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linux-next/Documentation/input/input.txt
Linus Torvalds 1da177e4c3 Linux-2.6.12-rc2 
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!
2005-04-16 15:20:36 -07:00

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Linux Input drivers v1.0
(c) 1999-2001 Vojtech Pavlik <vojtech@ucw.cz>
Sponsored by SuSE
$Id: input.txt,v 1.8 2002/05/29 03:15:01 bradleym Exp $
----------------------------------------------------------------------------
0. Disclaimer
~~~~~~~~~~~~~
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your option)
any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc., 59
Temple Place, Suite 330, Boston, MA 02111-1307 USA
Should you need to contact me, the author, you can do so either by e-mail
- mail your message to <vojtech@ucw.cz>, or by paper mail: Vojtech Pavlik,
Simunkova 1594, Prague 8, 182 00 Czech Republic
For your convenience, the GNU General Public License version 2 is included
in the package: See the file COPYING.
1. Introduction
~~~~~~~~~~~~~~~
This is a collection of drivers that is designed to support all input
devices under Linux. While it is currently used only on for USB input
devices, future use (say 2.5/2.6) is expected to expand to replace
most of the existing input system, which is why it lives in
drivers/input/ instead of drivers/usb/.
The centre of the input drivers is the input module, which must be
loaded before any other of the input modules - it serves as a way of
communication between two groups of modules:
1.1 Device drivers
~~~~~~~~~~~~~~~~~~
These modules talk to the hardware (for example via USB), and provide
events (keystrokes, mouse movements) to the input module.
1.2 Event handlers
~~~~~~~~~~~~~~~~~~
These modules get events from input and pass them where needed via
various interfaces - keystrokes to the kernel, mouse movements via a
simulated PS/2 interface to GPM and X and so on.
2. Simple Usage
~~~~~~~~~~~~~~~
For the most usual configuration, with one USB mouse and one USB keyboard,
you'll have to load the following modules (or have them built in to the
kernel):
input
mousedev
keybdev
usbcore
uhci_hcd or ohci_hcd or ehci_hcd
usbhid
After this, the USB keyboard will work straight away, and the USB mouse
will be available as a character device on major 13, minor 63:
crw-r--r-- 1 root root 13, 63 Mar 28 22:45 mice
This device has to be created, unless you use devfs, in which case it's
created automatically. The commands to do create it by hand are:
cd /dev
mkdir input
mknod input/mice c 13 63
After that you have to point GPM (the textmode mouse cut&paste tool) and
XFree to this device to use it - GPM should be called like:
gpm -t ps2 -m /dev/input/mice
And in X:
Section "Pointer"
Protocol "ImPS/2"
Device "/dev/input/mice"
ZAxisMapping 4 5
EndSection
When you do all of the above, you can use your USB mouse and keyboard.
3. Detailed Description
~~~~~~~~~~~~~~~~~~~~~~~
3.1 Device drivers
~~~~~~~~~~~~~~~~~~
Device drivers are the modules that generate events. The events are
however not useful without being handled, so you also will need to use some
of the modules from section 3.2.
3.1.1 usbhid
~~~~~~~~~~~~
usbhid is the largest and most complex driver of the whole suite. It
handles all HID devices, and because there is a very wide variety of them,
and because the USB HID specification isn't simple, it needs to be this big.
Currently, it handles USB mice, joysticks, gamepads, steering wheels
keyboards, trackballs and digitizers.
However, USB uses HID also for monitor controls, speaker controls, UPSs,
LCDs and many other purposes.
The monitor and speaker controls should be easy to add to the hid/input
interface, but for the UPSs and LCDs it doesn't make much sense. For this,
the hiddev interface was designed. See Documentation/usb/hiddev.txt
for more information about it.
The usage of the usbhid module is very simple, it takes no parameters,
detects everything automatically and when a HID device is inserted, it
detects it appropriately.
However, because the devices vary wildly, you might happen to have a
device that doesn't work well. In that case #define DEBUG at the beginning
of hid-core.c and send me the syslog traces.
3.1.2 usbmouse
~~~~~~~~~~~~~~
For embedded systems, for mice with broken HID descriptors and just any
other use when the big usbhid wouldn't be a good choice, there is the
usbmouse driver. It handles USB mice only. It uses a simpler HIDBP
protocol. This also means the mice must support this simpler protocol. Not
all do. If you don't have any strong reason to use this module, use usbhid
instead.
3.1.3 usbkbd
~~~~~~~~~~~~
Much like usbmouse, this module talks to keyboards with a simplified
HIDBP protocol. It's smaller, but doesn't support any extra special keys.
Use usbhid instead if there isn't any special reason to use this.
3.1.4 wacom
~~~~~~~~~~~
This is a driver for Wacom Graphire and Intuos tablets. Not for Wacom
PenPartner, that one is handled by the HID driver. Although the Intuos and
Graphire tablets claim that they are HID tablets as well, they are not and
thus need this specific driver.
3.1.5 iforce
~~~~~~~~~~~~
A driver for I-Force joysticks and wheels, both over USB and RS232.
It includes ForceFeedback support now, even though Immersion
Corp. considers the protocol a trade secret and won't disclose a word
about it.
3.2 Event handlers
~~~~~~~~~~~~~~~~~~
Event handlers distrubite the events from the devices to userland and
kernel, as needed.
3.2.1 keybdev
~~~~~~~~~~~~~
keybdev is currently a rather ugly hack that translates the input
events into architecture-specific keyboard raw mode (Xlated AT Set2 on
x86), and passes them into the handle_scancode function of the
keyboard.c module. This works well enough on all architectures that
keybdev can generate rawmode on, other architectures can be added to
it.
