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Re: gEDA-user: Subnets



At 04:27 PM 8/15/2010, you wrote:
On Sun, 2010-08-15 at 15:43 -0400, Rick Collins wrote:
>
> First, I want to say that power supply bypassing is probably not a
> good example to use since there are a number of ways to layout such
> things and many people will disagree about the "optimal" way of doing
> it.  Perhaps a more general example can be used?
>
No. The basic idea of our proposal was to define attributes/classes for
nets in the schematic. Subnets are only a special case, which makes much
sense in the case of power supply. OK, one more, but very special case,
where subnets may be useful: We can have nets of 3 nodes, where we want
a linear shape, not a T or star shape. For this case we may define one
subnet from pin 1 to 2, and one more from 2 to 3. We make these two
subnets not compatible, so they are allowed to touch only at pin 2. So
we can enforce the shape of the layout on the schematic level.

> You are talking about everything in the context of what you would
> like to see in the schematic editor.  But none of this is useful
> unless the autorouter handles it.

No. It would be fine if the autorouter can access this information. But
all these attributes/classes are a great benefit for manually routing.

For details see the related posting in this list...

Maybe you are missing my point. What value does the subnet have if the layout TOOL doesn't know about it? What do the routing tools know at this point? If the answer is nothing, then why push from the schematic end? Wouldn't it make more sense to push from the layout end? Then add to the schematic program what is needed to support the layout.

I've never heard of a layout tool that knew anything about subnets. Why invent something that can't be used with the layout tool? The other attributes are fine. Trace width, max length, etc. But how do you convey that info to an arbitrary layout tool? Is there a netlist format that supports such extra info?

This pie-in-the-sky stuff is fine, but I can see much more utility coming from more mundane developments.

Rick


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