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From: r_c_chapman@my-deja.com
Newsgroups: comp.lang.ada
Subject: Help with Atomic_Components and whole array assignment
Date: Mon, 22 Jan 2001 11:22:42 GMT
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Date: 2001-01-22T11:22:42+00:00
List-Id: <comp.lang.ada>

Having a slight confusion over the use of array aggregate assignments
with Atomic_Components.

We have a device which _has_ to be accessed use byte-wide load
and store instructions only (it's an autostore NOVRAM...), so we
have an array of bytes declared, thus:

  type Byte is range 0 .. 255;
  for Byte'Size use 8;
  for Byte'Alignment use 1;
  type Index is range 0 .. 4; -- for argument's sake!
  type Byte_Array is array (Index) of Byte;
  pragma Volatile (Byte_Array);
  pragma Atomic_Components (Byte_Array);

  A : Byte_Array;
  for A'Address use ...

all fine so far.  When we initialise this array, thus:

  A := Byte_Array'(others => 0);

compiler A generates 1 Word-sized store and 1 Byte-sized store.
(Target is PowerPC by the way.)
Compiler B (or should that be "G" :-) ) generates similar code on IA32.

Can anyone confirm this is indeed acceptable behaviour?

PS...Yes I know the Byte should probably be modular, but this is SPARK,
and we haven't got them implemented (yet... :-) )
 Thanks,
  Rod




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