From: Stuart Sutherland (stuart@sutherland.com)
Date: Wed Jul 21 1999 - 12:09:45 PDT
Behavioral Task Force;
It seems my query about specparam bit selects has opened a can of worms. I
have two requests for the BTF:
1. Open a BE errata on the legality of specparam bit selects, so it is
documented.
2. *PLEASE* resolve the question by Monday, July 26th!
Even as soon as Monday may be too late for the PLI task force to implement
the changes that have been made on specparams in the PLI. But if you can
get an answer to us on Monday, we will try to have something for the July
29th final vote meeting.
Thanks,
Stu
At 11:15 AM 7/21/99, Michael McNamara wrote:
>
>Ted Elkind writes:
> > Hi Stu,
> >
> > In case no one replied yet, specparams cannot be accessed with bit or
> > part selects. They can only provide time or delay values or mtm
> > triples. However, they can always appear anywhere in a time or delay
> > expression. They cannot appear outside that context. Hence, this is
> > legal:
> >
> > specparam x = 5:6;7;
> > ...
> > #x Q = DAT;
> >
> > But this is not:
> >
> > specparam x = 5:6;7;
> > reg y;
> > reg [7:0] z;
> > ...
> > y = z[x];
> >
> > And neither is this:
> >
> > specparam [7:0] x = 5:6:7;
> >
> > Ted
>
>It is interesting that you state that later two usages are illegal.
>
>VCS agrees with you about the illegality, but both Verilog-XL and NC
>verilog accept everything you say is illegal.
>
>Consider:
>
>module xx;
> specify
> specparam[0:3] A = 3:4:5 ;
> endspecify
>
> wire [3:0] W1 = {A[3],A[2],A[1],A[0]} ;
>
> initial begin
> $display( "A= %b", A ) ;
> #10
> $display( "W1= %b", W1 ) ;
> end
>
>
>endmodule
>
>Worse, customers using our coverage tools have reported that vendor
>libraries are using specparams in many ways that the 1364
>specification, and you say are illegal.
>
>Since NC and Verilog-XL accept these usages, venders are doing it, and
>hence the rest of the industry gets pushed to support it.
>
>*sigh*
>
>-mac
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Stuart Sutherland Sutherland HDL Inc.
stuart@sutherland.com 22805 SW 92nd Place
phone: 503-692-0898 Tualatin, OR 97062
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