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

DOULOS - Developing Design Know-how
VHDL * Verilog * SystemC * e * Perl * Tcl/Tk * Project Services

Doulos Ltd. Church Hatch, 22 Market Place, Ringwood, Hampshire, BH24 1AW, UK
Tel: +44 (0)1425 471223                   Email: jonathan.bromley@doulos.com
Fax: +44 (0)1425 471573                           Web: http://www.doulos.com

This e-mail and any  attachments are  confidential and Doulos Ltd. reserves 
all rights of privilege in  respect thereof. It is intended for the use of 
the addressee only. If you are not the intended recipient please delete it 
from  your  system, any  use, disclosure, or copying  of this  document is 
unauthorised. The contents of this message may contain personal views which 
are not the views of Doulos Ltd., unless specifically stated.

-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.