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    SubjectRe: [PATCH 2/4] Documentation: Add evdev type and code definitions
    On Tue, Dec 14, 2010 at 01:21:10PM -0800, Chase Douglas wrote:
    > This commit adds the file Documentation/input/evdev-codes.txt.
    >
    > Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
    > ---
    > Documentation/input/evdev-codes.txt | 160 +++++++++++++++++++++++++++++++++++
    > 1 files changed, 160 insertions(+), 0 deletions(-)
    > create mode 100644 Documentation/input/evdev-codes.txt
    >
    > diff --git a/Documentation/input/evdev-codes.txt b/Documentation/input/evdev-codes.txt
    > new file mode 100644
    > index 0000000..69c810f
    > --- /dev/null
    > +++ b/Documentation/input/evdev-codes.txt
    > @@ -0,0 +1,160 @@
    > +The evdev protocol uses a map of types and codes to express input device values
    > +to userspace. This document describes the types and codes and how and when they
    > +may be used.
    > +
    > +Types:
    > +==========
    > +Types are groupings of codes under a logical input construct. Each type has a
    > +set of applicable codes to be used in generating events. See the Codes section
    > +for details on valid codes for each type.
    > +
    > +* EV_SYN:
    > + - Used as markers to separate events. Events may be separated in time or in
    > + space, such as with the multitouch protocol.
    > +* EV_KEY:
    > + - Used to describe keyboard and other key-like input events.
    > +* EV_REL:
    > + - Used to describe relative input events, e.g. moving the mouse 5 units to the
    > + left.
    > +* EV_ABS:
    > + - Used to describe absolute input events, e.g. describing the coordinates of a
    > + touch on a touchscreen.
    > +* EV_MSC:
    > + - Used to describe miscellaneous input events that do not fit into other
    > + types.
    > +* EV_SW:
    > + - Used to describe binary state input switches.
    > +* EV_LED:
    > + - Used to turn LEDs on devices on and off.
    > +* EV_SND:
    > + - Used to output sound to devices.
    > +* EV_REP:
    > + - Used for autorepeating devices.
    > +* EV_FF:
    > + - Used to send force feedback commands to an input device.
    > +* EV_PWR:
    > + - A special type for power button and switch input.
    > +* EV_FF_STATUS:
    > + - Used to receive force feedback device status.
    > +
    > +Codes:
    > +==========
    > +Codes define the precise type of event.
    > +
    > +EV_SYN Codes:
    > +----------
    > +EV_SYN event values are undefined. Their usage is
    > +defined only by when they are sent in the evdev event stream.
    > +
    > +* SYN_REPORT:
    > + - Used to synchronize and separate events in time. For example, motion of a
    > + mouse may set the REL_X and REL_Y values for one motion, then emit a
    > + SYN_REPORT. The next motion will emit more REL_X and REL_Y values and send
    > + another SYN_REPORT.
    > +* SYN_CONFIG:
    > + - TBD
    > +* SYN_MT_REPORT:
    > + - Used to synchronize and separate touch events. See the
    > + multi-touch-protocol.txt document for more information.
    > +
    > +EV_KEY:
    > +----------
    > +EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
    > +to represent the 'A' key on a keyboard. When a key is depressed, an event with
    > +the key's code is emitted with value 1. When the key is depressed, an event is
    > +emitted with value 0. In general, KEY_<name> is used for keyboard keys, and
    > +BTN_<name> is used for other types of momentary switch events.

    repeat keys have value 2, might want to add this here.

    > +
    > +A few EV_KEY codes have special meanings:
    > +
    > +* BTN_TOOL_<name>, BTN_TOUCH:
    > + - These codes are used in conjunction with input trackpads, tablets, and
    > + touchscreens. These devices may be used with fingers, pens, or other tools.
    > + When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
    > + code should be set to a value of 1. When the tool is no longer interacting
    > + with the input device, the BTN_TOOL_<name> code should be reset to 0. All
    > + trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
    > + code when events are generated. For non-tablet devices, the tool is usually
    > + BTN_TOUCH.

