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Subject: Re: Cleanest Ada way to do this?
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Date: 2014-06-22T15:05:05-06:00
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On 22-Jun-14 10:51, Mike Silva wrote:
> I'd like some help on the cleanest, or most elegant, way to do this in Ada.
>  I'm writing to an LCD character display, in 4-bit mode, which requires writing
> an 8 bit character or command value as two 4 bit pieces.  The port (a memory
> address) being written to is 32 bits wide.  What I would like to be able to do
> is some form of this (not valid Ada, I know):
>
>   Port32(4..7) := Some_Char(4..7);
>   ..twiddle some other control bits..
>   Port32(4..7) := Some_Char(0..3);
>   ..twiddle some other control bits..
>
> Any thoughts?
>

Depends on the situation, I think; if there's a lot of them [ports] like 
say one for each 'character' you may be better off making a generic 
package to interface with it.

Package Parent is
   Type Segment is range 1..16 with Size => 4;
   Type LCD_Character is private;
   Type LCD_Handle is not null access LCD_Character;
Private
  Type Segment_Array is Array(Segment) of Boolean
     with Size => Segment'Last;
  Type LCD_Character is record
    Segments : Segment_Array;
  end record;
End Parent;

Generic
   Port_Address : in Address;
Package Parent.Port is
   Port : aliased LCD_Character with Volatile, Address => Port_Address;
End Parent.port;

With Parent.Port;
Package Display is
   Number_of_Segments : Constant Positive := 3;
   Type LCD_Array is Array(1..Number_of_Segments) of LCD_Handle;

   Display : constant LCD_Array;
Private
   Package Segment_1 is new Parent.Port( ######## );
   Package Segment_2 is new Parent.Port( ######## );
   Package Segment_3 is new Parent.Port( ######## );

   Display : constant LCD_Array:=
     ( 1 => Segment_1.Port, 2 => Segment_2.Port, 3 => Segment_3.Port );
End Display;

Or if it's a one-off type thing do it more directly:

LCD_Display : LCD_Character with Address => Port_Address;