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Subject: Re: [geda-user] Net attributes
From: John Doty <jpd AT noqsi DOT com>
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Date: Thu, 16 Jul 2015 15:45:18 -0600
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On Jul 16, 2015, at 3:23 PM, DJ Delorie <dj AT delorie DOT com> wrote:

> 
>> Nope. I sometimes have to make multiple copies of a subcircuit
>> schematic: same topology but different components. Having more
>> control over hierarchy expansion in gnetlist would be good.
> 
> I was thinking about the m4 problem in pcb and thought "I wonder if we
> could put a generic expression parser in where we expect simple
> values".  I don't think it would help much for pcb (without a looping
> construct, at least), but it might help for heirarchical schematics if
> a component could have a value that was an expression referencing
> inherited attributes from the parent.

Inherited attributes would be nice. Needs a new mechanism in code few understand, though.

>  The schematic flattener (if
> you're flattening it for netlisting, for example) would expand the
> expression.
> 
> Part of me says "put a guile expression there" but that opens up the
> problem of having a schematic with executable code in it.

I’ve considered, for similar purposes, making a tiny recursive top-down interpreter for ordinary arithmetic expressions in Guile. Such things are not difficult to write. That would keep the executable code genie in the bottle.

>  Given the
> nature of electronics, a mathematical (TeX? Mathematica?) expression
> would be more natural, but bring its own can of worms…
> 

If you’re specifying discrete part values, one tricky issue is specifying the catalog of acceptable values.


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