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From: Edward Fish <edward.r.fish@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: How do I write directly to a memory address?
Date: Fri, 11 Feb 2011 20:47:35 -0800 (PST)
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Date: 2011-02-11T20:47:35-08:00
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On Feb 2, 10:52=A0pm, Syntax Issues <syntax.iss...@gmail.com> wrote:
> I am planning to start learning lower-level programming with ada,
> however, I was unable to find a solid tutorial on writing directly to
> a memory address or interfacing with assembly. Does anyone know where
> I can find a reference to some tutorials/information? Below is an
> example of code I would like to be able to implement.
>

As others have replied using the 'Address attribute on a constrained
array
of your video's cell-type {attribute-character pair}is the way to go.

But if you're using GNAT you may have noticed that it doesn't allow
a straight "For Data'Address Use 16#000B_8000#;" because GNAT
uses a private type and not a derivative of Universal_Integer.

They recommend an implementation-dependent "to_Address" function,
but that would make things non-portable.

After some thought and some fiddling here's a portable, insofar as I
know,
method to convert an integer literal or constant (or even variable) to
an
address containing that value.

-- Address_Overlay.ads; Pragma pure may be added.
With System;
Package Address_Overlay is

   Type Address_Integer is Range 0..System.Memory_Size;

Private
End Address_Overlay;

-----  Address_Overlay.This.ads; an instantiation of
-----                             this provides the proper overlay
Generic
   Value : Address_Integer;
Package Address_Overlay.This is

   Address : Constant System.Address;		-- Overlay Address with Value.

Private
  Pragma Warnings (Off, "*overlay*");		-- Here we turn off the warning
   For Address'Address Use Value'Address;	-- about a constant
overlaying
   Pragma Import( Ada, Address );		-- a variable; as that is our
  Pragma Warnings (On, "*overlay*");		-- intention.
End Address_Overlay.This;

-----------
-- USAGE --
-----------
   Declare
      Package An_Address( 16#000C_8000#  );

      Data : Integer;
      For Data'Address Use An_Address.Address;
   Begin
	Data:=3D 4;
   End;