[Overview][Constants][Types][Procedures and functions][Variables][Index] | Reference for unit 'go32' (#rtl)

# get_rm_callback

Return real mode callback

## Declaration

Source position: go32.pp line 130

`function get_rm_callback(`
`pm_func: pointer;`
`const reg: trealregs;`
`var rmcb: tseginfo`
`):Boolean;`

## Description

Returns a unique real mode segment:offset address, known as a "real mode callback," that will transfer control from real mode to a protected mode procedure.

Parameters:

pm_func
  pointer to the protected mode callback function.
reg
  supplied registers structure.
rmcb
  buffer to real mode address of callback function.

Return values: True if successful, otherwise False.

Remark: | Callback addresses obtained with this function can be passed by a protected mode program for example to an interrupt handler, device driver, or TSR, so that the real mode program can call procedures within the protected mode program or notify the protected mode program of an event. The contents of the supplied regs structure is not valid after function call, but only at the time of the actual callback.

## Errors

Check the int31error variable.

## See also

free_rm_callback |  | Release real mode callback.

## Example

    {$ASMMODE ATT}
    {$MODE FPC}

    uses
            crt,
            go32;

    const
            mouseint = $33;

    var
            mouse_regs    : trealregs; external name '___v2prt0_rmcb_regs';
            mouse_seginfo : tseginfo;

    var
            mouse_numbuttons : longint;

            mouse_action : word;
            mouse_x, mouse_y : Word;
            mouse_b : Word;

            userproc_installed : Longbool;
            userproc_length : Longint;
            userproc_proc : pointer;

    procedure callback_handler; assembler;
    asm
       pushw %ds
       pushl %eax
       movw %es, %ax
       movw %ax, %ds

       cmpl $1, USERPROC_INSTALLED
       jne .LNoCallback
       pushal
       movw DOSmemSELECTOR, %ax
       movw %ax, %fs
       call *USERPROC_PROC
       popal
    .LNoCallback:

       popl %eax
       popw %ds

       pushl %eax
       movl (%esi), %eax
       movl %eax, %es: 42(%edi)
       addw $4, %es:46(%edi)
       popl %eax
       iret
    end;
    procedure mouse_dummy; begin end;

    procedure textuserproc;
    begin
            mouse_b := mouse_regs.bx;
            mouse_x := (mouse_regs.cx shr 3) + 1;
            mouse_y := (mouse_regs.dx shr 3) + 1;
    end;

    procedure install_mouse(userproc : pointer; userproclen : longint);
    var r : trealregs;
    begin
            r.eax := $0; realintr(mouseint, r);
            if (r.eax <> $FFFF) then begin
                    Writeln('No Microsoft compatible mouse found');
                    Writeln('A Microsoft compatible mouse driver is necessary ',
                            'to run this example');
                    halt;
            end;
            if (r.bx = $ffff) then mouse_numbuttons := 2
            else mouse_numbuttons := r.bx;
            Writeln(mouse_numbuttons, ' button Microsoft compatible mouse ',
                    ' found.');
            if (userproc <> nil) then begin
                    userproc_proc := userproc;
                    userproc_installed := true;
                    userproc_length := userproclen;
                    lock_code(userproc_proc, userproc_length);
            end else begin
                    userproc_proc := nil;
                    userproc_length := 0;
                    userproc_installed := false;
            end;
            lock_data(mouse_x, sizeof(mouse_x));
            lock_data(mouse_y, sizeof(mouse_y));
            lock_data(mouse_b, sizeof(mouse_b));
            lock_data(mouse_action, sizeof(mouse_action));

            lock_data(userproc_installed, sizeof(userproc_installed));
            lock_data(userproc_proc, sizeof(userproc_proc));

            lock_data(mouse_regs, sizeof(mouse_regs));
            lock_data(mouse_seginfo, sizeof(mouse_seginfo));
            lock_code(@callback_handler,
                    longint(@mouse_dummy)-longint(@callback_handler));
            get_rm_callback(@callback_handler, mouse_regs, mouse_seginfo);
            r.eax := $0c; r.ecx := $7f;
            r.edx := longint(mouse_seginfo.offset);
            r.es := mouse_seginfo.segment;
            realintr(mouseint, r);
            r.eax := $01;
            realintr(mouseint, r);
    end;

    procedure remove_mouse;
    var
            r : trealregs;
    begin
            r.eax := $02; realintr(mouseint, r);
            r.eax := $0c; r.ecx := 0; r.edx := 0; r.es := 0;
            realintr(mouseint, r);
            free_rm_callback(mouse_seginfo);
            if (userproc_installed) then begin
                    unlock_code(userproc_proc, userproc_length);
                    userproc_proc := nil;
                    userproc_length := 0;
                    userproc_installed := false;
            end;
            unlock_data(mouse_x, sizeof(mouse_x));
            unlock_data(mouse_y, sizeof(mouse_y));
            unlock_data(mouse_b, sizeof(mouse_b));
            unlock_data(mouse_action, sizeof(mouse_action));

            unlock_data(userproc_proc, sizeof(userproc_proc));
            unlock_data(userproc_installed, sizeof(userproc_installed));

            unlock_data(mouse_regs, sizeof(mouse_regs));
            unlock_data(mouse_seginfo, sizeof(mouse_seginfo));
            unlock_code(@callback_handler,
                    longint(@mouse_dummy)-longint(@callback_handler));
            fillchar(mouse_seginfo, sizeof(mouse_seginfo), 0);
    end;

    begin
            install_mouse(@textuserproc, 400);
            Writeln('Press any key to exit...');
            while (not keypressed) do begin
                    gotoxy(1, wherey);
                    write('MouseX : ', mouse_x:2, ' MouseY : ', mouse_y:2,
                            ' Buttons : ', mouse_b:2);
            end;
            remove_mouse;
    end.

Documentation generated on: Feb 26 2014