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Re: gEDA-user: PCB object data and attributes

On Jan 3, 2011, at 3:33 AM, Stephan Boettcher wrote:

> John Griessen <john@xxxxxxxxxxxxxx> writes:
>> On 01/02/2011 04:14 PM, Stephan Boettcher wrote:
>>>  If you do not use it, why do you care about associating
>>> netnames to traces?
>> That's not about auto DRC enforce drawing, it's about searching
>> for parts related to schematic and cross probing
>> and creating layout dereived models of trace capacitance
>> for simulations.
> All of this should depend on the actual copper connectivity, not on some
> (invisible) attributes of drawing elements.

Yes. the netname belongs to a different level of abstraction, where geometry is assumed not to matter. Only topology matters. And while one can talk about the capacitance between nets, one generally cannot deal with inductance and resistance in this manner.

I am increasingly seeing fast digital chips that are designed to be connected by transmission lines, not nets. Right now, every layout person I know pretends that transmission lines are composed of nets, and then manually forces their tool to create a transmission line geometry.

As this gets more common, I expect that it will be important that the tools be capable of more automation in this area. gschem is in good shape here, as it does not make any semantic assumptions about its "nets", at least if you turn off net consolidation. "nets" in gschem therefore can easily represent transmission lines (or busses, as Paul Tan has shown). gnetlist isn't so flexible, as it hides the geometry, revealing only topology, and also hides attributes attached to "nets".

John Doty              Noqsi Aerospace, Ltd.

This message contains technical discussion involving difficult issues. No personal disrespect or malice is intended. If you perceive such, your perception is simply wrong. I'm a busy person, and in my business "go along to get along" causes mission failures and sometimes kills people, so I tend to be a bit blunt.

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