VHDL Issue Number:      0073
Classification:         Language Definition Problem
Language Version:       VHDL-87
Summary:                Use of block configurations with mixed generates and
                        blocks unclear.
Related Issues:         
Relevant LRM Sections:  1.3.1
Key Words and Phrases:  Generate statements, block configurations
Current Status:         Submitted
1076-1993 Disposition:  Closed (All Issues Completely Addressed)
Disposition Rationale:  Now have declarative region for generates.
Superseded By:          N/A
-----------------------
Date Submitted:         1989/02/10
Author of Submission:   Doug Dunlop
Author's Affiliation:   Intermetrics, Inc.
Author's Post Address:  4733 Bethesda Ave #415
                        Bethesda, MD  20814
Author's Phone Number:  (301) 657-3775
Author's Fax Number:    
Author's Net Address:   dunlop@inmet.inmet.com
-----------------------
Date Analyzed:          TBD
Author of Analysis:     TBD
Revision Number:        $Revision: 1.8 $
Date Last Revised:      $Date: 1995/08/03 17:15:49 $


Description of Problem
----------------------
The LRM allows block configurations to apply to generate
statements.  It is unclear what the rules are for using block configurations
when the corresponding architecture body has mixed and nested block statements
and generate statements.

The confusion is due to the use of the phrases "the block", "the given block",
and "within a given block" in the paragraph beginning "If a block configuration
appears immediately wihin another ..." and the paragraphs beginning "For any
name ..." of LRM 1.3.1.  To make sense and to be consistent, "block" here
should mean "block statement or generate statement".  Similarly "within" in
these paragraphs should be taken to mean "immediately within".


Proposed Resolution
-------------------
The above interpretation of these paragraphs is assumed.  Thus
these paragraphs are read as (with changes in upper case):

  If a block configuration appears immediately within another block
  configuration, then the block specification of the contained block
  configuration must be a block statement or generate statment label,
  and the label must denote a block statement or generate statement
  that is contained immediately within the BLOCK STATEMENT OR GENERATE
  STATEMENT denoted by the block specification of the containing block
  configuration.

  For any name that is the label of a block statement appearing
  IMMEDIATELY WITHIN a given BLOCK STATEMENT OR GENERATE STATEMENT,
  a corresponding block configuration may appear as a configuration
  item IMMEDIATELY WITHIN a block configuration corresponding to the
  given BLOCK STATEMENT OR GENERATE STATEMENT.  For any collection of
  names that are labels of instances of the same component appearing
  IMMEDIATELY WITHIN a given BLOCK STATEMENT OR GENERATE STATEMENT,
  a corresponding component configuration may appear as a configuration
  item IMMEDIATELY WITHIN a block configuration corresponding to the
  given BLOCK STATEMENT OR GENERATE STATEMENT.

  For any name that is the label of a generate statement IMMEDIATELY
  WITHIN a given BLOCK STATEMENT OR GENERATE STATEMENT, one or more
  corresponding block configurations may appear as configuration items
  IMMEDIATELY WITHIN a block configuration corresponding to the given
  BLOCK STATEMENT OR GENERATE STATEMENT. ...

To illustrate this, consider the following entity and architecture definition:

entity E is
  generic(N : Positive);
  port(P : out Bit);
end E;
--------------------------------------------------------------------------------
use Work.E;
architecture A of E is
begin
   G1 : if N > 1 generate
           L:block
                signal S : Bit;
                component C generic(N : Positive); port(P : out Bit);
                end component;
             begin
                I:C generic map(N => N - 1) port map(P => S);
                P <= not S; 
             end block;
        end generate;
   G2 : if N = 1 generate
           P <= '0';
        end generate;
end A;

To write a component configuration that applies to the statement labelled "I",
this component configuration must be contained in a block configuration that
applies to block "L" that in turn must be contained in a block configuration
that applies to generate statement "G1" as in

use Work.E;
configuration C1 of E is
   for A
      for G1
         for L
            for I : C use entity E(A); end for;
         end for;
      end for;
   end for;
end C1;


VASG-ISAC Analysis & Rationale
------------------------------
TBD


VASG-ISAC Recommendation for IEEE Std 1076-1987
-----------------------------------------------
TBD


VASG-ISAC Recommendation for Future Revisions
---------------------------------------------
TBD