VWatchD: Illustrates the Basic Structure of a VxD

Revised: February 1993

VWatchD, the virtual watch device, demonstrates the basic
structure of a VxD. TEST.EXE is an MS-DOS(R) application
 that calls the VWatchD V86 API entry.

VWatchD uses the following virtual machine manager (VMM)
services:

>  _Allocate_Device_CB_Area
>  Get_System_Time
>  Fatal_Memory_Error


To build VWatchD:

You will need Microsoft(R) Macro Assembler version 6.0 or
higher, as well as some special tools and include files;
see the "VxD Tools" and "VxD Include Files" abstracts to
 copy these files to your development system. Configure
your development environment as described in the "VxD-Lite
Mini-DDK" technical article on the Microsoft Developer
Network CD.

If you have the Windows(TM) version 3.1 Device Driver Kit
(DDK), you can build its version of VWatchD using the DDK-
supplied MASM5.EXE (a special version of Macro Assembler
version 5.10). Note that the DDK samples require a
specific structure for the source and include
subdirectories, whereas the corresponding samples in the
"VxD-Lite Mini-DDK" utilize the INCLUDE environment
variable to give you more flexibility in structuring your
development files.


To execute VWatchD:

1.  Run VWATCHD.EXE from the MS-DOS prompt before starting
Windows. When enhanced-mode Windows starts up, the VxD
will load automatically. Thus, you do not need to modify
the SYSTEM.INI file to load this VxD. VWatchD will
automatically load each time you start Windows until you
reboot your computer; once rebooted, the stub loader is
cleared from memory and the VxD will not load.

If you prefer to have Windows load the VxD without first
executing it from the MS-DOS prompt, rename VWATCHD.EXE to
VWATCHD.386 and move it to the Windows SYSTEM
subdirectory. Add the line DEVICE=VWATCHD.386 to the
[386Enh] section of the SYSTEM.INI file.

2.  Run Windows in enhanced mode. The code responsible for
self-loading the VxD is in the VXDSTUB.ASM file and is
linked into the final VxD file by the STUB 'VXDSTUB.EXE'
module definition (.DEF) file statement. When executed
 from the MS-DOS prompt, the VxDStub hooks Interrupt 2Fh,
terminates, and stays resident. When Microsoft Windows
initializes itself, the TSR responds to the Interrupt 2Fh,
AX=1605h broadcast and returns a structure that causes the
VxD to be loaded. This technique is discussed in the "TSR
Support in Microsoft Windows Version 3.1" technical
article on the Microsoft Developer Network CD.
 
3.  Start an MS-DOS virtual machine (VM) and run TEST.EXE
in that VM. TEST.EXE will ask the VWatchD device when the
VM was created and report that number in milliseconds.

4.  Start another MS-DOS VM and run TEST in that VM. Note
the older "birthday" of the second VM.

You should set up a debug terminal to see the debugging
output produced by VWatchD. Run the debugging version of
WIN386.EXE.

VWatchD was built and tested under Microsoft Windows
version 3.1 using Microsoft MASM versions 6.0 and 6.1 and
the tools and include files provided in the "VxD-Lite Mini-
DDK."

KEYWORDS: PR-CD1; CD3 (revised)

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