This document describes how keyboard input gets translated into Android actions and how you can customize key layout and key character maps to match the needs of your own device.
Android uses the standard Linux input event device (/dev/event0) and driver as described in the linux/input.h kernel header file. For more information regarding standard Linux input drivers, please see Linux Input drivers at http://kernel.org.
Functionality
Android's input event device is structured around an interrupt or polling routine that captures the device-specific scancode and converts it to a standard form acceptable to Linux (as defined in input.h) before passing it to the kernel with input_event().
The keymap driver's other primary function is to establish a probe function that sets up the interrupt or polling function, handles hardware initialization, and attaches the driver to the input subsystem with input_register_device().
The table below describes the steps required to translate from keyboard input to application action:
| Step | Action | Explanation |
|---|---|---|
| 1. | Window manager reads key event from Linux keyboard driver. | Events are typically positional. For example, the top-left position on a keypad returns 16 regardless of whether that key is printed with a Q (as on a QWERTY keypad) or an A (as on an AZERTY keypads). This first conversion by the Linux Keyboard Driver yields a scancode (for example, 16). |
| 2. | Window manager maps scancode to keycode. | When the window manager reads a key event out of the driver, it maps the scancode to a keycode using a key layout map file. Typically, the keycode is the primary symbol screen-printed on a key. For example, KEYCODE_DPAD_CENTER is the center button on the five-way navigation control. Even though ALT + G generates a "?" character, KEYCODE_G is the keycode. |
| 3. | Window manager sends both the scancode and the keycode to the application. | Both the scancode and keycode are handled by the view with focus. How the application interprets both depend on the application. |
Key Layout Map
Selection of a Key Layout Map
Key layout maps are installed in /system/usr/keylayout and /data/usr/keylayout.
For each keyboard device xxx, set the android.keylayout.xxx system property (see Building New Device for help setting system properties). If you don't specify a keylayout file, Android will default to /system/usr/keylayout/qwerty.kl.
File Format
Key layout maps are stored on the device as UTF-8 text files and have the following characteristics:
- Comments: The pound symbol (#) denotes a comment and everything after the pound symbol on a line is ignored.
- Whitespace: All empty lines are ignored.
- Key definitions: Key definitions follow the syntax
key SCANCODE KEYCODE [FLAGS...], whereSCANCODEis a number,KEYCODEis defined in your specific keylayout file (android.keylayout.xxx), and potentialFLAGSare defined as follows:- SHIFT: While pressed, the shift key modifier is set
- ALT: While pressed, the alt key modifier is set
- CAPS: While pressed, the caps lock key modifier is set
- WAKE: When this key is pressed while the device is asleep, the device will wake up and the key event gets sent to the app.
- WAKE_DROPPED: When this key is pressed while the device is asleep, the device will wake up and the key event does not get sent to the app.
Example of a Key Layout Map File
The following code comes from android/src/device/product/generic/tuttle2.kl and is an example of a complete key layout file:
# Copyright 2007 Google Inc.
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 158 BACK WAKE_DROPPED
key 230 SOFT_RIGHT WAKE
key 60 SOFT_RIGHT WAKE
key 107 ENDCALL WAKE_DROPPED
key 62 ENDCALL WAKE_DROPPED
key 229 MENU WAKE_DROPPED
key 59 MENU WAKE_DROPPED
key 228 POUND
key 227 STAR
key 231 CALL WAKE_DROPPED
key 61 CALL WAKE_DROPPED
key 232 DPAD_CENTER WAKE_DROPPED
key 108 DPAD_DOWN WAKE_DROPPED
key 103 DPAD_UP WAKE_DROPPED
key 102 HOME WAKE
key 105 DPAD_LEFT WAKE_DROPPED
key 106 DPAD_RIGHT WAKE_DROPPED
key 115 VOLUME_UP
key 114 VOLUME_DOWN
key 116 POWER WAKE
key 212 SLASH
key 16 Q
key 17 W
key 18 E
key 19 R
key 20 T
key 21 Y
key 22 U
key 23 I
key 24 O
key 25 P
key 30 A
key 31 S
key 32 D
key 33 F
key 34 G
key 35 H
key 36 J
key 37 K
key 38 L
key 14 DEL
key 44 Z
key 45 X
key 46 C
key 47 V
key 48 B
key 49 N
key 50 M
key 51 COMMA
key 52 PERIOD
key 28 NEWLINE
key 56 ALT_LEFT
key 42 SHIFT_LEFT
key 215 AT
key 57 SPACE
key 53 SLASH
key 127 SYM
key 100 ALT_LEFT
key 399 GRAVE
Key Character Map
Selection of a Key Character Map
Key character maps are installed in /system/usr/keychars and /data/usr/keychars.
For each keyboard device xxx, set the android.keychar.xxx system property to the full path of the desired keychar file. If you don't specify a keychar file, Android will default to /system/usr/keychar/qwerty.kl.
