文章一
1,总论
背光模块属于HAL层开发，HAL层开发，用一句话来概括就是定义一个hardware.h中定义的名称为宏HAL_MODULE_INFO_SYM的hw_module_t结构体，
然后实现结构体的相关内容
2,驱动方面的准备
简单的嵌入式linux驱动，编写LCD背光驱动，并提供接口给上层修改，我所用的是直接修改接口文件，接口如下：
/sys/class/backlight/pwm-backlight/brightness 这个是亮度调节
/sys/class/backlight/pwm-backlight/max_brightness 这个是最大亮度，按照android系统的要求应该设置成255
控制亮度直接写brightness文件即可
背光驱动主要是通过PWM来完成，这里不详细说明。
3,需要包含的头文件
/hardware/libhardware/include/hardware目录下的hardware.h和lights.h
其中hardware.h中定义了通用硬件模块，lights.h中定义了背光设备相关的内容
4,android已有的硬件模块在/hardware/libhardware/modules目录下，为了区分，我们开发的背光模块放置在如下的目录：
vendor/ardent/merlin/lights目录下，编译成lights.default.so放置到/system/lib/hw目录下，模块命名规则可以
参考上一节的内容。
5,修改vendor/ardent/merlin目录下AndroidBoard.mk文件，添加如下内容：
include $(LOCAL_PATH)/lights/Mdroid.mk
6,lights目录新建Mdroid.mk文件，内容如下：
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)/hw
LOCAL_SRC_FILES:= lights.c
LOCAL_SHARED_LIBRARIES := /
libutils /
libcutils /
libhardware
LOCAL_PRELINK_MODULE := false
LOCAL_MODULE := lights.default
include $(BUILD_SHARED_LIBRARY)
7,lights目录下新建一个lights.c文件，如下：
const struct hw_module_t HAL_MODULE_INFO_SYM = {
.tag = HARDWARE_MODULE_TAG,
.version_major = 1,
.version_minor = 0,
.id = LIGHTS_HARDWARE_MODULE_ID,
.name = "lights module",
.author = "allen",
.methods = NULL,
};
8，上面的内容可以直接编译通过，但是因为我将其methods部分指向了空指针，因此没有任何功能，下面来实现此部分
hw_module_t机构体的methods成员是一个指向hw_module_methods_t结构体的一个指针，hw_module_methods_t结构体定义如下：
typedef struct hw_module_methods_t {
int (*open)(const struct hw_module_t* module, const char* id,struct hw_device_t** device);
} hw_module_methods_t;
据此我们定义一个hw_module_methods_t类型的参数lights_module_methods如下：
struct hw_module_methods_t lights_module_methods = {
.open = lights_device_open
};
然后将上面的methods由NULL改成lights_module_methods
9,接下来就是定义lights_device_open函数了，此函数的参数和返回值由hw_module_methods_t结构体的open成员决定，此函数定义如下：
static int lights_device_open(const struct hw_module_t *module,const char *id, struct hw_device_t **device)
从lights_device_open函数的参数来看，第一个参数和第二个参数是常量，第三个参数是 一个指向hw_device_t结构体的指针，因此可以断定
实现此函数也就是要完成第三个参数的内容，详细的内容我们可以参考直接调用该函数的内容，在frameworks/base/services/jni目录下的
com_android_server_LightsService.cpp文件中，内容如下：
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;//device由hw_device_t指针强制转换成light_device_t指针
} else {
return NULL;
}
}
static jint 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_KEYBOARD]
= get_device(module, LIGHT_ID_KEYBOARD);
devices->lights[LIGHT_INDEX_BUTTONS]
= get_device(module, LIGHT_ID_BUTTONS);
devices->lights[LIGHT_INDEX_BATTERY]
= get_device(module, LIGHT_ID_BATTERY);
devices->lights[LIGHT_INDEX_NOTIFICATIONS]
= get_device(module, LIGHT_ID_NOTIFICATIONS);
devices->lights[LIGHT_INDEX_ATTENTION]
= get_device(module, LIGHT_ID_ATTENTION);
devices->lights[LIGHT_INDEX_BLUETOOTH]
= get_device(module, LIGHT_ID_BLUETOOTH);
devices->lights[LIGHT_INDEX_WIFI]
= get_device(module, LIGHT_ID_WIFI);
} else {
memset(devices, 0, sizeof(Devices));
}
return (jint)devices;
}
从上面的内容我们可以看出lights_device_open的第一个参数是JNI层用hw_get_module所获得，第二个参数根据设备的不同有很多种情况
该参数的内容定义在lights.h中，全部情况如下：
