RE: [sv-bc] Defparam on member of parameter struct

At 02:17 AM 11/8/2005, Bresticker, Shalom wrote:
>However, the statement
>
>"The defparam statement is particularly useful for grouping
>all of the
>parameter value override assignments together in one module."
>
>is still true.

This is Shalom's opinion and I disagree. I consider this to be one of the 
problems with defparams.

This is one reason why Verilog compilers do not know the true values of any 
of the design parameters until the last file is read because the last file 
may change every single parameter in an entire design. This is why some 
companies have the policy "thou shalt not use defparams" because it makes 
it real hard to create Verilog-related internal tools.

Another problem with all defparams in a separate file is that somebody may 
have put a defparam next to an instance and now the defparams are 
file-compile-order dependent, not to mention confusing to the engineer who 
does not understand why the defparam placed next to the file "did not work."

IMO - parameters are constants that are local to a module. Handling local 
constants from a global file is an extremely dangerous practice. I would 
like to see a serious design that uses this technique to see if I could 
recommend a superior methodology. One technique that comes to mind is to 
include top-level parameter definitions and have them passed by named 
parameter passing to the lower-level modules. A second technique is to have 
a `defines file that is compiled first and used to assign parameter values 
that are then passed by named parameter passing.

>Similar to the way we have lists of `defines.

Also IMO - engineers use too many `define macros as opposed to parameters. 
I recommend that engineers use parameters first, and then convince 
themselves that they really need a globally visible and compile-order 
dependent macro definition. When using the `defines file, I recommend 
compiling this file first and treat the `defines like true global definitions.

>Shalom

Shalom and have had many spirited discussions on the topics of defparams, 
but I still think he's an okay guy!   :-)  :-)

Regards - Cliff


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Cliff Cummings - Sunburst Design, Inc.
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