New input driver: Handykey's Twiddler as a joystick

[Arndt S. <ab...@sr...>]

Hi folks,

here is another input device driver for Linux 2.4 and ruby; it allows to
use Handykey's Twiddler (the original, RS232 version) as a joystick.

The Twiddler (http://www.handykey.com) is probably the most famous and
popular input device for wearable computers, many of which run Linux.
It is actually meant as a chording keyboard; you press multiple keys
simultaneously (a chord), and a keystroke is generated as soon as the
keys are released. To make this work, the Twiddler continuously sends
data packets describing the state of the keys up the serial line, and a
daemon process picks them up, analyzes them, consults a chord-to-keystroke
mapping table, and inserts the resulting keystrokes into the system. The
Linux version of this daemon currently does this using the TIOCSTI ioctl,
if a text console is active, or by means of the external program a2x,
if the current console is the one where the X server runs. This approach
has a couple of disadvantages; it would be much nicer if the Twiddler
was handled by a kernel module that could directly inject the keystrokes
into the system just like the keystrokes from other keyboards, perhaps
totally obviating the need for the daemon process, but at least obviating
the need to maintain different sets of chord-to-keystroke mappings for
X and console applications.

With this goal in mind, I went through the Linux 2.4. kernel sources to
look for ways how it could be done. This was when I first discovered
Vojtech's great new input framework that does not only make things like
this possible, but even easy. And after some more searching and browsing,
I came across The Linux Console Project and its Sourceforge pages.

So here is my first shot. The attached Twiddler driver, "twidjoy", is
quite simple, and it does a lot less than the chord-to-keystroke mapping
daemon mentioned above, but what it does is very useful in its own
right: It turns the Twiddler into a joystick with 2 analog axes (did I
mention that the Twiddler also has a built-in tilt sensor?!) and whopping
18 buttons! (And yes, all of them can be used with Unreal Tournament!)

The driver comes together with the appropriate additions to inputattach
which allow to select the "twidjoy" driver and check that the Twiddler is
present. I plan on writing another driver module, code-named "twidkbd",
that will then implement the Twiddler's standard chording behaviour
(i.e. generating keystrokes from button chords and mouse events from the
tilt sensor), so support for this upcoming driver is already present in
the submitted inputattach code, too. (My priority for the implementation
of "twidkbd" is a bit lower, though, because I will first try to improve
the Linux support for the newly available Twiddler2, but if someone
needs this and/or wants to help writing it, let me know.)

To develop the code, I checked out ruby from the CVS on Friday, modified
the file "utils/inputattach.c" and created "twidjoy.c" from the template
"linux/drivers/input/stinger.c". Since the relevant source files of the
input system in stock 2.4.5, 2.4.6, and ruby are mostly the same, I assume
that the driver should work with all of these Linux flavors. However, I
have myself only tried it with kernel 2.4.5 (stock, i.e. without ruby).
If the module passes your introspection and tests, I would very much like
to see it included into the 2.4 kernel branch.

Have fun with it!
Arndt

PS: This driver does NOT support the Twiddler2, which directly connects
to the PS/2 keyboard and mouse ports. The Twiddler2 does not need any
special drivers, so it works with Linux out of the box -- albeit not as
a 18 buttons joystick ;-)

-- 
Arndt Schoenewald <ab...@sr...>
Ostenhellweg 31, 44135 Dortmund, Germany
Tel: +49 231 556075