Android 中的燈光子系統採用的是硬件訪問服務框架，JNI 層的文件是 com_android_server_lights_LightsService.cpp (frameworks\base\services\core\jni)
Java 程序通過 JNI 調用 setLight_native 來控制背光、通知燈、電池燈燈。
Java: frameworks/base/services/core/java/com/android/server/lights/LightsService.java
JNI: frameworks/base/services/core/jni/com_android_server_lights_LightsService.cpp
Hal: lights.c
默認配色：frameworks/base/core/res/res/values/config.xml
電池燈：frameworks/base/services/core/java/com/android/server/BatteryService.java
通知燈：frameworks/base/services/core/java/com/android/server/notification/NotificationManagerService.java
static light_device_t* get_device(hw_module_t* module, char const* name)
{
int err;
hw_device_t* device;
err = module->methods->open(module, name, &device);
if (err == 0) {
return (light_device_t*)device;
} else {
return NULL;
}
}
static jlong init_native(JNIEnv *env, jobject clazz)
{
int err;
hw_module_t* module;
Devices* devices;
devices = (Devices*)malloc(sizeof(Devices));
err = hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);
if (err == 0) {
devices->lights[LIGHT_INDEX_BACKLIGHT]
= get_device(module, LIGHT_ID_BACKLIGHT);
...
devices->lights[LIGHT_INDEX_BATTERY]
= get_device(module, LIGHT_ID_BATTERY);
devices->lights[LIGHT_INDEX_ATTENTION]
= get_device(module, LIGHT_ID_ATTENTION);
...
} else {
memset(devices, 0, sizeof(Devices));
}
return (jlong)devices;
}
JNI 文件通過多次調用 open 函數，獲得多個不同的 light_device_t ，存入 devices->lights 數組，通過不同的 light_device_t
調用 devices->lights[light]->set_light(devices->lights[light], &state);
static int open_lights (const struct hw_module_t* module, char const* name,
struct hw_device_t** device) {
int (*set_light)(struct light_device_t* dev,
struct light_state_t const *state);
if (0 == strcmp(LIGHT_ID_BACKLIGHT, name)) {
set_light = set_light_backlight;
}
else if (0 == strcmp(LIGHT_ID_BATTERY, name)) {
set_light = set_light_battery;
}
else if (0 == strcmp(LIGHT_ID_NOTIFICATIONS, name)) {
set_light = set_light_notifications;
}
else {
return -EINVAL;
}
pthread_once (&g_init, init_globals);
struct light_device_t *dev = malloc(sizeof (struct light_device_t));
memset(dev, 0, sizeof(*dev));
dev->common.tag = HARDWARE_DEVICE_TAG;
dev->common.version = 0;
dev->common.module = (struct hw_module_t*)module;
dev->common.close = (int (*)(struct hw_device_t*))close_lights;
dev->set_light = set_light;
*device = (struct hw_device_t*)dev;
return 0;
}
static struct hw_module_methods_t lights_module_methods = {
.open = open_lights,
};
以背光爲例：
char const*const LCD_BACKLIGHT_FILE = "/dev/backlight-1wire";
static int rgb_to_brightness (struct light_state_t const* state) {
int color = state->color & 0x00ffffff;
return ((77*((color>>16)&0x00ff))
+ (150*((color>>8)&0x00ff)) + (29*(color&0x00ff))) >> 8;
}
/* The actual lights controlling section */
static int set_light_backlight (struct light_device_t *dev, struct light_state_t const *state) {
int brightness = rgb_to_brightness(state);
ALOGV("%s brightness=%d color=0x%08x", __func__,brightness,state->color);
pthread_mutex_lock(&g_lock);
/* brightness 0-255 */
/* LCD_BACKLIGHT_FILE能接收是0-127 */
write_int (LCD_BACKLIGHT_FILE, brightness/2);
pthread_mutex_unlock(&g_lock);
return 0;
}
電池燈和通知燈使用的是同一個硬件（RGB三顆led），使用開發板上的3個普通led進行模擬
char const*const RED_LED_FILE = "/sys/class/leds/led1/brightness";
char const*const GREEN_LED_FILE = "/sys/class/leds/led2/brightness";
char const*const BLUE_LED_FILE = "/sys/class/leds/led3/brightness";
代碼不在分析
設置LED狀態：
struct light_state_t {
/**
* The color of the LED in ARGB.
*
* Do your best here.
