Key Layout Files from http://source.android.com
2014-08-25 21:58
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Key Layout Files
Key layout files (.klfiles) are responsible for mapping Linux key codes and axis codes to Android key codes and axis codes and specifying associated policy flags.
Device-specific key layout files are required for all internal (built-in) input devices that have keys, including special keys such as volume, power and headset media keys.
Device-specific key layout files are optional for other input devices but they are recommended for special-purpose keyboards and joysticks.
If no device-specific key layout file is available, then the system will choose a default instead.
Location
Key layout files are located by USB vendor, product (and optionally version) id or by input device name.The following paths are consulted in order.
/system/usr/keylayout/Vendor_XXXX_Product_XXXX_Version_XXXX.kl
/system/usr/keylayout/Vendor_XXXX_Product_XXXX.kl
/system/usr/keylayout/DEVICE_NAME.kl
/data/system/devices/keylayout/Vendor_XXXX_Product_XXXX_Version_XXXX.kl
/data/system/devices/keylayout/Vendor_XXXX_Product_XXXX.kl
/data/system/devices/keylayout/DEVICE_NAME.kl
/system/usr/keylayout/Generic.kl
/data/system/devices/keylayout/Generic.kl
When constructing a file path that contains the device name, all characters in the device name other than '0'-'9', 'a'-'z', 'A'-'Z', '-' or '' are replaced by ''.
Generic Key Layout File
The system provides a special built-in generic key layout file called Generic.kl. This key layout is intended to support a variety of standard external keyboards and joysticks.
Do not modify the generic key layout!
Syntax
A key layout file is a plain text file consisting of key or axis declarations and flags.
Key Declarations
Key declarations each consist of the keyword keyfollowed by a Linux key code number and an Android key code name, or the keyword `usage` followed by a HID usage and an Android key code
name. The HID usage is represented as a 32-bit integer, where the high 16-bits represent the HID usage page and the low 16-bits represent the HID usage ID. Either of these declarations can then be followed by an optional set of whitespace delimited policy
flags.
key 1 ESCAPE key 114 VOLUME_DOWN WAKE key 16 Q VIRTUAL WAKE key usage 0x0c006F BRIGHTNESS_UP
The following policy flags are recognized:
WAKE: The key should wake the device when it is asleep. For historical reasons, this flag behaves in the same manner as
WAKE_DROPPEDbelow.
WAKE_DROPPED: The key should wake the device when it is asleep but the key itself should be dropped when the wake-up occurs. In a sense, the key's action
was to wake the device, but the key itself is not processed.
SHIFT: The key should be interpreted as if the SHIFT key were also pressed.
CAPS_LOCK: The key should be interpreted as if the CAPS LOCK key were also pressed.
ALT: The key should be interpreted as if the ALT key were also pressed.
ALT_GR: The key should be interpreted as if the RIGHT ALT key were also pressed.
FUNCTION: The key should be interpreted as if the FUNCTION key were also pressed.
VIRTUAL: The key is a virtual soft key (capacitive button) that is adjacent to the main touch screen. This causes special debouncing logic to be enabled,
see below.
MENU: Deprecated. Do not use.
LAUNCHER: Deprecated. Do not use.
Axis Declarations
Axis declarations each consist of the keyword axisfollowed by a Linux axis code number, and qualifiers that control the behavior of the axis including at least one Android axis code
name.
Basic Axes
A basic axis simply maps a Linux axis code to an Android axis code name.The following declaration maps
ABS_X(indicated by
0x00) to
AXIS_X(indicated
by
X).
axis 0x00 X
In the above example, if the value of
ABS_Xis
5then
AXIS_Xwill
be set to
5.
Split Axes
A split axis maps a Linux axis code to two Android axis code names, such that values less than or greater than a threshold are split across two different axes when mapped. This mapping is useful when a single physical axis reported by the device encodes twodifferent mutually exclusive logical axes.
The following declaration maps values of the
ABS_Yaxis (indicated by
0x01) to
AXIS_GASwhen
less than
0x7for to
AXIS_BRAKEwhen greater than
0x7f.
axis 0x01 split 0x7f GAS BRAKE
In the above example, if the value of
ABS_Yis
0x7dthen
AXIS_GASis
set to
2(
0x7f - 0x7d) and
AXIS_BRAKEis
set to
0. Conversely, if the value of
ABS_Yis
0x83then
AXIS_GASis
set to
0and
AXIS_BRAKEis set to
4(
0x83 - 0x7f). Finally, if the value of
ABS_Yequals the split value of
0x7fthen both
AXIS_GASand
AXIS_BRAKEare
set to
0.
Inverted Axes
An inverted axis inverts the sign of the axis value.The following declaration maps
ABS_RZ(indicated by
0x05) to
AXIS_BRAKE(indicated
by
BRAKE), and inverts the output by negating it.
axis 0x05 invert BRAKE
In the above example, if the value of
ABS_RZis
2then
AXIS_BRAKEis
set to
-2.
Center Flat Position Option
The Linux input protocol provides a way for input device drivers to specify the center flat position of joystick axes but not all of them do and some of them provide incorrect values.The center flat position is the neutral position of the axis, such as when a directional pad is in the very middle of its range and the user is not touching it.
To resolve this issue, an axis declaration may be followed by a
flatoption that specifies the value of the center flat position for the axis.
axis 0x03 Z flat 4096
In the above example, the center flat position is set to
4096.
