DOS / Interrupts / 31


                           Interrupt 31h   Simulate Real Mode                            

Notes:  The CALL 5 entry point does a FAR jump to here

/*-------------------------------------------------------------------
SimulateRM_Int()

Allows protected-mode software to execute real-mode interrupts
such as calls to MS-DOS, MS-DOS TSRs, MS-DOS device drivers.

This function implements the "Simulate Real Mode Interrupt"
function of the DPMI specification v0.9 and later.

Parameters:

bIntNum
Number of the interrupt to simulate.

     lpCallStruct
        Call structure that contains params (register values)
        for bIntNum.

Return Value
SimulateRM_Int returns TRUE if it succeeded or FALSE if
it failed.

Comments
lpCallStruct is a protected-mode selector:offset address, not
a real-mode segment:offset address.
-------------------------------------------------------------------*/

BOOL FAR PASCAL SimulateRM_Int (BYTE bIntNum, LPRMCS lpCallStruct)
{
BOOL fRetVal = FALSE; // Assume failure

   _asm {
         push di
         mov ax, 0300h         ; DPMI Simulate Real Mode Interrupt
         mov bl, bIntNum       ; Number of the interrupt to simulate
         mov bh, 01h           ; Bit 0 = 1; all other bits must be 0
         xor cx, cx            ; No words to copy from PM to RM stack
         les di, lpCallStruct ; Real mode call structure
         int 31h               ; Call DPMI
         jc   END1              ; CF set if error occurred

         mov fRetVal, TRUE
     END1:
         pop di
        }
   return (fRetVal);
}

struct strRMCS
{
DWORD edi, esi, ebp, RESERVED, ebx, edx, ecx, eax;
WORD wFlags, es, ds, fs, gs, ip, cs, sp, ss;
};