RE: gEDA-user: Symbol Usage

[John Davies <john.davies@metagence.com>]

Hi All.

Thank you for the responses.

I have looked at gnet-spice.scm, as suggested, to try to find the line of
code that inserts the uref, followed by the symbol output nodes, followed by
the symbol input nodes into the netlist output.  My intention was to hack
this so that an attribute called, say, type was inserted between the output
nodes and the input nodes.  I think that this should give me what I need.
Unfortunately, I cannot find the relevant line of code.  Not very surprising
really since I am an Analogue specialist.

Could someone out there point me in the right direction?

Bas mentioned that + and - were impossible, but I was just using these
characters as an example.

Best regards
John Davies
Metagence Technologies
Home Park Estate, Kings Langley, Herts WD4 8LZ
Tel: +44 (0)1923 260511 Fax: +44 (0)1923 268969




-----Original Message-----
From: Bas Gieltjes [mailto:S.Gieltjes@ITS.TUDelft.nl]
Sent: 05 February 2002 22:28
To: geda-user@seul.org
Subject: Re: gEDA-user: Symbol Usage


On Tue, 5 Feb 2002, John Davies wrote:

> Hi All.

Hello John and others,
 
> I have been using gschem and gnetlist and would prefer not to edit any
> netlists that are created from gschem.  My thinking is that this could
lead
> to errors in the simulation, etc.  Therefore I would like to be able to
> generate SPICE functions directly from the symbol.  The closest symbol
> available for my needs is the VCVS in the gschem SPICE library.  This
> produces a line in the netlist:-
> 
> Exx out+ out- in+ in- value
> 
> I can include anything I like in "value" since this is an attribute.  But
> what I would really like to do is change the netlist to:-
> 
> Exx out+ out- transformer in+ in- value
> 
> Transformer is just an example.  It could be "laplace" for filters, etc.
> There are many examples in SPICE where this type of netlist line is
needed.
> 
> Any suggestions as to what I can do to the symbol to change it?

Changing the symbol won't help, changing the code in gnet-spice.scm is
part of the solution. I just copied a part of the pspice (7,x) manual with
controlling sources and found that there are several forms of the above
example. Berkeley spice has a separate non-linear source (B), the main
reason not to implement these pspice controlling sources.

Attaching attributes to a symbol and changing the scheme code that
generates the netlists is a solution. What about the proposed scheme
below?

Attaching attributes to symbols like this:
value=<gain>       (currently implemented) or
value=<expression>  

poly=<value>, value=<polynomial coefficients> or
poly=(<value>) = <polynomial coefficients>

table=<expression>, value=<input value, output value>  or 
table=<expression> = <input value, output value>

laplace=<expression>, value=<transform> or 
laplace=<expression> = <transform>

freq=<expression>, value=<frequency, magnitude, phase> <delay> or 
freq=<expression> = <frequency, magnitude, phase> <delay>

chebychev=<expression>, value=<transform> or 
chebychev=<expression> = <lp,hp,bp,br>,<cutoff frequency>, <attenuation>

The second form of poly, table, laplace, freq and chebychev is probably
the easiest method to attach attributes to a symbol. Now the node
reference used in the expressions, using '+' or '-' is impossible, these
math symbols are used to  generate the expressions. Referring to the
controlling node with 'plus' and 'minus' is better.

Another related topic:

I am unaware of all the different model parameters that the different
spice simulators accepts. For other components (e.g. BJT, MOSFET,
GaAsFET,... ) the scheme where you attach a list of attributes that can be
used to generate a spice netlist could be useful. E.g. attach an attribute
that contains a list of attributes that a model accepts. When the model
contains a valid attribute from the list it appears in the netlist.

For a MOSFET attach these attributes:
spiceattributelist=l w ad as pd ps nrd nrs nrg nrb
l=<value>
w=<value> 
pd=<value>
nrg=<value>

A example line of the generated netlist from the component with the above 
attributes:
M drain gate source bulk model l=<value> w=<value> pd=<value> nrg=<value> 

The attributes not present (ad, as, ps, nrd, nrs, nrb) are not netlisted.

Is this last example a useful addition to the gnetlist spice capabilities?
Are there better methods to implement the above feature?


> By the way, I am looking forward to trying gspice.
> 
> Best regards
> John Davies
> Metagence Technologies
> Home Park Estate, Kings Langley, Herts WD4 8LZ
> Tel: +44 (0)1923 260511 Fax: +44 (0)1923 268969


 Bas
--