The VTD provides the following services:
VTD_Begin_Min_Int_Period
VTD_Disable_Trapping
VTD_Enable_Trapping
VTD_End_Min_Int_Period
VTD_Get_Date_And_Time
VTD_Get_Interrupt_Period
VTD_Get_Real_Time
VTD_Get_Version
VTD_Update_System_Clock