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From: stt@spock.camb.inmet.com (Tucker Taft)
Subject: Re: Pointers
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References: <3jki04$9bj@theopolis.orl.mmc.com>
Date: Mon, 13 Mar 1995 15:54:54 GMT
Date: 1995-03-13T15:54:54+00:00
List-Id: <comp.lang.ada>

Bob Gilbert (rgilbert@orl.mmc.com) wrote:
: In article 2er@gnat.cs.nyu.edu, dewar@cs.nyu.edu (Robert Dewar) writes:
: ->Jon, we have to ask why a simple address clause
: ->
: ->   for x use at ...
: ->
: ->does not work for you, since this is the obvious way of reading a specific
: ->memory address. You have to consult your implementor on how to represent
: ->address values, since this is obviously target dependent.

: Not to answer for Jon, but.....

: In my experience I have found several cases where the simple "for x use at .."
: will not work.  One problem is that with most comilers which support the 
: address clause, will perform a write to the memory location (initialization 
: I suppose) during elaboration.  This can cause problems with "read only" 
: addresses.  

In Ada 95, you can specify "pragma Import(Ada, <object-name>);"
which indicates that *no* default initialization is to be performed
by the compiler-generated code.  This is generally desirable when
using an address clause to associate a name with a machine register
of some sort.

Also, in Ada 95 there are language-defined functions for converting
integers to addresses.  Finally, the preferred syntax for
specifying the address of an object uses "for ...'Address use ...",
such as:

   for Console_Status_Register'Address use 
     System.Storage_Elements.To_Address(16#FFC0#);

The "for ... use at ..." syntax is still retained for upward 
compatibility reasons.

: -Bob

-Tucker Taft  stt@inmet.com
Intermetrics, Inc.