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Re: [Gnucap-devel] New Developer

From: al davis
Subject: Re: [Gnucap-devel] New Developer
Date: Tue, 20 Feb 2007 01:34:33 -0500
User-agent: KMail/1.9.5

On Monday 19 February 2007 19:49, David Cummings wrote:
> Hi all,
>     I'm interested in helping out with the project, more
> specifically, i'm interested in an alternative to SPICE. The
> website seems to be full of old(er) information (just found
> the one on, maybe they should be connected? I'd be
> willing to help out with some web-devel, though it really
> grinds the nerves (bad memories of cross-browser
> compatibility).

That is obviously a place where help is desperately needed.  The 
latest is at, but even that needs lots of work.  The 
one at is supposed to be a mirror of it.  The one 
at is supposed to be a checkout of the CVS archive of 
the one at 

> What's the status on IBIS? How hard would it 
> be to complete? 

IBIS-3 is about 90% complete, and on hold, but it is designed 
around an older version of gnucap, assuming a Spice-style 
netlist.  It needs to be changed to use a Verilog style 
netlist, and to work directly as a plug-in.

The important part that is still missing is part of the waveform 
generator.  I know how to do it, but have had other priorities.  
It is conceptually difficult and requires expert knowledge.

> Also, has anyone done any work on harmonic 
> balance simulation? That seems interesting, though probably
> fairly difficult.


I have given some serious thought about periodic steady state by 
a shooting method.  This should be fairly easy.  Most of the 
infrastructure is in place.  I have done some proof of concept 
experiments but no real code.  The proof of concept experiments 
were successful.  I was able to measure distortion of a high 
quality oscillator by manually manipulating the shooting 
parameters.  The  procedure is fairly easy.  It just needs to 
be coded.  The most likely user interface is an option on the 
Fourier command, which almost does all you need now.

>     About me: I'm a senior at JHU studying computer
> engineering. I've worked on some midsize C++ projects (>20k
> lines) and am decent on teams. As a senior, my time is kinda
> limited, but I could try and help with the web while I spin
> up on the code. I'm taking a class on analog integrated
> circuits this semester, so some of this stuff is very current
> for me. I've taken classes on circuit analysis, parallel
> programming, etc., so I at least know the basic idea, which
> is to say I know very little in the grand scheme of things.

Johns Hopkins???

Try using gnucap for your homework.  Your teacher probably told 
you to use something else.  Try both and compare.  Gnucap will 
give you a lot more information about your circuit than you can 
get out of any Spice, but you need to know how to ask for it.

The main focus of current work is to move as much as possible 
into plug-ins.  That makes it much easier to extend and 
experiment.  You can experiment in a plug-in without the 
baggage of dealing with the whole thing.  You can distribute 
experimental code without contaminating the core.  

The other main focus, which needs plugins to work, is real 
Verilog-AMS support.

>    Anyway, sorry about the slow introduction, just wondering
> how I can help, and if there's a repository somewhere with
> the current development code.

There is no CVS yet.  I have been trying to get the plugins and 
at least part of Verilog-AMS working, which has been taking all 
of my time.

The best code to work on is the latest development snapshot.  
There will be a new one within a few days.  I recommend that 
you wait for the announcement, then get the new one.  This one 
will have 4 tarballs to get everything.  That is one for the 
simulator, and 3 more for models.  The new one can use Spice C 
models as plugins, with a wrapper.

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