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VHDL Issue Number:        2083

Language_Version          VHDL-2002
Classification            Language Definition Problem
Summary                   Generate index specification should be of same subtype as generate parameter
Relevant_LRM_Sections     1.3.1 Block configuration
                          9.7 Generate statements
                          12.4.2 Generate statements
Related_Issues            
Key_Words_and_Phrases     generate parameter, block configuration, 
                          index specification
Authors_Name              Peter Ashenden
Authors_Phone_Number      +61 414 709 106
Authors_Fax_Number        
Authors_Email_Address     peter@ashenden.com.au
Authors_Affiliation       Ashenden Designs
Authors_Address1          
Authors_Address2          
Authors_Address3          

Current Status:           VASG-Approved

Superseded By:

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Date Submitted:           31 January 2006
Date Analyzed:            15 March 2006
Author of Analysis:       Chuck Swart
Revision Number:          4
Date Last Revised:        04 May 2006

Description of Problem
----------------------

I've just been looking at generate statements, and am having trouble
finding rules that I thought should exist.
    
    A for-generate statement specifies values for the generate
    parameter with a discrete range. The implicit type of the generate
    parameter is the base type of the discrete range.
    
    In a block configuration for the generate statement, you can write
    a block specification that determines which occurrences of the
    generate get configured. The block specification can be either a
    discrete range or an expression.
    
    I would expect the type of the discrete range or expression to be
    that of the generate parameter, and that values in the discrete
    range or the value of the expression be in the discrete range of
    the generate statement. However, I can't find rules that state
    this.

Proposed Resolution
-------------------

If no such rule exists anywhere, add a rule to 1.3.1 specifying that
the value or values of the index specification be of the type of the
corresponding generate parameter and lie within the discrete range
specified for the generate parameter.

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

The submitter is correct. The rules he describes do not exist in the
LRM.

VASG-ISAC Recommendation for IEEE Std 1076-2002
-----------------------------------------------

Interpret the LRM as if the Recommendation for Future Revisions had
been adopted.

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

In clause 1.3.1 there is a paragraph which reads:

    "If the block specification of a block configuration contains a
    generate statement label, and if this label contains an index
    specification, the it is an error if the generate statement
    denoted by the label does not have a generation scheme including
    the reserved word for."

Add to the end of this paragraph:

    "In addition, the value (or values) of the index specification
    must be of the type of the corresponding generate parameter and
    this value (or these values) must belong to the discrete range
    specified for the generate parameter."


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