gEDA: some observations/experiences with geda as a simulation frontend

[mcmahill-at-NOSPAMmtl_dot_mit_dot_edu]

Inspired by Stuarts recent work on the spice backend for gnetlist, I wrote
a switcap backend and created a set of symbols for it.  This experience
has brought out a few items of note which can be a bit of a pain in using
geda for driving simulations.  They are (in no particular order):


- some simulators like switcap have restrictions on node name length.
  With switcap, this is 7 characters which makes 'unnamed_net37' not work. 
  It wouldn't suprise me if some other simulator somewhere doesn't like
  nodes to have anything other than numbers.

- it would be quite nice to be able to have the schematic show the
  netnames without having to manually name them all.  The reason for this,
  is you might do a spice simulation and then decide you want to plot 
  some node which you didn't explicitly name.  In the current approach,
  you're pretty much stuck since nets without explicit names don't get
  named until gnetlist is run.

- is there a way in the gnetlistrc to specify a search path for scheme
  files?  I just copied all the share/gEDA/scheme/* files to a local
  directory and used the (scheme-directory) function to point there while
  working on gnet-switcap.scm.  It might be nice to have a search path
  which included multiple directories.

- this last one is probably a much bigger task, but it might be nice to be
  able to use scheme to create some sort of GUI for setting up analyses.
  I've been trying to finish up the switcap support by adding some symbols
  which will cause an analysis statement in the netlist.  The problem is
  its a bit cumbersome to deal with all the possible options you might
  want.  For the current system, I'll probably just have an include file
  element where you can have it insert a text file with the analysis
  commands.


All in all though, it was pretty easy and pretty quick to produce a
working backend (which I will post here after a little more testing and
verification).

-Dan