INT 7F - Alloy NTNX - GET SYSTEM FLAGS
        AH = 0Ah
        CL = 00h
        ES:DI -> buffer for system flags (see below)
Return: ES:DI buffer filled
Notes:  on a slave, only the NX_Busy flag is returned
        all three flags are at fixed positions, so this function only needs to
          be called once
        an interrupt handler should only perform DOS or device accesses when
          all three flags are 00h

Format of system flags:
Offset  Size    Description
 00h    DWORD   pointer to NX_Busy flag (nonzero when communicating with users)
 04h    DWORD   pointer to device driver busy flag
 08h    DWORD   pointer to InTimer flag