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From: Vinzent 'Gadget' Hoefler <nntp-2004-04@t-domaingrabbing.de>
Newsgroups: comp.lang.ada
Subject: Re: Pass by reference
Date: Tue, 13 Apr 2004 12:26:57 +0200
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Date: 2004-04-13T12:26:57+02:00
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Simon Wright wrote:

>Vinzent 'Gadget' Hoefler <nntp-2004-04@t-domaingrabbing.de> writes:
>
>> Pat Rogers wrote:
>>=20
>> >If you made the type volatile that would also force by-reference.
>
>C.6(18): If a type is atomic or volatile and it is not a by-copy type,
                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Yes, but if I understand that part correctly, this is the point. The
register-type is just a simple Integer-type:

|package Registers is
|
|   type Reg_8 is mod 2**8;
|   type Reg_8_Access is access Reg_8;
|   [...]
|
|private
|
|   pragma Volatile (Reg_8);
|   [...]
|end Registers;

So although it is declared Volatile it is a by-copy type. Too bad.

>> Are you sure? I'm just looking at the assembly ouput of GNAT for a
>> procedure that takes a volatile type (memory mapped register) and it
>> does't seem so. Even worse, it optimizes the sequence of assignment
>> which I need for this register. If you have any idea how can I avoid
>> using access types to make it right, I'd be glad to hear it.
>
>I think you need to use inline assembler to be sure.

You must be kidding me, I'm just getting away from using assembler. :)
The old system was a 16-bit-CPU programmed entirely in assembly
language, now I am having MaRTE and Ada and you say, I should use
inline assembler instead? ;-)

Well, there is no general problem in here for me, but even with inline
assembler the fact remains that the procedure would need the _address_
of the register, and *not* its contents. So using inline assembler
wouldn't help in avoiding access types and if it doesn't, I won't need
it, because in that case the compiler generated code is just fine.

>And to be really sure you may need to use Volatile =3D> True on the
>call, I had to (this was GNAT/PowerPC, by the way).

I'm not sure if I understand... can I actually apply that pragma to a
call? Or am I missing something else?


Vinzent.