The right way would be to pass the events to keyboard.c directly,
best if keyboard.c would itself be an event handler. This is done in
the input patch, available on the webpage mentioned below.
3.2.2 mousedev
~~~~~~~~~~~~~~
mousedev is also a hack to make programs that use mouse input
work. It takes events from either mice or digitizers/tablets and makes
a PS/2-style (a la /dev/psaux) mouse device available to the
userland. Ideally, the programs could use a more reasonable interface,
for example evdev
Mousedev devices in /dev/input (as shown above) are:
crw-r--r-- 1 root root 13, 32 Mar 28 22:45 mouse0
crw-r--r-- 1 root root 13, 33 Mar 29 00:41 mouse1
crw-r--r-- 1 root root 13, 34 Mar 29 00:41 mouse2
crw-r--r-- 1 root root 13, 35 Apr 1 10:50 mouse3
...
...
crw-r--r-- 1 root root 13, 62 Apr 1 10:50 mouse30
crw-r--r-- 1 root root 13, 63 Apr 1 10:50 mice
Each 'mouse' device is assigned to a single mouse or digitizer, except
the last one - 'mice'. This single character device is shared by all
mice and digitizers, and even if none are connected, the device is
present. This is useful for hotplugging USB mice, so that programs
can open the device even when no mice are present.
CONFIG_INPUT_MOUSEDEV_SCREEN_[XY] in the kernel configuration are
the size of your screen (in pixels) in XFree86. This is needed if you
want to use your digitizer in X, because its movement is sent to X
via a virtual PS/2 mouse and thus needs to be scaled
accordingly. These values won't be used if you use a mouse only.
Mousedev will generate either PS/2, ImPS/2 (Microsoft IntelliMouse) or
ExplorerPS/2 (IntelliMouse Explorer) protocols, depending on what the
program reading the data wishes. You can set GPM and X to any of
these. You'll need ImPS/2 if you want to make use of a wheel on a USB
mouse and ExplorerPS/2 if you want to use extra (up to 5) buttons.
3.2.3 joydev
~~~~~~~~~~~~
Joydev implements v0.x and v1.x Linux joystick api, much like
drivers/char/joystick/joystick.c used to in earlier versions. See
joystick-api.txt in the Documentation subdirectory for details. As
soon as any joystick is connected, it can be accessed in /dev/input
on:
crw-r--r-- 1 root root 13, 0 Apr 1 10:50 js0
crw-r--r-- 1 root root 13, 1 Apr 1 10:50 js1
crw-r--r-- 1 root root 13, 2 Apr 1 10:50 js2
crw-r--r-- 1 root root 13, 3 Apr 1 10:50 js3
...
And so on up to js31.
3.2.4 evdev
~~~~~~~~~~~
evdev is the generic input event interface. It passes the events
generated in the kernel straight to the program, with timestamps. The
API is still evolving, but should be useable now. It's described in
section 5.
This should be the way for GPM and X to get keyboard and mouse mouse
events. It allows for multihead in X without any specific multihead
kernel support. The event codes are the same on all architectures and
are hardware independent.
The devices are in /dev/input:
crw-r--r-- 1 root root 13, 64 Apr 1 10:49 event0
crw-r--r-- 1 root root 13, 65 Apr 1 10:50 event1
crw-r--r-- 1 root root 13, 66 Apr 1 10:50 event2
crw-r--r-- 1 root root 13, 67 Apr 1 10:50 event3
...
And so on up to event31.
4. Verifying if it works
~~~~~~~~~~~~~~~~~~~~~~~~
Typing a couple keys on the keyboard should be enough to check that
a USB keyboard works and is correctly connected to the kernel keyboard
driver.
Doing a cat /dev/input/mouse0 (c, 13, 32) will verify that a mouse
is also emulated, characters should appear if you move it.
You can test the joystick emulation with the 'jstest' utility,
available in the joystick package (see Documentation/input/joystick.txt).
You can test the event devices with the 'evtest' utility available
in the LinuxConsole project CVS archive (see the URL below).
5. Event interface
~~~~~~~~~~~~~~~~~~
Should you want to add event device support into any application (X, gpm,
svgalib ...) I <vojtech@ucw.cz> will be happy to provide you any help I
can. Here goes a description of the current state of things, which is going
to be extended, but not changed incompatibly as time goes:
You can use blocking and nonblocking reads, also select() on the
/dev/input/eventX devices, and you'll always get a whole number of input
events on a read. Their layout is:
struct input_event {
struct timeval time;
unsigned short type;
unsigned short code;
unsigned int value;
};
'time' is the timestamp, it returns the time at which the event happened.
Type is for example EV_REL for relative momement, REL_KEY for a keypress or
release. More types are defined in include/linux/input.h.
'code' is event code, for example REL_X or KEY_BACKSPACE, again a complete
list is in include/linux/input.h.
'value' is the value the event carries. Either a relative change for
EV_REL, absolute new value for EV_ABS (joysticks ...), or 0 for EV_KEY for
release, 1 for keypress and 2 for autorepeat.
6. Contacts
~~~~~~~~~~~
This effort has its home page at:
http://www.suse.cz/development/input/
You'll find both the latest HID driver and the complete Input driver
there as well as information how to access the CVS repository for
latest revisions of the drivers.
There is also a mailing list for this:
majordomo@atrey.karlin.mff.cuni.cz
Send "subscribe linux-input" to subscribe to it.
The input changes are also being worked on as part of the LinuxConsole
project, see:
http://sourceforge.net/projects/linuxconsole/
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