Re: [PATCH 2/4] Documentation: Add evdev type and code definitions

[Henrik Rydberg]

Hi Chase,

this is very nice, thanks for doing this! Comments inline.

On 12/14/2010 10:21 PM, Chase Douglas wrote:

> This commit adds the file Documentation/input/evdev-codes.txt.
> 
> Signed-off-by: Chase Douglas <chase.douglas@xxxxxxxxxxxxx>
> ---
>  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.


On a general note, the transfer is stateful. It is assumed that the receiver
knows that prior state of an axes when the new value comes in. Only changed
values are emitted.

Most of the input state can be retrieved via ioctl/sysfs calls.

> +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.


We have not using the name @frame@ much so far, but i think it is a good name
for it.

> +* 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.
> +
> +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 always required, and on top of that, one or several other BTN_TOOL
can be used. There is also a quirk in that BTN_TOUCH should come first in the
event stream, for the benefit of the mousedev emulation driver.

> +
> +* 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.


In the input-mt interface, there is a function to report these,
input_mt_report_finger_count().

> +
> +* 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.
> +
> +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.
> +* 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.


The word "hovering" is commonly used to describe this usage. Many pen tablets
use it, and touch versions are emerging.

> +* 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.


Thanks,
Henrik
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