Re: gEDA-user: Spice netlister

[John Doty <jpd@xxxxxxxxxxxxx>]

On Jan 20, 2008, at 6:51 AM, a r wrote:

> I have looked closer into the sources and into the "RF_Amp" example  
> circuit.
>
> If a "spice-subcircuit-LL" component is added to the schematic the
> netlister will wrap it up with a .subckt/.ends cards. That's pretty
> close to the behaviour I wanted. There are some issues, though:
> 1. It forces me to add a simulation card to the schematic. In general
> cases that something I'd like to avoid (it is OK for testbench
> schematics, though).

I don't see why that's a big deal.

> 2. All nested models or ".include" cards (if "-I" option was used) are
> added inside the .subckt. That may cause problems with spice
> simulators that do not like such nested constructs.

Indeed, that's an annoyance, not only for simulation but for layout.  
The layout contractor I work with wants to see each cell in the  
netlist exactly once, at top level, not nested. But a little  
postprocessing gets the job done here.

> 3. There are special "spice-subcircuit-IO" components used for making
> subcircuit pins. Does it mean the netlister cannot cope with "normal"
> instance pins?

There are a couple of different ways to do hierarchy. If you use  
source= to associate the symbol to its subcircuit, you use the  
symbols in the "io" library to make your connections in the  
subcircuit schematic. In this case, the netlister expands all  
hierarchy automatically, making a flat netlist.

On the other hand, if you use the model-name= attribute to make the  
association, you need to use the spice-subcircuit-IO symbols in the  
subcircuit schematic. In this case, you won't get a flat netlist, but  
if you also use the file= attribute you'll get a nested hierarchical  
netlist, which I don't find terribly useful.

One of the difficulties is that SPICE pin associations are by pin  
order (pinseq=), not by name. If you're importing a macromodel or  
cell from outside the gEDA world, you won't even have a subcircuit  
schematic.

It would be nice to be able to suppress the automatic netlist  
flattening that gnetlist does, giving the back end the option of  
creating a hierarchical netlist in the source= case.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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