    BTN_TOUCH is used as proximity delimiter. e.g. wacom sends BTN_TOOL_PEN when
    the pen comes into proximity and (in addition) BTN_TOUCH when the pen
    actually touches the tablet. synaptics does the same IIRC except that it
    doesn't support hovering, so BTN_TOOL_FINGER and BTN_TOUCH are always
    set/unset in the same EV_SYN frame.


    > +
    > +* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
    > + - These codes denote one, two, three, and four finger interaction on a
    > + trackpad or touchscreen. For example, if the user uses two fingers and moves
    > + them on the touchpad in an effort to scroll content on screen,
    > + BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
    > + Note that these codes and the BTN_TOOL_<name> and BTN_TOUCH codes are
    > + orthogonal in purpose. A trackpad event generated by finger touches should
    > + generate events for one code from each group.
    > +
    > +* KEY_SUSPEND, KEY_POWER:
    > + - These codes are reserved for the EV_PWR type.
    > +
    > +EV_REL:
    > +----------
    > +EV_REL events describe relative changes in a property. For example, a mouse may
    > +move to the left by a certain number of units, but its absolute position in
    > +space is unknown. If the absolute position is known, EV_ABS codes should be used
    > +instead of EV_REL codes.
    > +
    > +A few EV_REL codes have special meanings:
    > +
    > +* REL_WHEEL, REL_HWHEEL:
    > + - These codes are used for vertical and horizontal scroll wheels,
    > + respectively.

    I'm not sure they're special, other than in X where we still treat them as
    buttons by convention. It's good to describe them here, just in case, but I
    wouldn't call that a "special meaning".

    > +
    > +EV_ABS:
    > +----------
    > +EV_ABS events describe absolute changes in a property. For example, a touchpad
    > +may emit coordinates for a touch location.
    > +
    > +A few EV_ABS codes have special meanings:
    > +
    > +* ABS_PRESSURE:
    > + - Used to describe the pressure of a touch interaction on an input device.

    again, that's not really special IMO. it pretty much does what it says on
    the box :)

    fwiw, I know that even though the documentation should be enough as-is,
    having a few simple examples are always really useful to form the picture in
    one's head. especially for newcomers who don't understand the basic concepts
    yet.

    just something like:
    "for example, an absolute device moving to a new position and pressing and
    releasing a button may send events like this:
    code value
    -----------------------
    ABS_X 10
    ABS_Y 100
    BTN_LEFT 1
    EV_SYN SYN_REPORT
    BTN_LEFT 0
    EV_SYN SYN_REPORT

    This immediately makes it obvious that buttons and axes can be mixed in the
    same frame. you may want to also point to a few tools that show the event
    stream (evtest comes to mind as the most widely distributed).

    Cheers,
    Peter

    > +* ABS_DISTANCE:
    > + - Used to describe the distance of a tool from an interaction surface. This
    > + should only be used while the tool is in close proximity of the device. If
    > + the input device may be used freely in three dimensions, consider ABS_Z
    > + instead.
    > +* ABS_MT_<name>:
    > + - Used to describe multitouch input events. Please see
    > + multi-touch-protocol.txt for details.
    > +
    > +EV_SW:
    > +----------
    > +EV_SW events describe stateful binary switches. For example, the SW_LID code is
    > +used to denote when a laptop lid is closed.
    > +
    > +EV_MSC:
    > +----------
    > +EV_MSC events are used for input and output events that do not fall under other
    > +categories.
    > +
    > +EV_LED:
    > +----------
    > +EV_LED events are used for input and output to set and query the state of
    > +various LEDs on devices.
    > +
    > +EV_REP:
    > +----------
    > +EV_REP events are used for specifying autorepeating events.
    > +
    > +EV_SND:
    > +----------
    > +EV_SND events are used for sending sound commands to simple sound output
    > +devices.
    > +
    > +EV_FF:
    > +----------
    > +EV_FF events are used to initialize a force feedback capable device and to cause
    > +such device to feedback.
    > +
    > +EV_PWR:
    > +----------
    > +EV_PWR events are a special type of key event used specifically for monitoring
    > +power buttons and switches. The two codes in use are:
    > +
    > +* KEY_POWER:
    > + - Used to denote a power button event.
    > +* KEY_SUSPEND:
    > + - Used to denote a suspend button event.
    > --
    > 1.7.1


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