RE: [sv-bc] Pre-Proposal to handle X-problems in RTL coding

Yes, but I also want pre-defaults for case statements which really are
not parallel.

Cliff was saying that if you have unique0, then you don't need
pre-defaults. 
I was saying that pre-defaults are useful even where I don't want
unique0.

Shalom  

> -----Original Message-----
> From: Jonathan Bromley [mailto:jonathan.bromley@doulos.com] 
> Sent: Wednesday, November 07, 2007 12:54 PM
> To: Bresticker, Shalom; Clifford E. Cummings; sv-bc@server.eda.org
> Subject: RE: [sv-bc] Pre-Proposal to handle X-problems in RTL coding
> 
> Shalom wrote:
> 
> > [Cliff has] proposed unique0 (parallel_case) as obviating 
> the need for 
> > pre-defaults. I don't see the necessary connection.
> 
> I agree, but I suspect we're juggling words here...
> I see "unique0" (I like the name) as a way to avoid an 
> unnecessary *case-default* in situations where you have 
> *chosen* to use an explicit pre-default:
> 
>   always_comb begin
>     code2 = 1'b0; code1 = 1'b0;
>     unique case (onehot_code) inside
>       4'b??1?: code1 = 1'b1;
>       4'b?1??: code2 = 1'b1;
>       default: ;
>     endcase
>   end
> 
> In this example, the default branch is *only* needed to keep 
> "unique" happy, since "unique" also requires full-case and 
> therefore would throw an error on the valid but irrelevant 
> codes 1000, 0001.  The "pre-default" 
> is there for other reasons, and is required whether or not 
> the case statement is full or parallel.
> 
> With "unique0" I could spare myself the misleading and 
> unnecessary default clause on the case statement, but still 
> get the checking for non-overlap of the case branches.
> --
> Jonathan Bromley, Consultant
> 
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