* - If your light can only do red or green, if they ask for blue,
* you should do green.
* - If you can only do a brightness ramp, then use this formula:
* unsigned char brightness = ((77*((color>>16)&0x00ff))
* + (150*((color>>8)&0x00ff)) + (29*(color&0x00ff))) >> 8;
* - If you can only do on or off, 0 is off, anything else is on.
*
* The high byte should be ignored. Callers will set it to 0xff (which
* would correspond to 255 alpha).
*/
unsigned int color; // 把燈設爲什麼顏色, 或 把LCD的亮度設爲什麼
/**
* See the LIGHT_FLASH_* constants
*/
int flashMode; // 是否閃爍, LIGHT_FLASH_NONE表示不閃
int flashOnMS; // 亮的時間
int flashOffMS;// 滅的時間
/**
* Policy used by the framework to manage the light's brightness.
* Currently the values are BRIGHTNESS_MODE_USER and BRIGHTNESS_MODE_SENSOR.
*/
int brightnessMode; // 表示LCD的背光亮度模式
};
完整 HAL 代碼
#define LOG_NDEBUG 0
#define LOG_TAG "lights"
#include <cutils/log.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <pthread.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <hardware/lights.h>
char const*const RED_LED_FILE = "/sys/class/leds/led1/brightness";
char const*const GREEN_LED_FILE = "/sys/class/leds/led2/brightness";
char const*const BLUE_LED_FILE = "/sys/class/leds/led3/brightness";
char const*const RED_LED_FILE_TRIGGER = "/sys/class/leds/led1/trigger";
char const*const GREEN_LED_FILE_TRIGGER = "/sys/class/leds/led2/trigger";
char const*const BLUE_LED_FILE_TRIGGER = "/sys/class/leds/led3/trigger";
char const*const RED_LED_FILE_DELAYON = "/sys/class/leds/led1/delay_on";
char const*const GREEN_LED_FILE_DELAYON = "/sys/class/leds/led2/delay_on";
char const*const BLUE_LED_FILE_DELAYON = "/sys/class/leds/led3/delay_on";
char const*const RED_LED_FILE_DELAYOFF = "/sys/class/leds/led1/delay_off";
char const*const GREEN_LED_FILE_DELAYOFF = "/sys/class/leds/led2/delay_off";
char const*const BLUE_LED_FILE_DELAYOFF = "/sys/class/leds/led3/delay_off";
char const*const LCD_BACKLIGHT_FILE = "/dev/backlight-1wire";
/* Synchronization primities */
static pthread_once_t g_init = PTHREAD_ONCE_INIT;
static pthread_mutex_t g_lock = PTHREAD_MUTEX_INITIALIZER;
/* Mini-led state machine */
static struct light_state_t g_notification;
static struct light_state_t g_battery;
static int write_int (const char *path, int value) {
int fd;
static int already_warned = 0;
fd = open(path, O_RDWR);
if (fd < 0) {
if (already_warned == 0) {
ALOGE("write_int failed to open %s\n", path);
already_warned = 1;
}
return -errno;
}
char buffer[20];
int bytes = snprintf(buffer, sizeof(buffer), "%d\n", value);
int written = write (fd, buffer, bytes);
close(fd);
return written == -1 ? -errno : 0;
}
static int write_string (const char *path, const char *value) {
int fd;
static int already_warned = 0;
fd = open(path, O_RDWR);
if (fd < 0) {
if (already_warned == 0) {
ALOGE("write_string failed to open %s\n", path);
already_warned = 1;
}
return -errno;
}
char buffer[20];
int bytes = snprintf(buffer, sizeof(buffer), "%s\n", value);
int written = write (fd, buffer, bytes);
close(fd);
return written == -1 ? -errno : 0;
}
/* Color tools */
static int is_lit (struct light_state_t const* state) {
return state->color & 0x00ffffff;
}
static int rgb_to_brightness (struct light_state_t const* state) {
int color = state->color & 0x00ffffff;
return ((77*((color>>16)&0x00ff))
+ (150*((color>>8)&0x00ff)) + (29*(color&0x00ff))) >> 8;
}
/* The actual lights controlling section */
static int set_light_backlight (struct light_device_t *dev, struct light_state_t const *state) {
int brightness = rgb_to_brightness(state);
