[fpc-devel] Freepascal in microcontrollers

[Vinzent Hoefler]

On Wednesday 27 February 2008 09:44, Michael Schnell wrote:

> You can avoid cryptic language constructs in the main source code.

Or you can avoid cryptic languages altogether. :D

> I did not yet use the preprocessor in Pascal but a standard way to
> access memory mapped ports in C is something like this (from the top
> of my head):
>
>
> #define _port = 0x87
>
> #define ByteIO(p) *(((volatile unsigned char)*)(p))
>
> #define port=ByteIO(_port)

-- 8< -- snip --

with Interfaces;
with System.Storage_Elements;

procedure Foo is
   --
   -- Declare a reusable volatile 8 bit IO port type.
   --
   type IO_Port is new Integer range 0 .. 255;
   for IO_Port'Size use 8;    -- 8 bits, of course.
   pragma Atomic (IO_Port);   -- Sort of superfluous here.
   pragma Volatile (IO_Port);

   -- Make address conversions directly visible,
   -- but only inside "Foo" here.
   use System.Storage_Elements;

   -- Now declare a (volatile) IO port variable,
   -- and tell its address.
   My_Port : IO_Port;
   for My_Port'Address use To_Address (16#87#);
begin
   -- Assign the 0x55 value to the 0x87 address.
   My_Port := 2#01010101#;
end Foo;

-- 8< -- snip --

Although it's a whole lot of declarations for this simple:

-- 8< --

_ada_foo:
.LFB3:
        movb    $85, 135
        ret
.LFE3:

-- 8< --

So, given the right choices, neither C, nor a preprocessor is needed.

And hell, preprocessors sometimes are even forbidden for a particular 
project. If you want to verify code you need the code which turns up 
after being preprocessed anyway.


Vinzent.