Re: gEDA: python frontend for ngspice

[Cyril Giraudon <cyril_dot_giraudon-at-NOSPAMfree_dot_fr>]

al davis a écrit :
> On Wednesday 03 May 2006 12:07, Cyril Giraudon wrote:
>> Hello,
>>
>> I actually try to write a tclspice like tool in python
>> (pyrex, numpy modules).
>
> How about doing it for gnucap?
>
> Lots of people have written front-ends and wrappers for Spice.  Gnucap 
> really needs something like that, and to provide the functionality of 
> "nutmeg".
Hello,

My idea is to write an object oriented python module, and I need a 
python module for my work.

For instance I'd like to write :

import circuitModule as cm
cl[]
cl['c1'] = cm.Circuit('aFile.cir')
cl['c2'] = cm.Circuit('anOtherFie.cir')

for c in cl:
  c.run()

d = cm.Circuit('aThirdFile.cir')
e = d.run().toArray('V(1)')
# e is an array numpy.

The issue is not writing a pure spice frontend but rather a pythonic 
spice tool (module).
We can see the simulator has to handle several circuits at a time.
2 solution :
- The simulation can natively handle several circuits
- The simulation is already object oriented and one can instanciate more 
than one circuit : each circuit owns its namespace (matrices, results 
vectors)

I don't want to hack the simulator code (not too much), it's to hard to 
maintain.

I've tried to study and understand gnucap sources. Gnucap was the first 
simulator I thougth about : Pure C++ program, 8000 lines of code (I 
think), compiles very well.
Gnucap is written in C++ so I wished each circuit was a class instance 
with its proprieties and methods (own resolution matrices, ...) But it 
is not the way gnucap is coded, gnucap is not oriented "library". There 
are a lot of global variables that could be local to a simulation. So 
the only thing Gnucap permits is wrapping its interpreter and gives the 
capability to use gnucap inside the python interpreter (it's already a 
good thing).
Then I believe Gnucap doesn't save the nodes values when a simulation 
runs, Gnucap writes currents, tensions in a file or in the console but 
doesn't save them into the memory in order to retrieve them. So 
converting vectors into numpy arrays is not easy.

Spice is not written with an object oriented language but offers an 
"object oriented approach" : A struct instance for a circuit. All struct
instances references in ft_circuits... Nodes current and tension are 
stocked during the simulation. The conversion into numpy array needed 
only a 30 lines functions reusing native spice function.

So the job is not technically easy with Gnucap. Spice is a better 
candidate for that purpose. I think.

>
>> The module call directly spicelib or frontend functions.
>>
>> I 'd like to give an object oriented approach to the module,
>> so I need to clean the memory when a circuit is not used any
>> more (garbage collector).
>>
>> I use the  com_removecirc() function for that purpose but the
>> circuit is still
>> in ft_circuits list and a "run" causes a segmentation fault.
>>
>> Is there a function removing entirely a circuit from the
>> memory (database and circuits list) ?
>
> Spice: no (to all).  Spice is designed to load a circuit once, then 
> make only non-structural changes.  For a serious topology change, you 
> need to start over.
>
> Gnucap: yes (to all).  It is designed so you can make arbitrary 
> changes to the circuit.  It can even make some topology changes 
> dynamically as the simulation runs.
>
Yes Gnucap can clean its memory, but Gnucap handle only one circuit at a 
time. Resolution matrices are deleted then re-allocated so it's not 
possible the swap between circuit without a lot of work.

>> More over, it seems that the model name in a .cir file can't
>> contain ('/', '+', '-').
>> What are the rules for models name ?
>
> I think it is letters, numbers, and underscore.  Mostly not case 
> sensitive.  Actually, the rule is that it is not case sensitive, but 
> there are occasional surprises, like the FAT file system.  Model names 
> are supposed to start with a letter, but there are occasions where 
> this is not enforced.
>
>
In fact, I've asked this question because I've tried to use PSpice diode 
model in ngspice, and ngspice failed reading the lib, ngspice stuck on 
name model like "ABC12345/-67". It was with a win XP machine and ngspice 
rework 17 compiled with mingw.

Libraries are perhaps rewritten (by PSpice) before being read by the 
simulator ? Or the simulator is radicaly different ?

Cyril.