ALOGV("%s brightness=%d color=0x%08x", __func__,brightness,state->color);
pthread_mutex_lock(&g_lock);
/* brightness 0-255 */
/* LCD_BACKLIGHT_FILE能接收是0-127 */
write_int (LCD_BACKLIGHT_FILE, brightness/2);
pthread_mutex_unlock(&g_lock);
return 0;
}
static void set_shared_light_locked (struct light_device_t *dev, struct light_state_t *state) {
int r, g, b;
int delayOn,delayOff;
r = (state->color >> 16) & 0xFF;
g = (state->color >> 8) & 0xFF;
b = (state->color) & 0xFF;
delayOn = state->flashOnMS;
delayOff = state->flashOffMS;
if (state->flashMode != LIGHT_FLASH_NONE) {
write_string (RED_LED_FILE_TRIGGER, "timer");
write_string (GREEN_LED_FILE_TRIGGER, "timer");
write_string (BLUE_LED_FILE_TRIGGER, "timer");
write_int (RED_LED_FILE_DELAYON, delayOn);
write_int (GREEN_LED_FILE_DELAYON, delayOn);
write_int (BLUE_LED_FILE_DELAYON, delayOn);
write_int (RED_LED_FILE_DELAYOFF, delayOff);
write_int (GREEN_LED_FILE_DELAYOFF, delayOff);
write_int (BLUE_LED_FILE_DELAYOFF, delayOff);
} else {
write_string (RED_LED_FILE_TRIGGER, "none");
write_string (GREEN_LED_FILE_TRIGGER, "none");
write_string (BLUE_LED_FILE_TRIGGER, "none");
}
write_int (RED_LED_FILE, r);
write_int (GREEN_LED_FILE, g);
write_int (BLUE_LED_FILE, b);
}
static void handle_shared_battery_locked (struct light_device_t *dev) {
if (is_lit (&g_notification)) {
set_shared_light_locked (dev, &g_notification);
} else {
set_shared_light_locked (dev, &g_battery);
}
}
static int set_light_battery (struct light_device_t *dev, struct light_state_t const* state) {
ALOGV("%s flashMode=%d onMS = %d offMS = %d color=0x%08x", __func__,state->flashMode,state->flashOnMS,state->flashOffMS,state->color);
pthread_mutex_lock (&g_lock);
g_battery = *state;
handle_shared_battery_locked(dev);
pthread_mutex_unlock (&g_lock);
return 0;
}
static int set_light_notifications (struct light_device_t *dev, struct light_state_t const* state) {
ALOGV("%s flashMode=%d onMS = %d offMS = %d color=0x%08x", __func__,state->flashMode,state->flashOnMS,state->flashOffMS,state->color);
pthread_mutex_lock (&g_lock);
g_notification = *state;
handle_shared_battery_locked(dev);
pthread_mutex_unlock (&g_lock);
return 0;
}
/* Initializations */
void init_globals () {
pthread_mutex_init (&g_lock, NULL);
}
/* Glueing boilerplate */
static int close_lights (struct light_device_t *dev) {
if (dev)
free(dev);
return 0;
}
static int open_lights (const struct hw_module_t* module, char const* name,
struct hw_device_t** device) {
int (*set_light)(struct light_device_t* dev,
struct light_state_t const *state);
if (0 == strcmp(LIGHT_ID_BACKLIGHT, name)) {
set_light = set_light_backlight;
}
else if (0 == strcmp(LIGHT_ID_BATTERY, name)) {
set_light = set_light_battery;
}
else if (0 == strcmp(LIGHT_ID_NOTIFICATIONS, name)) {
set_light = set_light_notifications;
}
else {
return -EINVAL;
}
pthread_once (&g_init, init_globals);
struct light_device_t *dev = malloc(sizeof (struct light_device_t));
memset(dev, 0, sizeof(*dev));
dev->common.tag = HARDWARE_DEVICE_TAG;
dev->common.version = 0;
dev->common.module = (struct hw_module_t*)module;
dev->common.close = (int (*)(struct hw_device_t*))close_lights;
dev->set_light = set_light;
*device = (struct hw_device_t*)dev;
return 0;
}
static struct hw_module_methods_t lights_module_methods = {
.open = open_lights,
};
struct hw_module_t HAL_MODULE_INFO_SYM = {
.tag = HARDWARE_MODULE_TAG,
.version_major = 1,
.version_minor = 0,
.id = LIGHTS_HARDWARE_MODULE_ID,
.name = "Sony lights module",
.methods = &lights_module_methods,
};