RE: [sv-cc] Value change callbacks with variable indexes -- and (not) for automatic variables

Jim,

With respect to what $monitor is sensitive to, see Mantis 1040.

Regards,
Shalom 

> At Charles's suggestion, I checked with a member of the 
> now-defunct PLI Task Force, David Roberts.  He recalled a 
> long-ago but vigorous discussion of what a cbValueChange 
> callback should be sensitive to.  
> The task force's decision was to be consistent with the 
> sensitivity of event control expressions and $monitor() 
> arguments.  One can poke around the LRM for statements about 
> what that means, but in short:
> 
> "... when you put a callback on a[i] you should get a 
> callback when ever the value pointed at by a[i] changes.  
> This can happen because the value in the object index by "i" changes
>    reg a[3:0];
> 
>    i = 0;
>      put cb on a[i].
>    now update the value of a[0].  a[0] = 1;
>        a[i] just went from an X to 1.
> 
> the callback should fire when "i" changes if and only if the 
> value that a[i] now points is different then what it was from 
> the last time the callback fired.
> 
> ...
> 
> And yes we have to handle the case when the index goes out of range.  
> For that case the value is "X"; this behavior is defined by 
> the Verilog HDL language."
> 
> So at this point I'm thinking of simplifying our description 
> of what is and is not supported by referring to what event 
> control statements and
> $monitor() arguments can handle and are sensitive to.
> 
> Incidentally, one side effect of this is that we can probably 
> exclude automatic variables and their subelements as value 
> change arguments, since the $monitor() system task does not 
> allow them (Draft 4, 13.3.2).
> 
> I don't know yet if they can be used as event control 
> expressions, though.
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