How to pass an array type as generic type parameter to a VHDL package?

Question

I'm working on a generic package (list) in VHDL-2008. This package has a type generic for the element type. If I declare an array type of this element type within the package, it's a new type. So for e.g. integer, my new integer_array would be incompatible with integer_vector from library ieee.

So I need also to pass in the array type (e.g. integer_vector). When an array instance of that array type is used with a 'range attribute, it gives me a warning in QuestaSim:

Prefix of attribute "range" must be appropriate for an array object or must denote an array subtype.

How do a denote that a generic type parameter is an array?

Generic Package:

package SortListGenericPkg is
  generic (
    type ElementType;  -- e.g. integer
    type ArrayofElementType;  -- e.g. integer_vector
    function LessThan(L : ElementType; R : ElementType) return boolean;     -- e.g. "<"
    function LessEqual(L : ElementType; R : ElementType) return boolean     -- e.g. "<="
  );

  function inside (constant E : ElementType; constant A : in ArrayofElementType) return boolean;
end package;

package body SortListGenericPkg is
  function inside (constant E : ElementType; constant A : in ArrayofElementType) return boolean is
  begin
    for i in A'range loop  -- this line causes the error
      if E = A(i) then
        return TRUE ;
      end if ;
    end loop ;
    return FALSE ;
  end function inside ;
end package body;

Instantiation:

package SortListPkg is
  package SortListPkg_int is new work.SortListGenericPkg
    generic map (
      ElementType        => integer,
      ArrayofElementType => integer_vector,
      LessThan           => "<",
      LessEqual          => "<="
    );
  alias Integer_SortList is SortListPkg_int.SortListPType;
end package SortListPkg ;

IEEE Std 1076-2008 16.2.3 Predefined attributes of arrays, A'RANGE, Prefix: Any prefix A that is appropriate for an array object, or an alias thereof, or that denotes an array subtype whose index ranges are defined by a constraint. ArrayofElementType class and subtype are not known until after elaboration. 6.5.3 Interface type declarations The set of values and applicable operations for an interface type may be determined by an associated subtype in the environment., ...an undefined base type and a subtype of the base type. The class (see 5.1) of the base type is not defined. — user1155120
– user1155120, Commented Nov 15, 2016 at 3:02

Morten Zilmer · Accepted Answer · 2016-11-14 19:54:59Z

1

ModelSim makes a similar error/warning, so it's maybe a VHDL standard issues.

A workaround is to declare ArrayofElementType as part of the package, like:

package SortListGenericPkg is
  generic (
    type ElementType  -- e.g. integer
  );
  type ArrayofElementType is array (integer range <>) of ElementType;
  function inside(constant E : ElementType; constant A : in ArrayofElementType) return boolean;
end package;

and then convert the argument when inside is called, like:

... inside(int, ArrayofElementType(int_vec));

or simple use ArrayofElementType as type when declaring the argument if possible/feasible.

answered Nov 14, 2016 at 19:54

Morten Zilmer

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4 Comments

Paebbels Over a year ago

Can I convert both array? Aren't they considered different incompatible types? How can I do the reverse conversion?

Paebbels Over a year ago

QuestaSim shows this error:

** Error: (vcom-1583) Illegal type converson from 'work.SortListGenericPkg.ArrayofElementType' to 'work.SortListGenericPkg.ArrayofElementType_Internal' (non-numeric to array).

The first parameter isn't known to be an array. Edit: oh it's on the caller side ...

Paebbels Over a year ago

As far as I can tell it works. But at least we noticed - while discussing the issue in the new VHDL Gitter channel - that VHDL needs a concept to specify the kind of a type parameter in package generic lists.

Morten Zilmer Over a year ago

Conversion in both directions are possible, since both types are available. I read briefly through the VHDL Gitter channel. Maybe implicit type conversion to destination type could be an alternative.

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