本文深入解析了Android系统中灯光控制的实现原理和技术细节，包括背光、通知灯和电池灯等不同类型的灯光如何通过硬件访问服务框架进行控制。介绍了从Java层到JNI层再到HAL层的具体实现过程。
Android 中的灯光子系统采用的是硬件访问服务框架，JNI 层的文件是 com_android_server_lights_LightsService.cpp (frameworks\base\services\core\jni)
Java 程序通过 JNI 调用 setLight_native 来控制背光、通知灯、电池灯灯。
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
默认配色：frameworks/base/core/res/res/values/config.xml
电池灯：frameworks/base/services/core/java/com/android/server/BatteryService.java
通知灯：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 文件通过多次调用 open 函数，获得多个不同的 light_device_t ，存入 devices->lights 数组，通过不同的 light_device_t
调用 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,
};
以背光为例：
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;
}
电池灯和通知灯使用的是同一个硬件（RGB三颗led），使用开发板上的3个普通led进行模拟
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";
代码不在分析
设置LED状态：
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; // 把灯设为什么颜色, 或 把LCD的亮度设为什么
/**
* See the LIGHT_FLASH_* constants
*/
int flashMode; // 是否闪烁, LIGHT_FLASH_NONE表示不闪
int flashOnMS; // 亮的时间
int flashOffMS;// 灭的时间
/**
* 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 代码
#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",
.author = "Diogo Ferreira <defer@cyanogenmod.com>, Andreas Makris <Andreas.Makris@gmail.com>",
.methods = &lights_module_methods,
};
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