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From: "John R. Strohm" <strohm@airmail.net>
Newsgroups: comp.lang.ada
Subject: Re: Help with Copying Shared Memory to Local
Date: Fri, 24 May 2002 13:43:09 -0700
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Date: 2002-05-24T13:43:09-07:00
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type x is record
    csr: byte;
    dr: byte;
end record;
for x use record at mod 2;
for x'size use 16;

Or something of that nature.

Admittedly, it has been a number of years since I last looked at Ada rep
specs.  The thing I remember most painfully was laying out the registers for
a Signetics 2681 DUART, and then writing a reusable device driver as a set
of four generics.

"Stephen Leake" <stephen.a.leake.1@gsfc.nasa.gov> wrote in message
news:ulma9mqnj.fsf@gsfc.nasa.gov...
> "John R. Strohm" <strohm@airmail.net> writes:
>
> > Ada representation specifications provide a clean way to
> > tell the compiler what kind of access to use,
>
> This is _not_ what rep spec say. They say how to lay out the bits in
> memory, not how to access them.
>
> > and most compilers were good about following the programmer's
> > wishes.
>
> Some compilers do "what you want", but there is _no_ guarrantee in the
> language for this.
>
> If you need a 16 bit access, use assembly code. Wrap it up in a
> low-level Ada subprogram, to make it easy to use.
>
> Yes, it feels inefficient and inelegant, but it is the best approach.
>
> --
> -- Stephe