Re: [vhdl-200x] interface proposals

On 23/11/15 20:26, Brent Hayhoe wrote:
> Hi Tristan,
>
> On 22/11/2015 11:40, Tristan Gingold wrote:
>> On 22/11/15 11:56, Brent Hayhoe wrote:
>>> Some thoughts:
>>>
>>> -- So this is the Ada 'discriminated record' type that I presume we are
>>> -- discussing. The way it looks to me is just a 'constant generic'
>>> applied to -- the record type:
>>>
>>> type Discriminated_Record (Size : Natural) is
>>>     record
>>>        A : String (1 .. Size);
>>>     end record;
>>>
>>> -- So if I VHDL'asize this we could have a generic block preceding the
>>> record
>>> -- block in the type declaration.
>>>
>>> -- We then need to 'generic map' the 'Size' value through when we
>>> declare a
>>> -- constant and signals:
>>>
>>> type MyRecType is
>>>     generic(
>>>        Size : Natural
>>>     );
>>>     record
>>>        A : String (1 to Size);
>>>     end record MyRecType;
>>
>> Isn't this a little bit overkill given that it is already possible
>> to have unbounded arrays as record elements ?
>
> Not if you want to do something like:
>
> entity MyEntity is
>     generic(
>        Size : Natural := 10
>     );
>     port(
>        IP : in  MyRecType generic map(Size);
>        OP : out MyRecType generic map(Size)
>     );
> end entity MyEntity;
>
> You could decompose the records at the port, but with bigger record
> structures this will become very cumbersome.

My point is that this overlaps record_constraint.  What would be the 
syntax if you have both ?  Would that be readable ?

Beside the syntax, the semantic is not clear to me.  When you 
'instantiate' a type, is it a new type or a subtype ?

The complexity becomes very high.

What is wrong with:

type MyRecType is record
   A : String;
end record;

entity MyEntity is
   port (IP : in MyRecType;
         OP : out MyRecType);
end MyEntity;

[ In Ada, the discriminants is either a discrete type or an access type. 
  I suppose vhdl is not interested in access type here.  But setting the 
discriminant doesn't create a new type.  Furthermore it is possible to 
change the discriminant(s) under some restrictions. ]