Re: [sv-bc] FW: question: continuous assignments to variables

Bresticker, Shalom wrote:

> OK, let’s go one step further.
> 
> What if I replaced ‘assign’ with ‘always_comb’?

So:

   module test(output logic [3:0] out, input [3:0] in, input [0:1] idx);
     for (genvar I = 0; I < 4; I++)
        always_comb
           out[(idx+I)%4] = in[I];
   endmodule


In this case, the "idx" is not a static-prefix so the always_comb
is valid but is presumed to write to all bits of "out".  This
means that you should end up with errors since multiple always_comb
processes assign to the same output.

So it is still "wrong" but not quite in the manner that you
might expect.

Gord.


> Shalom
> 
>  
> 
> ------------------------------------------------------------------------
> 
> From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of Brad 
> Pierce
> Sent: Thursday, March 30, 2006 6:39 PM
> To: sv-bc@eda.org
> Subject: Re: [sv-bc] FW: question: continuous assignments to variables
> 
>  
> 
> Shalom,
> 
> The text should clarify that the left-hand side of a continuous 
> assignment must be structural, even if it is of a variable type.  The 
> following example would not be considered legal.
> 
> module test(output logic [3:0] out, input [3:0] in, input [0:1] idx);
> 
> for (genvar I = 0; I < 4; I++)
> 
>   assign out[(idx+I)%4] = in[I];
> 
> endmodule
> 
> ------------------------------------------------------------------------
> 
> From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of 
> Bresticker, Shalom
> Sent: Thursday, March 30, 2006 6:35 AM
> To: sv-bc@eda.org
> Subject: [sv-bc] FW: question: continuous assignments to variables
> 
>  
> 
> Hi,
> 
> I never got a response to this.
> 
> Shalom
> 
>  
> 
> ------------------------------------------------------------------------
> 
> From: Bresticker, Shalom
> Sent: Monday, February 27, 2006 1:57 PM
> To: sv-bc@eda.org
> Subject: question: continuous assignments to variables
> 
>  
> 
> Hi,
> 
>  
> 
> In 1364, if the LHS of a continuous assignment is a select, the select 
> needs to be a constant select.
> 
>  
> 
> 1800 says that the LHS of a continuous assignment can be a net or 
> variable of any data type. For a net, the BNF net_lvalue still seems to 
> restrict that to constant selects, but the text does not seem to mention 
> that restriction. It probably should, because one might interpret “any 
> data type” as relaxing that restriction.
> 
>  
> 
> But mainly, I want to ask about variables as LHS of a continuous 
> assignment. I don’t see that the BNF (variable_lvalue) restricts it to 
> have a constant select. Is that true? If so, why is there a difference 
> between variables and nets?
> 
>  
> 
> Thanks,
> 
> Shalom
> 
>  
> 
> Shalom Bresticker
> 
> Intel Jerusalem LAD DA
> 
> +972 2 589-6852
> 
> +972 54 721-1033
> 
> I don't represent Intel 
> 
>  
> 

-- 
--------------------------------------------------------------------
Gordon Vreugdenhil                                503-685-0808
Model Technology (Mentor Graphics)                gordonv@model.com