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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: How do I disable elaboration code on this
Date: Sat, 09 Apr 2011 21:35:05 +0200
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Date: 2011-04-09T21:35:05+02:00
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Simon Wright <simon@pushface.org> writes on comp.lang.ada:
> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
>
>> Simon Wright <simon@pushface.org> writes on comp.lang.ada:
>>> Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org> writes:
>>>
>>>> On 04/09/2011 06:58 AM, Lucretia wrote:
>>>>> The following code will not compile no matter what I do. Basically, I
>>>>> want to write the startup code for Cortex-M3 in Ada with no assembly.
>>>>> So, the ISR code needs to be elaboration free as it's the first bit of
>>>>> code that would run on reset.
>>>>
>>>>>     Vector : constant Vectors :=
>>>>>       (Dummy'Access,
>>>>>        Dummy'Access,
>>>>>        Dummy'Access,
>>>>>        Dummy'Access);
>>>>>     pragma Convention (C, Vector);
>>>>>     for Vector'Address use Addr;
>>>>
>>>> I think what you need here is
>>>>
>>>> Vector : constant Vectors;
>>>> pragma Import (Ada, Vector);
>>>> for Vector'Address use Addr;
>>>>
>>>> since you don't want Vector to be initialized.
>>>>
>>>> Vector will not be initialized because you have pragma Import for it.
>>>>
>>>> Note that you don't need procedure Dummy.
>>>
>>> But the real code will have actual ISR procedures. OP is merely sparing
>>> us the unnecessary detail of the real ISRs.
>>
>> But the vector being in Flash ROM, the Ada code needs not and indeed may
>> not initialize it, so I think Jeffrey's reply is correct.  The pragma
>> Import and the address clause will make the actual vectors (in ROM)
>> visible to the Ada program.
>
> That would be true if the vector was built in a separate C or ASM
> file, but Luke wants to do the whole thing in Ada and then write it to
> Flash. See above: "Basically, I want to write the startup code for
> Cortex-M3 in Ada with no assembly."

The vector can and must be built and burned to Flash separately, by an
Ada program of course :) This Ada program cannot write to Flash, it can
only read the vector previously stored there with no elaboration and no
initialization.  This is very similar to things I did at Barco avionics
a few years ago (I even wrote the driver for writing to the particular
Flash device in pure Ada).

-- 
Ludovic Brenta.