path: root/Documentation/usb/input.txt

			  Linux Input drivers v1.0
	       (c) 1999-2000 Vojtech Pavlik <vojtech@suse.cz>
			     Sponsored by SuSE
	    $Id: input.txt,v 1.4 2000/05/28 17:57:22 vojtech Exp $
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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@suse.cz>, or by paper mail: Vojtech Pavlik,
Ucitelska 1576, 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. However, in the current kernels, although it's
possibilities are much bigger, it's limited to USB devices only. This is
also why it resides in the drivers/usb subdirectory.

  The center of the input drivers is the input.o 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.o module.

1.2 Event handlers
~~~~~~~~~~~~~~~~~~
  These modules get events from input.o 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.o
	mousedev.o
	keybdev.o
	usbcore.o
	usb-[uo]hci.o
	hid.o

  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 that 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 hid.c
~~~~~~~~~~~
  Hid.c 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. The driver
doesn't support these yet, and a new, non-event interface should be designed
for them. If you have any of these devices (I don't), feel free to design
something and if it's good, it'll get into the driver.

  The usage of the hid.o 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.c and send me the syslog traces.

3.1.2 usbmouse.c
~~~~~~~~~~~~~~~~
  For embedded systems, for mice with broken HID descriptors and just any
other use when the big hid.c wouldn't be a good choice, there is the
usbmouse.c 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 hid.c
instead.

3.1.3 usbkbd.c
~~~~~~~~~~~~~~
  Much like usbmouse.c, this module talks to keyboards with a simplified
HIDBP protocol. It's smaller, but doesn't support any extra special keys.
Use hid.c instead if there isn't any special reason to use this.

3.1.4 wacom.c
~~~~~~~~~~~~~
  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 wmforce.c
~~~~~~~~~~~~~~~
  A driver for the Logitech WingMan Force joysticks, when connected via the
USB port. It works quite well, but there is no force feedback support yet,
because the interface to do that is a trade secret of Immersion Corp, and
even Logitech can't disclose it.

  Support for Logitech WingMan Force Wheel isn't present in this driver, but
if someone has the device, and is willing to cooperate, it should be a
matter of a couple days to add it.

3.2 Event handlers
~~~~~~~~~~~~~~~~~~
  Event handlers distribute the events from the devices to userland and
kernel, as needed.

3.2.1 keybdev.c
~~~~~~~~~~~~~~~
  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.c
~~~~~~~~~~~~~~~~
  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.c

  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 it's 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
GenPS/2 (Genius NetMouse/NetScroll) 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 GenPS/2 if you
want to use extra (up to 5) buttons. I'm not sure how much is GenPS/2 supported
in X, though.

3.2.3 joydev.c
~~~~~~~~~~~~~~
  Joydev implements v0.x and v1.x Linux joystick api, much like
drivers/char/joystick/joystick.c. See joystick-api.txt in the Documentation
subdirectory for details. Joydev does it on top of the input subsystem,
though. As soon as any USB 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.c
~~~~~~~~~~~~~
  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 usable 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
	...

3. Contacts
~~~~~~~~~~~
  This effort has it's 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.

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/joystick.txt).

  You can test the event devics with the 'evtest' utility available on the
input driver homepage (see the URL above).

5. Event interface
~~~~~~~~~~~~~~~~~~
  Should you want to add event device support into any application (X, gpm,
svgalib ...) I <vojtech@suse.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 movement, 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.