Android Platform Development Kit

Introduction

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...], where SCANCODE is a number, KEYCODE is defined in your specific keylayout file (android.keylayout.xxx), and potential FLAGS are 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 The Android Open Source Project

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    ENTER 
        
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 [...], where MODIFIERS are 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 [...] where SCANCODE is a number and CHARACTER values are either UTF-8 characters in quotation marks (for example, "a") or a numeric value that strtol can 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 The Android Open Source Project

[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, The Android Open Source Project
 * 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.

v0.3 - 9 June 2008