92ll want your numeric value =
attributes to be SPICE numbers. Fortunately, procurement folks find this =
usable in a BOM. But for a different flow, you might want something =
different.

Then, there are attributes for specific back ends. Some of the standard =
library symbols have pins and class attributes for Allegro. The class =
attribute is probably not useful for any other flow, but I find pins =
useful for DRC =
(http://www.gedasymbols.org/user/john_doty/tools/check-pincount.html).


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



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