gEDA-dev: Thoughts on buses in gschem

[Dan McMahill]

Steve Meier wrote:
> Peter,
> 
> I am very interested in hierarchical bus structures. A lot of what I am
> going to say is probably obvious.
> 
> Buses should be capable of grouping a large number of nets together.
> Busrippers are used to join nets to buses. The question is which
> position within a bus the joined net connects to?
> 
> I agree there needs to be some method for organizing the nets within a
> bus and then for the busripper to selectively attach to one of the bus
> contained nets.

I guess I'm not a big fan of needing to have a special busripper or a 
special 'bus wire'.  I think they're both somewhat redundant although I 
can perhaps be convinced otherwise.

The way cadence handles it is all wires are basically equal and if 
they're fat (like for a bus) or thin (like for a wire), its strictly for 
appearance.  They way a wire becomes a bus is by labeling it or by 
connecting to a pin which is a bus by virtue of it carrying more than 1 
signal.

bus ripping is done simply by connecting up a wire to the bus and 
putting the right name on it.

There are a few extra constructs which can be most useful.  One of them 
is the ability to repeat signals on a bus.  "<*n>A" would give you "n" 
copies of the "A" signal.  Also iterated instances of symbols is a 
useful thing.

I'm attaching a screen plot of a few useful bus type constructs.

Again, note that a line being narrow or wide is simply an option I set 
and is graphical only.

-Dan
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