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diff --git a/Documentation/input/input.rst b/Documentation/input/input.rst new file mode 100644 index 000000000..0eb61e67a --- /dev/null +++ b/Documentation/input/input.rst @@ -0,0 +1,281 @@ +.. include:: <isonum.txt> + +============ +Introduction +============ + +:Copyright: |copy| 1999-2001 Vojtech Pavlik <vojtech@ucw.cz> - Sponsored by SuSE + +Architecture +============ + +Input subsystem a collection of drivers that is designed to support +all input devices under Linux. Most of the drivers reside in +drivers/input, although quite a few live in drivers/hid and +drivers/platform. + +The core of the input subsystem 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: + +Device drivers +-------------- + +These modules talk to the hardware (for example via USB), and provide +events (keystrokes, mouse movements) to the input module. + +Event handlers +-------------- + +These modules get events from input core 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. + +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 + usbcore + uhci_hcd or ohci_hcd or ehci_hcd + usbhid + hid_generic + +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 usually created automatically by the system. The commands +to 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. + +Detailed Description +==================== + +Event handlers +-------------- + +Event handlers distribute the events from the devices to userspace and +in-kernel consumers, as needed. + +evdev +~~~~~ + +``evdev`` is the generic input event interface. It passes the events +generated in the kernel straight to the program, with timestamps. The +event codes are the same on all architectures and are hardware +independent. + +This is the preferred interface for userspace to consume user +input, and all clients are encouraged to use it. + +See :ref:`event-interface` for notes on API. + +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 + ... + +There are two ranges of minors: 64 through 95 is the static legacy +range. If there are more than 32 input devices in a system, additional +evdev nodes are created with minors starting with 256. + +keyboard +~~~~~~~~ + +``keyboard`` is in-kernel input handler and is a part of VT code. It +consumes keyboard keystrokes and handles user input for VT consoles. + +mousedev +~~~~~~~~ + +``mousedev`` is a hack to make legacy 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. + +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 older programs +that do not handle hotplug 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. + +joydev +~~~~~~ + +``joydev`` implements v0.x and v1.x Linux joystick API. See +:ref:`joystick-api` 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 in legacy range, and additional nodes with minors +above 256 if there are more joystick devices. + +Device drivers +-------------- + +Device drivers are the modules that generate events. + +hid-generic +~~~~~~~~~~~ + +``hid-generic`` is one of 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/hid/hiddev.rst +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. + +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. + +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. + +psmouse +~~~~~~~ + +This is driver for all flavors of pointing devices using PS/2 +protocol, including Synaptics and ALPS touchpads, Intellimouse +Explorer devices, Logitech PS/2 mice and so on. + +atkbd +~~~~~ + +This is driver for PS/2 (AT) keyboards. + +iforce +~~~~~~ + +A driver for I-Force joysticks and wheels, both over USB and RS232. +It includes Force Feedback support now, even though Immersion +Corp. considers the protocol a trade secret and won't disclose a word +about it. + +Verifying if it works +===================== + +Typing a couple keys on the keyboard should be enough to check that +a 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 :ref:`joystick-doc`). + +You can test the event devices with the ``evtest`` utility. + +.. _event-interface: + +Event interface +=============== + +You can use blocking and nonblocking reads, and 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 moment, EV_KEY for a keypress or +release. More types are defined in include/uapi/linux/input-event-codes.h. + +``code`` is event code, for example REL_X or KEY_BACKSPACE, again a complete +list is in include/uapi/linux/input-event-codes.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. + +See :ref:`input-event-codes` for more information about various even codes. |