(r21) FunctionInterface < P1076

P1076 Web>Vhdl2019CollectedRequirements>FunctionInterface (revision 21) (raw view)~~EditAttach~~
---+ Allow access and protected type parameters on function interfaces

%TOC%

---++ Proposal Information
   * Current Owner: Main.JimLewis, ...
   * Contributors: Main.JimLewis, ...
   * Date Proposed: 2012-Aug-16
   * Date Last Updated: 2012-Aug-16
   * Priority:
   * Complexity:
   * Focus: Testbench
   * Related Issues: None
   * Competing Issues: None
---++ Language Change Specification Link

[[LCS2016_002][LCS-2016-002]]
---++ Requirement Summary

Allow access and protected types on function interfaces.

Allowed for ADA functions. See: http://en.wikibooks.org/wiki/Ada_Programming/Subprograms#Functions

---++ Use Model: Access Types

Currently it is not possible to create an !EmptyLine (named consistent with !EndFile and original name before removed) Usage:

<verbatim>next when EmptyLine(buf) ;


function EmptyLine (
    variable L     : inout Line 
) return boolean is
    variable Valid : boolean ;
    variable Char  : character ;
begin
    skip_whitespace(L) ; 
    return L = null or L.all'length = 0 ;
end function EmptyLine ;</verbatim>

Then we would also be able to create a to_string for type line that also deallocates a line:

<verbatim>function to_string(  variable L : inout line ) return string is 
  variable result : string(L'range) ; 
begin
  result := L.all ;
  deallocate(L) ; 
  return result ; 
end function to_string ; </verbatim>

Then to create a to_string for composite types, such as integer_vector, where "write" is already defined can be done as follows:

<verbatim>function to_string(  IV : in integer_vector ) return string is 
  variable L : line ; 
begin
  write(L, IV) ; 
  return to_string(L) ; 
end function to_string ; </verbatim>

Or alternately we can leverage generics:

<verbatim>function generic_to_string
generic( 
    type AType ; 
    procedure write(L : inout line ; A : AType ;  JUSTIFIED : SIDE := right; FIELD : WIDTH := 0) is <> 
) ; 
parameter(  
    A : in AType 
) return string is 
    variable L : line ; 
begin
    write(L, A) ; 
    return to_string(L) ; 
end function generic_to_string ; </verbatim>

With generics, a to_string function for integer_vector becomes:

<verbatim>function to_string is new generic_to_string 
    generic map (AType => integer_vector) ; </verbatim>

Another usage is within coverage modeling for the OSVVM package "CoveragePkg", however, the background information for the justification dives deeply into data structures for coverage modeling.

---+++ Extend Concatenation

Allow concatenation of types that are access types or composites that contain access types.

---++ Use Model: Protected Type

Motivation: Local customizations and extensions to a protected type interface

---+++ Layering on top of !CoveragePkg and !RandomPkg
<verbatim>function RandCovPoint(
  variable RV       : inout RandomPType ;
  constant Bin      : in    RangeArrayType 
) return integer_vector is
  variable result : integer_vector(Bin'range) ;
begin
    for i in Bin'range loop
        result(i) := RV.RandInt(Bin(i).min, Bin(i).max) ;
    end loop ;
    return result ; 
end procedure RandCovPoint ;</verbatim>

---+++ Modeling Semaphores

See [[SemaphoreDataStructure]]

Currently VHDL functions do not allow either access types or Protected Type inputs. ADA removed the requirement for not allowing access type inputs in ADA-95. This would allow overloads like the non-protected type procedure TryGet [SemaphorePType, Boolean, Integer] to be re-expressed as a function TryGet [SemaphorePType, Integer return boolean] which is a more natural way to use it. The code is as follows

<verbatim>
  function TryGet (Semaphore : SemaphorePType ; Count : Integer := 1 ) return boolean is
  begin
    return Semaphore.TryGet(Count) ; 
  end function TryGet ;</verbatim>

---++ Proposal

---++ Comments

This relaxation should be limited to impure functions, because the function may have side effects. -- Main.PeterFlake - 2014-12-18
---+++ General

---+++ Arguments Against

---++ Supporters

_Add your signature here to indicate your support for the proposal_

-- Main.JimLewis

-- Main.KevinJennings - 2013-04-12

-- [[Main.BrentHahoe][Brent Hayhoe]] - 2014-12-23

-- Main.MortenZilmer - 2015-01-21

-- Main.PatrickLehmann - 2016-02-19

-- Main.TorstenMeissner - 2016-05-18
Topic revision: r1 - 2020-02-17 - 15:34:31 - TWikiGuest
P1076