#define LIGHT_ID_BACKLIGHT "backlight"
#define LIGHT_ID_KEYBOARD "keyboard"
#define LIGHT_ID_BUTTONS "buttons"
#define LIGHT_ID_BATTERY "battery"
#define LIGHT_ID_NOTIFICATIONS "notifications"
#define LIGHT_ID_ATTENTION "attention"
#define LIGHT_ID_BLUETOOTH "bluetooth"
#define LIGHT_ID_WIFI "wifi"
lights调节有背光，键盘，按键，电池，通知，提醒，蓝牙和WIF
第三个参数是一个指向一个hw_device_t的指针，但是com_android_server_LightsService.cpp文件中的背光调节函数定义如下：
static void setLight_native(JNIEnv *env, jobject clazz, int ptr,
int light, int colorARGB, int flashMode, int onMS, int offMS, int brightnessMode)
{
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;
state.brightnessMode = brightnessMode;
devices->lights[light]->set_light(devices->lights[light], &state);
}
get_device函数中将hw_device_t指针强制转换成light_device_t指针给调节背光用，而light_device_t定义如下：
struct light_device_t {
struct hw_device_t common;
int (*set_light)(struct light_device_t* dev,
struct light_state_t const* state);
};
因此在实现lights_device_open的第三个参数的时候，我们应该定义一个light_device_t类型结构体，然后
将起common域的指针地址传递过去。这样虽然传递的是一个hw_device_t指针地址，但是JNI层可以将其强制转换
成light_device_t指针地址用，否则devices->lights[light]->set_light就会起不到作用了。实现如下：
static int lights_device_open(const struct hw_module_t *module,const char *id, struct hw_device_t **device)
{
struct light_device_t *dev = NULL;
int resvalue = -1;
dev = calloc(sizeof(struct light_device_t),1);
dev->common.tag = HARDWARE_DEVICE_TAG;
dev->common.version = 0;
dev->common.module = (struct hw_module_t *)module;
dev->common.close = lights_device_close;
if(!strcmp(id, LIGHT_ID_BACKLIGHT))
{
dev->set_light = lcd_set_light;
resvalue = 0;
}
else
{
dev->set_light = other_set_light;
resvalue = 0;
}
*device = &dev->common;
return resvalue;
}
10，实现lights_device_close，lcd_set_light和other_set_light，这个主要是调用驱动提供的接口直接控制硬件，举例如下：
static int lights_device_close(struct hw_device_t* device)
{
struct light_device_t *m_device = (struct light_device_t *)device;
if(m_device)
free(m_device);
return 0;
}
static int lcd_set_light(struct light_device_t* dev,struct light_state_t const* state)
{
int fd = -1;
int bytes = 0;
int rlt = -1;
unsigned char brightness = ((77*((state->color>>16)&0x00ff))
+ (150*((state->color>>8)&0x00ff))
+ (29*(state->color&0x00ff))) >> 8;
fd = open("/sys/class/backlight/pwm-backlight/brightness", O_RDWR);
if(fd>0)
{
char buffer[20];
memset(buffer, 0, 20);
bytes = sprintf(buffer, "%d", brightness);
rlt = write(fd, buffer, bytes);
if(rlt>0)
{
close(fd);
return 0;
}
}
close(fd);
return -1;
}
static int other_set_light(struct light_device_t* dev,struct light_state_t const* state)
{
return 0;
}
11，因为上面调节背光是通过写/sys/class/backlight/pwm-backlight/brightness文件来完成，因此一定要设置该文件的权限，
在init.xxx.rc文件中添加如下的内容：
# for control LCD backlight
chown system system /sys/class/backlight/pwm-backlight/brightness
chmod 0666 /sys/class/backlight/pwm-backlight/brightness
12，修改完成后经验证亮度调节可用，上面的例子只是实现了lights部分功能，如果需要完成所有的功能，请参考hardware.h, lights.h和com_android_server_LightsService.cpp文件中的内容。
文章二：
三、Android中背光系统实现
以往，我经常都是从底层往上看，这次从上层往下找找吧，同样的眼睛，不一样的视角，会别有一番风景哦~~其实，美女也要应该这样欣赏。
