Sysinternals Freeware - Mark Russinovich & Bryce Cogswell

Ctrl2Cap for Windows NT

Copyright 1997-2005 Mark Russinovich
Last Updated: May 2, 2005 Version 3.0


Ctrl2cap is a kernel-mode device driver that filters the system's keyboard class driver in order to convert caps-lock characters into control characters. People like myself that migrated to NT from UNIX are used to having the control key located where the caps-lock key is on the standard PC keyboard, so a utility like this is essential for our editing well-being.

Ctrl2cap works on NT 4.0 and higher, as well as 64-bit Windows XP and Window Server 2003. See Ctrl2cap for Windows 9x for a version that works on Windows 95/98.

Installation and Use

Install Ctrl2cap running the command "ctrl2cap /install" from the directory into which you've unzipped the Ctrl2cap files. To uninstall type "ctrl2cap /uninstall". If you are running on 64-bit Windows run ctrl2cap64.exe instead.

Building Ctrl2cap

Ctrl2cap requires ntddkbd.h from the ddk\src\input\inc directory, so you must first copy that file to the ctrl2cap directory. To build a standard NT 4 driver type "buildnt4" and to build a Win2K WDM driver type "buildnt5". Output files are placed in the \release subdirectory.

How Ctrl2cap Works

On NT 4 Ctrlcap is actually quite trivial. It simply attaches itself to the keyboard class driver so that it will catch keyboard read requests. For each request, it posts an I/O completion callback, at which point it takes a peek at the scancode that is being returned. If it happens to be a caps-lock, ctrl2cap changes it into a left-control.

On Win2K Ctrl2cap is a WDM filter driver that layers in the keyboard class device's stack above the keyboard class device. This is in contrast to the Win2K DDK's kbfiltr example that layers itself between the i8042 port device and the keyboard class device. I chose to layer on top of the keyboard class device for several reasons:

The disadvantage of my approach is (and this an advantage or disadvantage depending on your point of view):

In this particular case I felt that the advantages outweigh the disadvantages. However, before you model a Win2K keyboard filter on Ctrl2cap I strongly suggest that you study the kbfiltr example from the Win2K DDK. Kbfiltr's interception point in the key input sequence makes it very easy for kbfiltr to inject keystrokes into the input stream, something that would be more difficult using the Ctrl2cap source base.

More Information

For more information on writing filter drivers (drivers that attach themselves to other drivers so that they can see their input and/or output), here are sources to check out:

Download Ctrl2cap (6KB)

Download Ctrl2cap Plus Source (65KB)

Back to Top