File Format
Key character maps are stored on the device as binary resources in order to reduce loading time. Key character maps have the following characteristics:
- Comments: The pound symbol (#) denotes a comment and everything after the pound symbol on a line is ignored.
- Whitespace: All empty lines are ignored.
- Column definitions: Column definitions follow the syntax
columns MODIFIERS [...], whereMODIFIERSare defined as follows:Character in MODIFIERS Corresponding bit in the modifiers O no modifiers S MODIFIER_SHIFT C MODIFIER_CONTROL L MODIFIER_CAPS_LOCK A MODIFIER_ALT - Key definitions: Key definitions have the syntax
key SCANCODE CHARACTER [...]whereSCANCODEis a number andCHARACTERvalues are either UTF-8 characters in quotation marks (for example, "a") or a numeric value thatstrtolcan parse.
Example of a Key Character Map File
The following code comes from android/src/device/product/generic/tuttle2.kcm and represents a complete key character file:
The type line indicates what kind of keyboard your device implements. Possible types include:
- NUMERIC: A numeric (12-key) keyboard.
- Q14: A keyboard that includes all letters but multiple letters per key.
- QWERTY: A keyboard with all letters and possibly numbers. This option applies to all full keyboard configurations, such as AZERTY.
# Copyright 2007 Google Inc.
[type=QWERTY]
# keycode base caps fn caps_fn number display_label
A 'a' 'A' '%' 0x00 '%' 'A'
B 'b' 'B' '=' 0x00 '=' 'B'
C 'c' 'C' '8' 0x00E7 '8' 'C'
D 'd' 'D' '5' 0x00 '5' 'D'
E 'e' 'E' '2' 0x0301 '2' 'E'
F 'f' 'F' '6' 0x00A5 '6' 'F'
G 'g' 'G' '-' '_' '-' 'G'
H 'h' 'H' '[' '{' '[' 'H'
I 'i' 'I' '$' 0x0302 '$' 'I'
J 'j' 'J' ']' '}' ']' 'J'
K 'k' 'K' '"' '~' '"' 'K'
L 'l' 'L' ''' '`' ''' 'L'
M 'm' 'M' '>' 0x00 '>' 'M'
N 'n' 'N' '<' 0x0303 '<' 'N'
O 'o' 'O' '(' 0x00 '(' 'O'
P 'p' 'P' ')' 0x00 ')' 'P'
Q 'q' 'Q' '*' 0x0300 '*' 'Q'
R 'r' 'R' '3' 0x20AC '3' 'R'
S 's' 'S' '4' 0x00DF '4' 'S'
T 't' 'T' '+' 0x00A3 '+' 'T'
U 'u' 'U' '&' 0x0308 '&' 'U'
V 'v' 'V' '9' '^' '9' 'V'
W 'w' 'W' '1' 0x00 '1' 'W'
X 'x' 'X' '7' 0xEF00 '7' 'X'
Y 'y' 'Y' '!' 0x00A1 '!' 'Y'
Z 'z' 'Z' '#' 0x00 '#' 'Z'
COMMA ',' ';' ';' '|' ',' ','
PERIOD '.' ':' ':' 0x2026 '.' '.'
AT '@' '0' '0' 0x2022 '0' '@'
SLASH '/' '?' '?' '\' '/' '/'
SPACE 0x20 0x20 0x9 0x9 0x20 0x20
NEWLINE 0xa 0xa 0xa 0xa 0xa 0xa
# on pc keyboards
TAB 0x9 0x9 0x9 0x9 0x9 0x9
0 '0' ')' ')' ')' '0' '0'
1 '1' '!' '!' '!' '1' '1'
2 '2' '@' '@' '@' '2' '2'
3 '3' '#' '#' '#' '3' '3'
4 '4' '$' '$' '$' '4' '4'
5 '5' '%' '%' '%' '5' '5'
6 '6' '^' '^' '^' '6' '6'
7 '7' '&' '&' '&' '7' '7'
8 '8' '*' '*' '*' '8' '8'
9 '9' '(' '(' '(' '9' '9'
GRAVE '`' '~' '`' '~' '`' '`'
MINUS '-' '_' '-' '_' '-' '-'
EQUALS '=' '+' '=' '+' '=' '='
LEFT_BRACKET '[' '{' '[' '{' '[' '['
RIGHT_BRACKET ']' '}' ']' '}' ']' ']'
BACKSLASH '\' '|' '\' '|' '\' '\'
SEMICOLON ';' ':' ';' ':' ';' ';'
APOSTROPHE ''' '"' ''' '"' ''' '''
STAR '*' '*' '*' '*' '*' '*'
POUND '#' '#' '#' '#' '#' '#'
PLUS '+' '+' '+' '+' '+' '+'
Resource Binary File Format
The file snippet above gets converted to the following by the makekcharmap tool as part of the build process. You can mmap this file in and share the approximately 4k of memory that it uses between processes to minimize load time.
