Re: Compilation question

Geoffrey.Coram wrote:

>Shalom -
>There is perhaps a difference in understanding of what "compilation"
>means.  In the Verilog-A compact modeling world, we have these
>very complicated modules that get "compiled" from Verilog-A to
>C and then to object code that is dynamically linked into the
>simulator.  This is somewhat different from the "compilation"
>that I think digital Verilog simulators do when they set up
>a particular netlist to run (and run quickly).
>  
>
Pretty much the same for digital these days.

>LRM 2.2 does, indeed, have that paragraph -- taken directly
>from 1364-1995 (section 3.10).  All the analog simulators
>I've used take that with a nudge and a wink and allow the
>parameter value to be changed.  Of course, since the 1364
>LRM doesn't know what a "dc sweep" is, one could argue that
>a "dc sweep" is really a set of runs, in each of which the
>parameter value is constant.  I believe there are open issues
>for Verilog-AMS about cleaning up the mixed-signal initialization
>and fully explaining what a "dc sweep" means.
>  
>
There's nothing to stop vendors giving users a compile option to make 
parameters run-time constants or runtime variables, how you actually 
modify them during a run and what the scope of the change is is up for 
debate. E.g. if you have a default temperature parameter that is passed 
down the hierarchy then if you change it at the top wouldn't you want it 
to change all the way down? - in which case you want it to behave more 
like a signal (you don't want to use a signal if your tools are going to 
think it's a real [physical] wire). Most of this kind of stuff can be 
fixed by the use of syntax like 'const' and using references rather than 
copying values around - don't know if SV supports parameter references, 
maybe it needs to be added.

Kev.

>-Geoffrey
>
>
>"Bresticker, Shalom" wrote:
>  
>
>>On the contrary, the 2.2 LRM says,
>>
>>"Parameters represent constants, hence it is illegal to modify their
>>value at runtime. However, parameters can be modified at compilation
>>time to have values which are different from those specified in the
>>declaration assignment. This allows customization of module instances. A
>>parameter can be modified with the defparam statement or in the
>>module_instance statement."
>>
>>A -defparam on the command line is just a substitute for a defparam
>>statement in the code. It is still evaluated at compilation time.
>>
>>You should have some basic understanding of what compilers do.
>>Among others things, compilers translate the source code into a data
>>structure. Changing the data structure requires a recompilation. It may
>>be an incremental recompilation, but a recompilation nevertheless.
>>
>>There might be special cases of parameters which you could change
>>without requiring a recompilation, such as a transistor value, but that
>>is not changing the data structure.
>>
>>Shalom
>>    
>>
>
>  
>