## FILTER

[This is preliminary documentation and subject to change.]

### SUMMARY

WDM "value-add" filter drivers are covered in this sample.

FILTER is a code shell for a WDM filter ("value-add") driver. A filter driver loads either above or below the actual driver for a device object. The role of a filter driver is to add value by doing additional processing on the data passing through it. The source compiles into Filter.sys.

This is a working filter driver, but it does no value-add data processing. FILTER merely passes all data through it transparently. It implements all required Plug and Play and power functionality required of WDM drivers, making it a useful starting point for your value-add filter driver.

### BUILDING THE SAMPLE

Run the build command to build the sample. To make your device add the filter driver, edit the .inf installation script, following the directions in Inf.txt. Wdm.h is the only required header for this sample. Both checked and free builds are available.

FILTER works on all Windows® 2000 platforms, including X86 and Alpha. The code is also 64-bit compliant. The sample produces one binary, builds properly with Microsoft Visual C® 6.0, and supports Plug and Play and Power Management.

### TOOLS

No performance tools, debugger extensions, or control panel app extensions are available.

### RESOURCES

For more information, see Microsoft Developer Network and Microsoft Systems Journal articles by Walter Oney (November–December 1997) and Ervin Peretz (January 1999).

For tools and other resources, see http://www.microsoft.com/msj/.

### CODE TOUR

#### File Manifest

    File		Description

Filter.htm The documentation for this sample (this file) Makefile Makefile required to build the driver. Sources The generic file for building the code sample. Filter.c Initialization and dispatch code Pnp.c Plug and Play code Power.c Power Management code Util.c Utility functions Filter.h Header Filter.rc Resources file Inf.txt Guide to .inf installation script changes required to load Filter

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