| Offset | Size (bytes) | Description |
|---|---|---|
| 0x00-0x0b | The ascii value "keycharmap1" including the null character | |
| 0x0c-0x0f | padding | |
| 0x10-0x13 | The number of entries in the modifiers table (COLS) | |
| 0x14-0x17 | The number of entries in the characters table (ROWS) | |
| 0x18-0x1f | padding | |
| 4*COLS | Modifiers table. The modifier mask values that each of the columns in the characters table correspond to. | |
| padding to the next 16 byte boundary | ||
| 4*COLS*ROWS | Characters table. The modifier mask values that each of the columns correspond to. |
Implementing Your Own Driver (Driver Template)
The following file, pguide_events.c, illustrates how to implement an Android keymap driver.
/* * pguide_events.c * * ANDROID PORTING GUIDE: INPUT EVENTS DRIVER TEMPLATE * * This template is designed to an example of the functionality * necessary for Android to recieve input events. The PGUIDE_EVENT * macros are meant as pointers indicating where to implement the * hardware specific code necessary for the new device. The existence * of the macros is not meant to trivialize the work required, just as * an indication of where the work needs to be done. * * Copyright 2007, Google Inc. * Based on goldfish-events.c * */ #include#include #include #include #include #include #include #include #include #define PGUIDE_EVENTS_INTERRUPT do{} while(0) #define PGUIDE_EVENTS_PROBE do{} while(0) struct event_dev { struct input_dev *input; int irq; }; static irqreturn_t pguide_events_interrupt(int irq, void *dev_id) { struct event_dev *edev = dev_id; unsigned type=0, code=0, value=0; /* Set up type, code, and value per input.h */ PGUIDE_EVENTS_INTERRUPT; input_event(edev->input, type, code, value); return IRQ_HANDLED; } static int pguide_events_probe(struct platform_device *pdev) { struct input_dev *input_dev; struct event_dev *edev; printk("*** pguide events probe ***\n"); edev = kzalloc(sizeof(struct event_dev), GFP_KERNEL); input_dev = input_allocate_device(); /* Setup edev->irq and do any hardware init */ PGUIDE_EVENTS_PROBE; if(request_irq(edev->irq, pguide_events_interrupt, 0, "pguide_events", edev) < 0) { goto fail; } /* indicate that we generate key events */ set_bit(EV_KEY, input_dev->evbit); set_bit(EV_REL, input_dev->evbit); set_bit(EV_ABS, input_dev->evbit); /* indicate that we generate *any* key event */ bitmap_fill(input_dev->keybit, KEY_MAX); bitmap_fill(input_dev->relbit, REL_MAX); bitmap_fill(input_dev->absbit, ABS_MAX); platform_set_drvdata(pdev, edev); input_dev->name = "pguide_events"; input_dev->private = edev; input_dev->cdev.dev = &pdev->dev; input_register_device(input_dev); return 0; fail: kfree(edev); input_free_device(input_dev); return -EINVAL; } static struct platform_driver pguide_events_driver = { .probe = pguide_events_probe, .driver = { .name = "pguide_events", }, }; static int __devinit pguide_events_init(void) { return platform_driver_register(&pguide_events_driver); } static void __exit pguide_events_exit(void) { } module_init(pguide_events_init); module_exit(pguide_events_exit); MODULE_DESCRIPTION("Pguide Event Device"); MODULE_LICENSE("GPL");
Sample Implementation
Assume the following for the setup of a new keypad device:
android.keylayout.partnerxx_keypad = /system/usr/keylayout/partnerxx_keypad.kl android.keychar.partnerxx_keypad = /system/usr/keychars/partnerxx.kcm
The following example log file indicates that you have correctly registered the new keypad:
I/EventHub( 1548): New device: path=/dev/input/event0 name=partnerxx_keypad id=0x10000 (of 0x1) index=1 fd=30 I/EventHub( 1548): new keyboard input device added, name = partnerxx_keypad D/WindowManager( 1548): Starting input thread. D/WindowManager( 1548): Startup complete! I/EventHub( 1548): New keyboard: name=partnerxx_keypad keymap=partnerxx_keypad.kl keymapPath=/system/usr/keychars/partnerxx_keypad.kcm.bin I/ServiceManager( 1535): ServiceManager: addService(window, 0x13610) I/EventHub( 1548): Reporting device opened: id=0x10000, name=/dev/input/event0 I/KeyInputQueue( 1548): Device added: id=0x10000, name=partnerxx_keypad, classes=1 I/KeyInputQueue( 1548): Keymap: partnerxx_keypad.kl
The snippet above contains artificial line breaks to maintain a print-friendly document.