VITD: A VxD that Simulates an Interval Timer Device

VITD, the virtual interval timer device, is a VxD that creates an "interval timer"--a non-existent piece of hardware that enables programs to measure elapsed CPU time in a virtual machine. Applications communicate with VITD the same way they communicate with real hardware timers: through I/O ports.

VITD uses the following virtual machine manager (VMM) and virtual timer device (VTD) services:

_Allocate_Device_CB_Area

Fatal_Memory_Error

Install_Mult_IO_Handlers

Get_VM_Exec_Time

Set_VM_Time_Out

Cancel_Time_Out

Get_VM_Exec_Time

Call_Priority_VM_Event

Begin_Nest_Exec

End_Nest_Exec

Exec_Int

VTD_Get_Interrupt_Period

VTD_Begin_Min_Int_Period

VTD_End_Min_Int_Period

VTD_Get_Version

VTD_Get_Interrupt_Period

To use VITD, add the following line to the [386Enh] section of your SYSTEM.INI file:

DEVICE=VITD.386

Place VITD.386 in your Windows SYSTEM directory. Restart Microsoft(R) Windows(TM), and then create an MS-DOS virtual machine (VM). Inside the VM, run SAMPLE.EXE to set up an interval timer, run GETCOUNT.EXE to report the current interval timer count, and run DOSIT.EXE to register an interval timer interrupt handler that will start an interval timer. Wait until an interval timer interrupt occurs.

The interrupt usage, I/O addresses, status bits, and overall functioning of VITD is documented in the ITIMER.INC header file and the VITD.ASM source file. This sample code requires special VxD tools and include files; see the "VxD Tools" and "VxD Include Files" abstracts to copy these files to your development system. For more information on using the Microsoft Windows version 3.1 Device Driver Kit (DDK) files included on this CD, read the technical article "The VxD-Lite Mini-DDK." For more information on virtual device programming, see the DDK "Virtual Device Adaptation Guide."

VITD was built and tested under Microsoft Windows version 3.1.

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