Android 背光的控制：

屏幕背光设置

packages/apps/Settings/src/com/android/settings/BrightnessPreference.java

背光设置滚动条和关闭按钮都会调用 setBrightness(mOldBrightness);

public void onProgressChanged(SeekBar seekBar, int progress,boolean fromTouch)

protected void onDialogClosed(boolean positiveResult)

private void setBrightness(int brightness) {

try {

IHardwareService hardware = IHardwareService.Stub.asInterface(

ServiceManager.getService("hardware"));

if (hardware != null) {

hardware.setBacklights(brightness);

}

} catch (RemoteException doe) {

}

}

调用硬件服务器 HardwareService 的 setBacklights 函数

HardwareService.java (frameworks\base\services\java\com\android\server):

public void setBacklights(int brightness)

{

. . .

// Don't let applications turn the screen all the way off

brightness = Math.max(brightness, Power.BRIGHTNESS_DIM);

setLightBrightness_UNCHECKED(LIGHT_ID_BACKLIGHT, brightness);

setLightBrightness_UNCHECKED(LIGHT_ID_KEYBOARD, brightness);

setLightBrightness_UNCHECKED(LIGHT_ID_BUTTONS, brightness);

. . .

}

void setLightOff_UNCHECKED(int light)

{

//本地调用 setLight_native

setLight_native(mNativePointer, light, 0, LIGHT_FLASH_NONE, 0, 0);

}

void setLightBrightness_UNCHECKED(int light, int brightness) {

int b = brightness & 0x000000ff;

b = 0xff000000 | (b << 16) | (b << 8) | b;

setLight_native(mNativePointer, light, b, LIGHT_FLASH_NONE, 0, 0);

}

因为有：

com_android_server_HardwareService.cpp (frameworks\base\services\jni):

static JNINativeMethod method_table[] = {

{ "init_native", "()I", (void*)init_native },

{ "finalize_native", "(I)V", (void*)init_native },

{ "setLight_native", "(IIIIII)V", (void*)setLight_native },

{ "vibratorOn", "(J)V", (void*)vibratorOn },

{ "vibratorOff", "()V", (void*)vibratorOff }

};

所以最终调用的是文件：

com_android_server_HardwareService.cpp (frameworks\base\services\jni)中的函数：

static void setLight_native(JNIEnv *env, jobject clazz, int ptr,

int light, int colorARGB, int flashMode, int onMS, int offMS)

{

Devices* devices = (Devices*)ptr;

light_state_t state;

if (light < 0 || light >= LIGHT_COUNT || devices->lights[light] == NULL) {

return ;

}

memset(&state, 0, sizeof(light_state_t));

state.color = colorARGB;

state.flashMode = flashMode;

state.flashOnMS = onMS;

state.flashOffMS = offMS;

devices->lights[light]->set_light(devices->lights[light], &state);

}

Lights.h (hardware\libhardware\include\hardware):#define LIGHTS_HARDWARE_MODULE_ID "lights"

com_android_server_HardwareService.cpp (frameworks\base\services\jni)

err = hw_get_module(LIGHTS_HARDWARE_MODULE_ID, (hw_module_t const**)&module);

static const char *variant_keys[] = {

"ro.hardware", /* This goes first so that it can pick up a different

file on the emulator. */

"ro.product.board",

"ro.board.platform",

"ro.arch"

};

int hw_get_module(const char *id, const struct hw_module_t **module)

status = load(id, prop, &hmi);

status = load(id, HAL_DEFAULT_VARIANT, &hmi);

static int load(const char *id, const char *variant,const struct hw_module_t **pHmi)

snprintf(path, sizeof(path), "%s/%s.%s.so", HAL_LIBRARY_PATH, id, variant);

#define HAL_DEFAULT_VARIANT "default"

#define HAL_LIBRARY_PATH "/system/lib/hw"

所以path等于：

/system/lib/hw/light.marvell.so

/system/lib/hw/light.default.so

我们编译的light模块放在 /system/lib/hw/light.default.so 所以初始化成功。

property_get(variant_keys[i], prop, NULL) 只有 ro.hardware 存在 [ro.hardware]: [marvell]

static int lights_device_open(const struct hw_module_t* module, const char* name,struct hw_device_t** device)

dev->set_light = set_light_backlight;

static struct hw_module_methods_t lights_module_methods = {

open: lights_device_open

};

hardware/libhardware/modules/lights/Android.mk

LOCAL_MODULE:= lights.default

err = module->methods->open(module, name, &device);

执行的是 ： lights_device_open

const char * const brightness_file = "/sys/class/backlight/micco-bl/brightness";

static int set_light_backlight(struct light_device_t* dev,

struct light_state_t const* state)

｛

. . .

color = state->color;

tmp = ((77*((color>>16)&0x00ff)) + (150*((color>>8)&0x00ff)) + (29*(color&0x00ff))) >> 8;

brightness = tmp/16;

LOGD("---->calling %s(),line=%d state->color=%d,brightness=%d\n",__FUNCTION__,__LINE__,state->color,brightness);

len = sprintf(buf,"%d",brightness);

len = write(fd, buf, len);

. . .

｝

上面的函数完成了与内核的交互

综上所述，程序调用流程如下，上层应用通过 /sys/class/leds/lcd-backlight/brightnes 于内核打交道

设置模块 -> 硬件服务器 -> 本地调用 ->功能库 -> 读写 /sys/class/leds/lcd-backlight/brightness 函数与内核交互

Init.rc (vendor\marvell\littleton): chown system system /sys/class/leds/keyboard-backlight/brightness

Init.rc (vendor\marvell\littleton): chown system system /sys/class/leds/lcd-backlight/brightness

Init.rc (vendor\marvell\littleton): chown system system /sys/class/leds/button-backlight/brightness

这个是博客中记录的，非常详细，很具有参考价值。

在 Atmel 开发板的背光问题解决中使用了 另外一个路径：

# pwd

/sys/class/backlight

# ls -l

lrwxrwxrwx root root 1970-01-01 00:00 backlight -> ../../devices/platform/atmel_lcdfb.0/backlight/backlight

改变该路径的属性： 可读可写。 init.rc

MK 文件

LOCAL_PATH:= $(call my-dir)

# HAL module implemenation, not prelinked and stored in

# hw/..so

include $(CLEAR_VARS)

LOCAL_SRC_FILES := lights.c

LOCAL_PRELINK_MODULE := false

LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw

LOCAL_SHARED_LIBRARIES := liblog

LOCAL_MODULE := lights.atmel

include $(BUILD_SHARED_LIBRARY)

改变 lights.c 文件中的路径。

# ls -l /system/lib/hw

-rwxrwxrwx root root 9560 2010-07-06 10:21 lights.default.so

-rwxrwxrwx root root 14040 2010-07-06 09:03 gralloc.default.so

-rwxrwxrwx root root 9560 2010-07-06 09:03 light.atmel.so.bak

-rwxrwxrwx root root 9752 2010-07-06 10:21 alsa.default.so

-rwxrwxrwx root root 9848 2010-07-06 09:03 sensors.goldfish.so

-rwxrwxrwx root root 5308 2010-07-06 10:21 acoustics.default.so

lights.default.so light.atmel.so 均可实现亮度控制。

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