Re: hierarchical parameter passing in DC sweep

Martin -

> FYI - I have uploaded the dynamic parameter proposal to the DB in issue 814.

I see the following statement in the proposal:
    The dynamic parameters are set once before the start of an analysis, and
    are then constant during the simulation of the analysis.

This seems to prohibit a dc sweep of a dynamicparam, which was
a big part of the motivation.


I also think it's a nuisance to have to declare dynamicparams
for compact models.  It's the sort of thing that a model writer
should not have to think about: what might the analog circuit
designer / compact model user want to vary?  L and W for sure,
VTH likely, and possibly anything else -- particularly if the
user is a characterization engineer trying to fit to data.
If the module is in a read-only location, or provided pre-
compiled or encrypted, what is the user to do?


It also seems to me that all the Spice-like simulators that
support Verilog-A allow standard "parameters" to be varied.
(I haven't been able to reproduce Marq's problem with 
simulators I have access to.)  Is "dynamicparam" a solution
looking for a problem?

If the simulator supports dc sweeps, then the Verilog-A
compiler should be able to set up dependency trees and figure
out which computations need to be done once per sim, once
per dc point, or every iteration.  If it only supports
transient, then it is free to optimize parameters as constants
just as Verilog-D simulators do now.  (Your proposal does add
one new feature, multiple transient analyses in one simulation
with different values of a dynamicparam, without re-netlisting/
re-elaborating.  But I haven't heard anyone on the Verilog-D side
requesting this feature.  Probably, if you want multiple
transient analyses, it's faster to generate two netlists and run
the analyses on two compute farm machines.)


Another secondary concern is that SystemVerilog has a sentence
to the effect that defparam may be deprecated in the next version,
but your proposal requires defparam to allow dynamicparams to
affect other modules through OOMRs.

-Geoffrey