Re: gEDA-user: wishful UI

[Stefan Salewski <mail@xxxxxxxxxxxx>]

On Mon, 2010-08-16 at 12:00 -0400, Rick Collins wrote:

> >
> >I think we should try to find a better name for the connection between
> >two nodes in a net, maybe segment?
> 
> In the layout program I use, a segment is a single section of a PWB 
> route between two points.  That is, it is the shortest specified 
> portion of a route.  The entire connected entity is a net and a 
> connection between two pins or a T vertex is a trace.  The trace is 
> equivalent to what you are trying to describe.
> 

True, segment was a bad propose from me. I am not sure if trace is
really good, in my mind trace is bound to a special shape...
Maybe we should simple say "connection between two points/pins/nodes.
(I still wonder about the term PWB, a google search does not really
help.)

> A lot of the discussion in this list is conducted as if the 
> functioning of schematics were the only consideration.  Why not start 
> with what you are trying to do in the layout, consider what the 
> layout tool needs to make that happen, then trace that back to what 
> is needed in the schematic to support the layout?

Indeed, that is what I would do, if I would be alone...
Please note, I was not the one who has the "idea" of specifying
attributes on the schematic level. This discussion is really old, at
least it existed when Anthony Blake starts with his topological router
and we consider how to make that router more smart. And as Kai-Martin
told us, this concept is in Protel for ten years. So it is not an idea
at all, it is an concept, and the question is, how useful it is. I wrote
that down, with a small picture, because my memory is not too good...
The whole story started this time with ideas  of Andrew Poelstra, and it
may start again in a few months...

> So much of this 
> conversation just seems so disconnected from what might be needed to 
> do real work.
> 

This is true -- from time to time we have discussions from new users
with great ideas and wishes, but without the skills and time to program
that. Sometimes I am one of them.

> If you want to consider impedance, then lets start with the ways you 
> would want to control impedance and figure out just what that demands 
> of layout and then the schematic?  Normally when I am controlling 
> impedance, I am using point to point connections with no branches or 
> stubs.

Sure, this is the general and most important case.

>  But if they are kept short, a stub can be used with impedance 
> controlled nets.  Likewise, I seldom have more than one receiver on 
> an impedance controlled nets, but I can see where a bus might need to 
> be impedance controlled even with many drivers and receivers.  So it 
> seems like in layout you would need impedance on an entire net, not 
> just a trace or subnet.  When would you want a layout to control 
> impedance on a portion of a net and not the entire net?
> 
> Rick 
> 

I do not really like to discuss all that details now. When we build a
new house, it is difficult to predict the final color of the inner
rooms. Indeed I think that a net with defined impedance should define
that impedance to the whole net, no need for subnets. But I may be
wrong. One special case is the example which I mentioned yesterday, when
we want to enforce a special shape of a net in the schematic level. But
for power supply nets, different attributes for different traces of a
net makes sense, and most devices need power supply.

Best regards,

Stefan Salewski




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