gEDA-dev: RFC: gnetlist uref mangling (WAS: Re: Broken slotting)

[Peter Clifton <pcjc2-at-NOSPAMcam_dot_ac_dot_uk>]

On Thu, 2007-09-13 at 06:40 -0400, Stuart Brorson wrote:
> > Can you post an example of how a complex component's pins and their pin
> > numbers would be arranged to satisfy spice?
> 
> Steve --
> 
> There is an example in the regression test suite which might answer
> your question.  Look at the source under:
> 
> Input schematic:
> ${SOURCE}/gnetlist/tests/spice-sdb/outputs/SlottedOpamps.sch
> 
> Output netlist:
> ${SOURCE}/gnetlist/tests/spice-sdb/outputs/SlottedOpamps-output.net
> 
> Does this clarify the intended behavior?
> 
> Stuart

I think we're looking at a different problem here - that is; we have 4
symbols instantiated, all with refdes=U1, and the spice-sdb backend
wants to treat them as individual entities.

gnetlist (whilst keeping them separate in its NETLIST structure), refers
to them by a common refdes U1 - and its not possible to separate them.

A similar problem exists when using the gschem->PCB workflow, where
sometimes people (like I used to) like to name slotted parts IC1a IC1b
IC1c etc...  PCB doesn't care about the lower-case suffix, treating all
the above as if they were "IC1". gnetlist treats them separately of
course, and gsch2pcb outputs multiple footprints with the wrong refdes
in this case.

Do we want to allow both of the above behaviours?

If so, it seems that we might want some per netlist-backend control of
how gnetlist processes refdes.

I think this mapping could be implemented as guile a callback function
to the gnetlist backend to allow it to return a refdes for each
component parsed in the schematic - to place in the NETLIST structure
for that component.

It would do this with full access to that component's attributes, and a
default implementation should just copy the refdes= attribute (to get
the current behaviour).

The gsch2pcb backend might introduce the mapping from IC1[a-z]* to IC1.
Any refdes which exit this mapping with the same string would be emitted
as a unique package thanks to g_get_packages() not repeating duplicate
refdes'.

The spice-sdb backend mapping may wish to consider any slot= attributes
(and other attributes which indicate the presence of slotting), to
transform refdes=IC1; slot=n -> IC1.n (and so on). This would give each
slot of a component a unique uref with which to identify pins and
connected nets.

I'm not 100% sure how this fits with hierarchical uref mangling, however
this isn't likely to be an insurmountable problem 


Any comments?

Regards,

Peter C.




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