VHDL Issue Number:      0144
Classification:         Language Enhancement
Language Version:       VHDL-87
Summary:                Allow resolution functions to have an
                        extra parameter for the current value
                        of the signal.
Related Issues:         
Relevant LRM Sections:  2.4
Key Words and Phrases:  Resolution Function
Current Status:         Submitted
1076-1993 Disposition:  Bugs Fixed, Enhancements Outstanding (No ISAC Issues)
Disposition Rationale:  Non-ISAC issues outstanding.
Superseded By:          N/A
-----------------------
Date Submitted:             1989/06/21
Author of Submission:   Ken Scott
Author's Affiliation:   Vantage Analysis Systems, Inc.
Author's Post Address:  42840 Christy St., Suite 201
                        Fremont, CA   94538
Author's Phone Number:  (415) 659-0901
Author's Fax Number:    
Author's Net Address:   N/A
-----------------------
Date Analyzed:          TBD
Author of Analysis:     TBD
Revision Number:        $Revision: 1.9 $
Date Last Revised:      $Date: 1995/08/04 01:39:21 $


Description of Problem
----------------------
   It would be useful for resolution functions to be able to
   take into account the current value of the signal being
   resolved, as well as the new set of driving values.  

   The only thing close to this functionality currently is
   the signal kind REGISTER.  Registers have some drawbacks
   that make their usefulness less than desireable:
   - You cannot hierarchically decompose signals which are of
     kind REGISTER, because the semantics of the 'registerness'
     of the signal cannot be propagated to lower-level component
     instantiations.
   - Registers can only make use of the signal's current value
     in the case when ALL drivers have been turned OFF.  

   A more general-purpose utility would be to allow two forms
   of resolution functions.  The new type of resolution function
   would have the same first parameter and return value of the
   old resolution functions, but would also have a constant
   parameter of the same type as the return type.  The simulation
   kernel would pass to this value the current value of the signal
   being resolved.  The resolution function could then factor this
   information into its algorithm.

Proposed Resolution
-------------------
   Enhance the language as described above.  Modification to the 2nd
   paragraph of section 2.4 would be required.

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


VASG-ISAC Recommendation for IEEE Std 1076-1987
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VASG-ISAC Recommendation for Future Revisions
---------------------------------------------