Re: Type-safe low-level programming?

[Hans-Bernhard Broeker <broeker@physik.rwth-aachen.de>]

In comp.arch.embedded Bernd Trog <berndtrog@yahoo.com> wrote:

> Now I wonder, if its possible to make 'Set_Bit' type-safe *without*
> increasing the program memory size for every new register?

The only way I see is to drop the idea of passing the register and the
bit number inside that register as independent parameters --- they
aren't independent, and pretending they are is what causes your grief.
The need to introduce a comment to explain what Bit_A1 is supposed to
mean should have given you the hint.

What you need would be more like

  type Bit_Number is range 0 .. 8*16#ff#);

  Register_A : constant Address_Type := 1;

  Bit_A1 : constant Bit_Number := Register_A*8 + 4; 
  Bit_A2 : constant Bit_Number := Register_A*8 + 1;
[...]

and then

	procedure Set_Bit(Nr : in Bit_Number );

which would split up the Bit_Number in two parts, one to address a
register, the other to address bits inside that register.

Disclaimer: the above are the first lines of Ada code I ever edited in
my life, so don't trust them any further than you can throw your car
;-)
-- 
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.