From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Subject: Re: Forcing GNAT to use 32-bit load/store instructions on ARM?
Date: Sat, 05 Jul 2014 02:18:22 +0200
Date: 2014-07-05T02:18:22+02:00 [thread overview]
Message-ID: <c1ouibF1sfU1@mid.individual.net> (raw)
In-Reply-To: <c1osvbFuc0jU1@mid.individual.net>
On 14-07-05 01:51 , Niklas Holsti wrote:
> On 14-07-02 09:30 , Simon Wright wrote:
>> daniel.dmk@googlemail.com writes:
>>
>>> Thanks for this suggestion, I'll define the reserved bits in the
>>> register, and use static checks to enforce that they are not modified
>>> from their reset value in the code.
>>
>> You could use something like
>>
>> type Reserved_Bit is range 0 .. 0 with Size => 1;
>> type Reserved is array (Natural range <>) of Reserved_Bit
>> with Component_Size => 1;
>>
>> ...
>>
>> type T is record
>> A : Boolean; -- at bit 0
>> Res : Reserved (1 .. 6);
>> B : Boolean; -- at bit 7
>> end record with Size => 8;
>>
>> (with representation clauses as indicated)
>
> That has two potential problems...
>
> - First, even if Reserved_Bit is constrained to a single value (0), that
> does not mean that an uninitialized variable or component of this type
> will have that value. It will still have to be assigned the value zero,
> to be sure of having that value.
>
> - Second, if you read the value of the control register into a variable
> of type T, and some of the reserved bits read as 1 (which is not quite
^^^
(Delete the word "not", above -- it is quite possible that some reserved
bits read as 1, although they should be written with zero.)
> possible), these Reserved_Bit components will now, very probably, have
> an invalid representation, which is a nasty state.
>
> For these reasons, I would define Reserved_Bit as range 0 .. 1 and
> perhaps provide the default value (others => 0) for the Res component.
>
--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .
prev parent reply other threads:[~2014-07-05 0:18 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-30 22:11 Forcing GNAT to use 32-bit load/store instructions on ARM? daniel.dmk
2014-06-30 23:41 ` Jeffrey Carter
2014-07-01 12:06 ` Simon Clubley
2014-07-01 15:44 ` Niklas Holsti
2014-07-01 17:26 ` Simon Clubley
2014-07-01 17:18 ` Simon Wright
2014-07-01 19:43 ` Simon Wright
2014-07-01 17:28 ` Jeffrey Carter
2014-07-01 0:55 ` anon
2014-07-01 4:30 ` Niklas Holsti
2014-07-01 8:11 ` Dmitry A. Kazakov
2014-07-01 12:09 ` Simon Clubley
2014-07-01 12:20 ` Dmitry A. Kazakov
2014-07-01 17:00 ` Simon Clubley
2014-07-01 19:36 ` Dmitry A. Kazakov
2014-07-01 20:08 ` Simon Clubley
2014-07-02 22:24 ` Randy Brukardt
2014-07-06 20:40 ` MatthiasR
2014-07-07 0:25 ` Simon Clubley
2014-07-07 22:38 ` Randy Brukardt
2014-07-08 6:51 ` Simon Wright
2014-07-10 11:47 ` Simon Wright
2014-07-10 13:06 ` Simon Clubley
2014-07-11 18:05 ` Simon Wright
2014-07-11 20:22 ` Simon Clubley
2014-07-08 8:50 ` Brian Drummond
2014-07-08 12:12 ` Simon Clubley
2014-07-08 13:26 ` G.B.
2014-07-08 17:13 ` Simon Clubley
2014-07-08 15:36 ` Adam Beneschan
2014-07-08 15:40 ` Adam Beneschan
2014-07-08 20:34 ` Randy Brukardt
2014-07-09 7:31 ` Dmitry A. Kazakov
2014-07-10 0:11 ` Simon Clubley
2014-07-20 11:35 ` MatthiasR
2014-07-20 15:49 ` Simon Clubley
2014-07-26 11:05 ` MatthiasR
2014-08-10 11:20 ` MatthiasR
2014-07-01 12:03 ` Simon Clubley
2014-07-01 19:52 ` daniel.dmk
2014-07-01 20:40 ` Simon Clubley
2014-07-01 20:55 ` Simon Clubley
2014-07-01 21:01 ` Niklas Holsti
2014-07-01 21:20 ` Simon Clubley
2014-07-01 22:38 ` Niklas Holsti
2014-07-02 16:49 ` Simon Clubley
2014-07-01 21:55 ` daniel.dmk
2014-07-02 7:30 ` Simon Wright
2014-07-02 18:52 ` daniel.dmk
2014-07-04 23:51 ` Niklas Holsti
2014-07-05 0:18 ` Niklas Holsti [this message]
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