get_rm_callback

   

Declaration:

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.

Notes: 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 int31error variable

See also:

free_rm_callback

Example

Program callback;

uses crt,
     go32;

const mouseint = $33;          

var mouse_regs    : trealregs;
    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;

{$ASMMODE DIRECT}
procedure callback_handler; assembler;
asm
   pushw %es
   pushw %ds
   pushl %edi
   pushl %esi
   cmpl $1, _USERPROC_INSTALLED
   je .LNoCallback
   pushal
   movw %es, %ax 
   movw %ax, %ds
   movw U_GO32_DOSMEMSELECTOR, %ax
   movw %ax, %fs  
   call *_USERPROC_PROC
   popal
.LNoCallback:

   popl %esi
   popl %edi
   popw %ds
   popw %es

   movl (%esi), %eax
   movl %eax, %es: 42(%edi) 
   addw $4, %es: 46(%edi)
   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 Mircosoft compatible mouse found');
        Write('A Mircosoft compatible mouse driver is');
        writeln(' necessary to run this example');
        halt;
     end;
     if (r.bx = $ffff) then mouse_numbuttons := 2
     else mouse_numbuttons := r.bx;
     Writeln(mouse_numbuttons, 
             ' button Mircosoft 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
           { write mouse state info }
           gotoxy(1, wherey);
           write('MouseX : ', mouse_x:2, 
                 ' MouseY : ', mouse_y:2, 
                 ' Buttons : ', mouse_b:2);
     end;
     remove_mouse;
end.