The virtual timer device virtualizes the hardware timer. The device provides services that other virtual devices can use to set the interrupt rate for the timer, and to disable I/O port trapping for the timer in a given virtual machine. The VTD provides the following services:
VTD_Begin_Min_Int_Period
VTD_Disable_Trapping
VTD_Enable_Trapping
VTD_End_Min_Int_Period
VTD_Get_Interrupt_Rate
VTD_Get_Real_Time
VTD_Get_Version
VTD_Update_System_Clock
The VTD_Update_System_Clock service is for exclusive use of the virtual machine manager (VMM).