Re: gEDA-dev: some suggestions

[Stuart Brorson <sdb-at-NOSPAMcloud9_dot_net>]

On Thu, 14 Dec 2006, Peter TB Brett wrote:

> On Thursday 14 December 2006 18:20, Stuart Brorson wrote:
>
>
>> Better to add hierarchy to gschem and gnetlist, IMO!
>
> I'm currently using heirachy in gschem and gnetlist in the design of a rather
> complex circuit board... so I'd describe that as a fait accompli.
>
> Unless you meant something different, of course.

I'll bet you don't use any busses, and your netnames are all global.

Hierarchical busses remain a problem for gEDA.  That is, I can't just
connect a bus called foo[7:0] to a pin on a block, and have all the
nets in foo[7:0] show up at the lower level.  Pins are strictly
single-net constructions as gEDA currently stands.

As for other types of hierarchy, a big problem arises if you have one
top-level block, and in it you want to instantiate multiple identical
copies of a lower-level block.  This is common in IC design, but I
have also done such a thing in a 4 port IO PCB I did once.  Each
lower-level block is identical, but must have different refdeses and
different netnames on the lower level so that the different nets
aren't all shorted out in the resulting netlist.  Acceptable netnames
can be of the type foo1_upper:bar_lower, foo2_upper:bar_lower, etc.
Acceptable refdeses might be U1:U5, U2:U5 and so on [1].  Doing this
is a problem for both gschem and for gnetlist.

Unless things have changed in the last few months, gEDA can't handle
these issues.  If I'm wrong, please tell me!

Stuart


[1]  Then these refdeses are changed at layout time to something more
sensible like U5, U6, etc, and backannoed into the schematic.
(Good -- actually any -- backanno is the other important missing piece
in gEDA.)  Doing this in a hierarchical design in not trivial, and is
prone to error. ViewLogic does something they call OATS, which is some
scheme to overwrite lower-level refdeses from the top level.  It
always broke for me, but I probably didn't understand it.


_______________________________________________
geda-dev mailing list
geda-dev@moria.seul.org
http://www.seul.org/cgi-bin/mailman/listinfo/geda-dev