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Tried
the Inpout32.dll..? then Learn how Inpout32.dll does the things. This
brief tutorial explains about the working of Inpout32.dll in simple
steps, with the help of a flow chart. This could help you much if you
want to modify the Inpout32 dll source code
If you don't know what is Inpout32.dll, please read it here and then continue.
How it works
The outstanding feature of Inpout32.dll is , it can work with all the
windows versions without any modification in user code or the DLL
itself. This tutorial describes how it is achieved, what programming
methods used, what are the APIs used, etc.... The Dll will check the
operating system version when functions are called, and if the operating
system is WIN9X, the DLL will use _inp() and _outp functions for
reading/writing the parallel port. On the other hand, if the operating
system is WIN NT, 2000 or XP, it will install a kernel mode driver and
talk to parallel port through that driver. The user code will not be
aware of the OS version on which it is running. This DLL can be used in
WIN NT clone operating systems as if it is WIN9X. The flow chart of the
program is given below.
The two important building blocks of this program are
1) A kernel mode device driver embedded in the DLL in binary form
2) The DLL itself
Kernel mode driver Hwinterface.sys
The source code of Hwinterface.sys kernel mode driver is located in
"kernel_mode_driver_source" directory. Where "hwinterfacedrv.c" is the
main application source file. Three functions implemented in the driver
are
1) DriverEntry() , Called when driver is loaded. Creates device object and symbolic links.
2) hwinterfaceUnload(), Called when driver is unloaded, performs clean up
3) hwinterfaceDeviceControl(), handles calls made through
DeviceIOControl API. Performs reading writing to the parallel port
according to the control code passed.
The DLL Inpout32
The functions in the DLL are implemented in two source files,
"inpout32drv.cpp" and "osversion.cpp". osversion.cpp checks the version
of operating system. "inpout32drv.cpp" does installing the kernel mode
driver, loading it , writing/ reading parallel port etc... The two
functions exported from inpout32.dll are
1) Inp32(), reads data from a specified parallel port register.
2) Out32(), writes data to specified parallel port register.
the other functions implemented in Inpout32.dll are
1) DllMain(), called when dll is loaded or unloaded. When the dll is
loaded , it checks the OS version and loads hwinterface.sys if needed.
2) Closedriver(), close the opened driver handle. called before unloading the driver.
3) Opendriver(), open a handle to hwinterface driver.
4) inst() , Extract 'hwinterface.sys' from binary resource to
'systemroot\drivers' directory and creates a service. This function is
called when 'Opendriver' function fails to open a valid handle to
'hwinterface' service.
5) start() , starts the hwinterface service using Service Control Manager APIs.
6) SystemVersion() Checks the OS version and returns appropriate code.
What is hwinterface.ocx ActiveX control
It is an activex control with same features of Inpout32.dll. It can be
used either with VC++ or VB. But it gives great convenience when used
with VB. Data can be written to parallel port using Outport method and
can be read using Inport method.
Download Inpout32.dll and source code here
Useful links
Windows NT/Windows 2000/WDM Driver FAQ by Jamie E. Hanrahan
Programming Windows Driver Model by Walter Oney
Details of all the APIs used is available at MSDN Online
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