Comments
Comment lines begin with '#' and continue to the end of the line. Like this:# A comment!
Blank lines are ignored.
Examples
Keyboard
# This is an example of a key layout file for a keyboard. key 1 ESCAPE key 2 1 key 3 2 key 4 3 key 5 4 key 6 5 key 7 6 key 8 7 key 9 8 key 10 9 key 11 0 key 12 MINUS key 13 EQUALS key 14 DEL # etc...
System Controls
# This is an example of a key layout file for basic system controls, such as # volume and power keys which are typically implemented as GPIO pins that # the device decodes into key presses. key 114 VOLUME_DOWN WAKE key 115 VOLUME_UP WAKE key 116 POWER WAKE
Capacitive Buttons
# This is an example of a key layout file for a touch device with capacitive buttons. key 139 MENU VIRTUAL key 102 HOME VIRTUAL key 158 BACK VIRTUAL key 217 SEARCH VIRTUAL
Headset Jack Media Controls
# This is an example of a key layout file for headset mounted media controls. # A typical headset jack interface might have special control wires or detect known # resistive loads as corresponding to media functions or volume controls. # This file assumes that the driver decodes these signals and reports media # controls as key presses. key 163 MEDIA_NEXT WAKE key 165 MEDIA_PREVIOUS WAKE key 226 HEADSETHOOK WAKE
Joystick
# This is an example of a key layout file for a joystick.
# These are the buttons that the joystick supports, represented as keys.
key 304 BUTTON_A
key 305 BUTTON_B
key 307 BUTTON_X
key 308 BUTTON_Y
key 310 BUTTON_L1
key 311 BUTTON_R1
key 314 BUTTON_SELECT
key 315 BUTTON_START
key 316 BUTTON_MODE
key 317 BUTTON_THUMBL
key 318 BUTTON_THUMBR
# Left and right stick.
# The reported value for flat is 128 out of a range from -32767 to 32768, which is absurd.
# This confuses applications that rely on the flat value because the joystick actually
# settles in a flat range of +/- 4096 or so. We override it here.
axis 0x00 X flat 4096
axis 0x01 Y flat 4096
axis 0x03 Z flat 4096axis 0x04 RZ flat 4096
# Triggers.
axis 0x02 LTRIGGER
axis 0x05 RTRIGGER
# Hat.
axis 0x10 HAT_X
axis 0x11 HAT_Y
Wake Keys
Wake keys are special keys that wake the device from sleep, such as the power key.By default, for internal keyboard devices, no key is a wake key. For external keyboard device, all keys are wake keys.
To make a key be a wake key, set the
WAKE_DROPPEDflag in the key layout file for the keyboard device.
Note that the
WindowManagerPolicycomponent is responsible for implementing wake key behavior. Moreover, the key guard may prevent certain keys from functioning as wake keys. A good place
to start understanding wake key behavior is
PhoneWindowManager.interceptKeyBeforeQueueing.
Virtual Soft Keys
The input system provides special features for implementing virtual soft keys.There are three cases:
If the virtual soft keys are displayed graphically on the screen, as on the Galaxy Nexus, then they are implemented by the Navigation Bar component in the System UI package.
Because graphical virtual soft keys are implemented at a high layer in the system, key layout files are not involved and the following information does not apply.
If the virtual soft keys are implemented as an extended touchable region that is part of the main touch screen, as on the Nexus One, then the input system uses a virtual key map file to translate X / Y touch coordinates
into Linux key codes, then uses the key layout file to translate Linux key codes into Android key codes.
Refer to the section on Touch Devices for more details about virtual
key map files.
The key layout file for the touch screen input device must specify the appropriate key mapping and include the
VIRTUALflag for each key.
If the virtual soft keys are implemented as capacitive buttons that are separate from the main touch screen, as on the Nexus S, then the kernel device driver or firmware is responsible for translating touches into
Linux key codes which the input system then translates into Android key codes using the key layout file.
The key layout file for the capacitive button input device must specify the appropriate key mapping and include the
VIRTUALflag for each
key.
When virtual soft key are located within or in close physical proximity of the touch screen, it is easy for the user to accidentally press one of the buttons when touching near the bottom of the screen or when sliding a finger from top to bottom or from bottom
to top on the screen.
To prevent this from happening, the input system applies a little debouncing such that virtual soft key presses are ignored for a brief period of time after the most recent touch on the touch screen. The delay is called the virtual key quiet time.
To enable virtual soft key debouncing, we must do two things.
First, we provide a key layout file for the touch screen or capacitive button input device with the
VIRTUALflag set for each key.
key 139 MENU VIRTUAL key 102 HOME VIRTUAL key 158 BACK VIRTUAL key 217 SEARCH VIRTUAL
Then, we set the value of the virtual key quiet time in a resource overlay for the framework
config.xmlresource.
<!-- Specifies the amount of time to disable virtual keys after the screen is touched in order to filter out accidental virtual key presses due to swiping gestures or taps near the edge of the display. May be 0 to disable the feature. It is recommended that this value be no more than 250 ms. This feature should be disabled for most devices. --> <integer name="config_virtualKeyQuietTimeMillis">250</integer>
Validation
Make sure to validate your key layout files using the Validate Keymaps tool.From: https://source.android.com/devices/tech/input/key-layout-files.html
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