[Oberon] Volatile variables in Oberon

[Aubrey.McIntosh at alumni.utexas.net]

>From very old memory, I think that Modula-2 had a construct to allow
reading and writing from absolute memory addresses.  I don't know if a
Wirth compiler had this, or if it was from someone else.

Something similar to

VAR  memmap [ 100B ] : ARRAY 3 OF INTEGER;




On Sat, Jul 30, 2016 at 1:06 AM, Skulski, Wojciech <
skulski at pas.rochester.edu> wrote:

> Chris:
>
> > But Oberon variables are not mapped to registers that can be changed
> "from
> > the other end". The explicit operations SYSTEM.GET and SYSTEM.PUT are
> used
> > when you want to transfer data between a peripheral register (mapped to
> an
> > absolute memory location) and Oberon variables.
>
>  Pardon my C on this mailing list. The point I want to make is that it is
> ugly.
>
> Here is a sample of my C program where I am reading from an absolute
> memory location mapped to an FPGA register. The "target" is an integer,
> which is then used to retrieve a value from the FPGA. The address is not
> constant, but I can make it constant using a #define.
>
>  long target; /* long int holds addr, needs a typecast */
>  short value;
>  short *virt_saddr;     /* typed pointer to 16-bit short */
>
>  virt_saddr = (short *) target; /* convert target to pointer */
>  value = * virt_saddr;            /* read value from address   */
>
> I would prefer to write in C something like the following:
>
>  short value at address; /* address is constant, which is most often the
> case*/
>
> In Oberon it would be something like this:
>
>  CONST address = ....;
>   VAR value: INTEGER AT address; (* address must be constant*)
>
> Now the question, is this unreasonable?
>
> Wojtek
> --
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Aubrey McIntosh, Ph.D.
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