TOPIC:

program gpio;

{$mode objfpc}{$H+}

uses
  Classes,SysUtils, baseUnix, Unix
  { you can add units after this };

  const
    MAP_SIZE: size_t = 4096;
    MAP_MASK: off_t = 4095; // MAP_SIZE - 1;
    CONTROL: LongWord =     $56000000;
   // CONTROLBASE = $56000000;

   // CONTROLOFFSET = 14;//$10;

  type
    PCardinal = ^Cardinal;
    PWord = ^Word;
    PByte = ^Byte;

  var
    _memFile: Integer;
    _map_base: Pointer;
    _virtAddr: Pointer;


begin
  try

   _memFile := fpOpen('/dev/mem', O_RDWR or O_SYNC);

   if _memFile < 0 then
   begin
     WriteLn('Error opening system memory');
     Exit;
   end;

   WriteLn('_memFile:' + IntToStr(_memFile));

   _map_base := FpMmap( nil, MAP_SIZE, PROT_READ or PROT_WRITE, MAP_SHARED, _memFile, CONTROL and (not MAP_MASK) ); //produces exception
// if MAP_SIZE is $56000000 and CONTROL = 0 then everything works 

    if Integer(_map_base) < 0 then
    begin
      WriteLn('Error maping memory, error:' + IntToStr(fpGetErrNo));
      Exit;
    end;


    WriteLn('_map_base:'+ IntToStr(Cardinal(_map_base)));

   
   _virtAddr := Pointer(Cardinal(_map_base) + 14); //CONTROL and MAP_MASK

   WriteLn('VirtAddr:'+ IntToStr(Cardinal(_VirtAddr)));

   WriteLn('Byte:' + IntToStr(PByte(_virtAddr)^));
   WriteLn('Word:' + IntToStr(PWord(_virtAddr)^));
   WriteLn('Cardinal:' + IntToStr(PCardinal(_virtAddr)^));


  finally
    fpMUnmap(_map_base,MAP_SIZE);

    if _memFile > 0 then
        fpClose(_memFile);

  end;
end.