玩玩Android机子，其实知道背光调节就是在“设置”中的那个seekBar，那我们就去setting中去找源码吧.其源码路径为：
packages\apps\Settings\src\com\android\settings\ BrightnessPreference.java
。你会看到这样几行注释：
// Backlight range is from 0 - 255. Need to make sure that user
// doesn't set the backlight to 0 and get stuck
private static final intMINIMUM_BACKLIGHT = android.os.Power.BRIGHTNESS_DIM + 10;
private static final int MAXIMUM_BACKLIGHT = android.os.Power.BRIGHTNESS_ON;背光的调节范围是0-255啊~~
继续解带吧~会看到一个很亲切的函数：
public void UpdateBrightness()
{
if(mIsActive)
{
setBrightness(mSeekBar.getProgress() +MINIMUM_BACKLIGHT);
}
}更新背光亮度，太亲切了，这不慢慢接近目标了吗？其调用了setBrightness（）函数，跳进去看看其实现哦~~
private void setBrightness(int brightness) {
try {
IPowerManager power = IPowerManager.Stub.asInterface(
ServiceManager.getService("power"));
if (power !=null) {
power.setBacklightBrightness(brightness);
}
} catch (RemoteException doe) {
}
}这不就是韩哥给出的那几行代码嘛~~呵呵~终于找到要点了吧，所谓打蛇要打七寸，不就是这样吗？这个IPowerManager类中有个setBacklightBrightness函数啊，那它又是怎么实现的啊？找来找去只找到了一个申明啊：
public void setBacklightBrightness(int brightness)throws android.os.RemoteException;
找不到其实现怎么办呢？？这是个棘手的问题啊~还好Eclipse很恶心啊~~搜搜就又出来了，这个函数的实现在：
frameworks\base\services\java\com\android\server\PowerManagerService.java中。
1. public void setBacklightBrightness (int
2.
3. null);
4.
5. // Don't let applications turn the screen all the way off
6.
7. synchronized
8.
9. brightness = Math.max(brightness, Power.BRIGHTNESS_DIM);
10.
11. mLcdLight.setBrightness(brightness);
12.
13. //We won't adjust Button/Keyboard BKL here for the time being, see CR[ALPS00132847]
14.
15. //mKeyboardLight.setBrightness(mKeyboardVisible ? brightness : 0);
16.
17. //mButtonLight.setBrightness(brightness);
18.
19. long
20.
21. try
22.
23. mBatteryStats.noteScreenBrightness(brightness);
24.
25. catch
26.
27. "RemoteException calling noteScreenBrightness on BatteryStatsService", e);
28.
29. finally
30.
31. Binder.restoreCallingIdentity(identity);
32.
33. }
34.
35.
36.
37. // update our animation state
38.
39. synchronized
40.
41. mScreenBrightness.targetValue = brightness;
42.
43. mScreenBrightness.jumpToTargetLocked();
44.
45. }
46.
47. }
48.
49. }
看着看着又模糊啦，这里怎么又调用了setBrightness（）哦，此setBrightness非BrightnessPreference.java中的setBrightness。其类属于：
private LightsService.Light mLcdLight;
革命尚未成功，你说咋办，那好吧，为了革命的胜利，再进去看看这个类中setBrightness（）的实现吧。源码路径为：
frameworks\base\services\java\com\android\server\LightsService.java
1. public void setBrightness(int
2.
3. setBrightness(brightness, BRIGHTNESS_MODE_USER);
4.
5. }
6.
7.
8.
9. public void setBrightness(int brightness, int
10.
11. synchronized (this) {
12.
13. int color = brightness & 0x000000ff;
14.
15. 0xff000000 | (color << 16) | (color << 8) | color;
16.
17. 0, 0, brightnessMode);
18.
19. }
20.
21. }
这里又调用了setLightLocked（）
1. private void setLightLocked(int color, int mode, int onMS, int offMS, int
2.
3. if
4.
5. mColor = color;
6.
7. mMode = mode;
8.
9. mOnMS = onMS;
10.
11. mOffMS = offMS;
12.
13. setLight_native(mNativePointer, mId, color, mode, onMS, offMS, brightnessMode);
14.
