Re: gEDA-user: Driving the netlist from PCB (instead of gschem)

[Rick Collins <erudite999@xxxxxxxxx>]

At 07:06 PM 9/28/2008, you wrote:

> > I guess I am thinking in terms of having partially routed a net and
> > found that to continue, it is better to swap a pin at the unrouted
> > end. Are you saying that you can see the problem without routing?
>
>Yes, sometimes.  For example, running 24 chip select lines out to
>drivers, you can look at an unrouted rats nest and decide what needs
>swapping.
>
> > If you just update the schematic and import the new net list,
> > doesn't that cause the trace for that net to be ripped up?
>
>It doesn't rip it up, but it does show up as a short.

And how is that then fixed?


> > Sure, you can say it's a waste, but wasted what, disk space?
>
>Support in the applications for data and syntax they won't be using.

I don't follow.  The "syntax support" is just to ignore the entire 
section that does not apply to schematic or whatever part is being 
considered.  That doesn't strike me as a lot of overhead.


> > If a format such as XML is adopted, then I think that has lots of
> > overhead, but likely without much impact really.
>
>We've discussed XML before, and chose not to use it due to the uneeded
>complexity.  Some other structured text format may be used though.

What "uneeded complexity"?  The idea that the internal and external 
format could be the same seems much simpler than to store in one 
format and then have to convert to the other... of course this is 
assuming that the IPC standard becomes adopted by industry.

Standards may not always be optimal for any given application.  In 
fact, they are pretty much assured to *not* be optimal since they are 
often compromises.  But there is a huge advantage to being 
"standard".  Of course, I am sure that Gerber formats will not go 
away overnight.  I just see a significant advantage to being able to 
share the data file between apps without having to convert and output 
special files, such as "back annotation" files.

 From what I have seen, EDA support for the electronics fabrication 
industry is some 15 years behind the times.  This sort of file format 
is exactly the sort of thing that needs to be brought into the 21st century.


> > it appears that every open source layout and schematic tool has to
> > reinvent the file format wheel.
>
>We don't *have* to.  We *choose* to.  Each designer has different
>functionality they're trying to encapsulate, and come at it from a
>different direction.  That drives the choices.

That is what I meant by "has to".  File formats don't really need to 
be optimized for most applications.  Often people optimize things 
that are not really needed because that is what they do.  They don't 
do it because it is required by the app, but because it seems like it 
is a good idea.  Uneeded optimization is the bane of flexible, 
effective design.  I've seen papers written on this.  



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