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Re: [Gnucap-devel] Hierarchical name ordering

From: a r
Subject: Re: [Gnucap-devel] Hierarchical name ordering
Date: Sat, 19 Jan 2008 22:20:59 +0000

On Jan 19, 2008 8:47 PM, al davis <address@hidden> wrote:
> On Saturday 19 January 2008, a r wrote:
> > What I would like to be able to do is:
> >
> > X1 (1 2) foo bob=2k
> ..  an instance "X1" of "foo" (whatever that is) with a
> parameter "bob" set to "2k"
> > .alter different subcircuit
> ?

That's hspice's (and spectre's) way of restarting the simulation with
some changes to the circuit. "different subcircuit" is a new
simulation title. Any cards that follow ".alter" override cards from
the previously defined circuit.

That was just an example. I thought you are familiar with this syntax, sorry.

A number of:
> Violates encapsulation, and really screws things up.

I disagree. At testbench level encapsulation is no longer an issue.
Sure, people want encapsulation but that's only true at design stage.
Global parameters, global connections are almost always forbidden
nowadays. However, people do want a full transparency of the design at
evaluation stage. That's why I asked for probing internal net voltages
in the first place.

> Suppose I have:
> X1 (1 2) bar bob=x1bob
> X2 (3 4) bar bob=x2bob
> X1 and X2 are structurally identical, and must remain so.  They
> share storage.  Some calculations are shared.  In future, they
> may share a cache.

Why? You mean you want to continue the simulation after the circuit
topology changes? That was not what I meant. It's rather "once the
simulation ends, modify the circuit (in any way you like) and rerun
previous analyses (or start some new ones)". I didn't propose doing
such (or any) changes to the circuit on the fly.

Again, this was just an extension of our discussion on probing
internal voltages. If you don't like this scheme there is no problem
at all - starting many separate simulations will do fine. In fact the
only benefit of ".alter" or similar commands is that waveform viewers
are usually smart enough to display results of such simulations as a
set of waveforms (a sweep).


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