15. }
16.
17. }
革命的曙光来啦，看到没，这里调用了setLight_native这个本地接口，
private static native void setLight_native(int ptr,int light,int color,int mode,
int onMS,int offMS,int brightnessMode);皇天不负有心人啊，胜利的曙光照耀着我们啊，终于就快脱光光啦~~！难以按捺住这颗激动的心啊。
可是这个setLight_native又是在哪里呢？？经过一番苦苦搜索，它并不在灯火阑珊处，而是在：
frameworks\base\services\jni\ com_android_server_LightsService.cpp
宽衣，看看：
四、JNI层
1. static void setLight_native(JNIEnv *env, jobject clazz, int
2.
3. int light, int colorARGB, int flashMode, int onMS, int offMS, int
4.
5. {
6.
7. Devices* devices = (Devices*)ptr;
8.
9. light_state_t state;
10.
11.
12.
13. if
14.
15. return
16.
17. }
18.
19.
20.
21. sizeof(light_state_t));
22.
23. state.color = colorARGB;
24.
25. state.flashMode = flashMode;
26.
27. state.flashOnMS = onMS;
28.
29. state.flashOffMS = offMS;
30.
31. state.brightnessMode = brightnessMode;
32.
33.
34.
35. devices->lights[light]->set_light(devices->lights[light], &state);
36.
37. }
38.
39.
40.
41. static
42.
43. "init_native", "()I", (void*)init_native },
44.
45. "finalize_native", "(I)V", (void*)finalize_native },
46.
47. "setLight_native", "(IIIIIII)V", (void*)setLight_native },
48.
49. };
哇，高手就是高手啊。看看，一个函数人家处理的不只是backlight，还有flash，color哦。惭愧啊~
devices->lights[light]->set_light(devices->lights[light], &state);
五、HAL层
太神奇啦，这里直接给出HAL层的源码路劲，如下：
\mediatek\source\hardware\liblights\ lights.c
\hardware\libhardware\include\hardware\ lights.h
你会看到引你越过道德边缘的set_light的申明就在lights.h中啊。真是罪孽啊~~
1. /**
2.
3. * module methods
4.
5. */
6.
7.
8.
9. /** Open a new instance of a lights device using name */
10.
11. static int open_lights(const struct hw_module_t* module, char const* name,
12.
13. struct
14.
15. {
16.
17. int (*set_light)(struct
18.
19. struct light_state_t const* state);
20.
21.
22.
23. if
24.
25. set_light = set_light_backlight;
26.
27. }
28.
29. else if
30.
31. set_light = set_light_keyboard;
32.
33. }
34.
35. else if
36.
37. set_light = set_light_buttons;
38.
39. }
40.
41. else if
42.
43. set_light = set_light_battery;
44.
45. }
46.
47. else if
48.
49. set_light = set_light_notifications;
50.
51. }
52.
53. else if
54.
55. set_light = set_light_attention;
56.
57. }
58.
59. else
60.
61. return
62.
63. }
64.
65.
66.
67. pthread_once(&g_init, init_globals);
68.
69.
70.
71. struct light_device_t *dev = malloc(sizeof(struct
72.
73. sizeof(*dev));
74.
75.
76.
77. dev->common.tag = HARDWARE_DEVICE_TAG;
78.
79. dev->common.version = 0;
80.
81. struct
82.
83. int (*)(struct
84.
85. dev->set_light = set_light;
86.
87.
88.
89. struct
90.
91. return
92.
93. }
看看吧，其实我们需要找的就是set_light_backlight。
1. static int
2.
3. set_light_backlight(struct light_device_t* dev,
4.
5. struct light_state_t const* state)
6.
7. {
8.
9. err = 0;
10.
11. brightness = rgb_to_brightness(state);
12.
13. pthread_mutex_lock(&g_lock);
14.
15. brightness=%d start+++\n", __func__, brightness);
16.
17. g_backlight = brightness;
18.
19. err = write_int(LCD_FILE, brightness);
20.
21. if (g_haveTrackballLight) {
22.
23. handle_trackball_light_locked(dev);
24.
25. }
26.
27. pthread_mutex_unlock(&g_lock);
28.
29. return err;
30.
31. }
通过这个分析，可以延伸了解到led灯的结构。
