Android中背光系统架构

Mg Android中背光系统架构
Email:wei7758@126.com
Blog：http://blog.csdn.net/yinwei520
Author：Yww
Time：2011-9-24
Update:
(转载请注明出处，谢谢)
不知不觉喜欢上了写Blog,这还是一种不错的休闲方式，所噶~~，会不会也害怕过周末呢？因为寂寞~~啥样儿的生活才让觉得舒适哦~单身好~哈哈。搞了两天，还是姚哥一语惊醒梦中人啊~忽略了Linux下的权限问题，让我纠结了好几个小时啊。首先说明一下，这次学习中让我学到的东西：
最主要的莫过于是了解了Android中jni编程，游荡整个Android源码，可以看到很多直接操作底层驱动接口，封装成so库，供Java调用的例子哦。

这次学习，也正是出于这样的想法，没想到这个设想高手们早就实现了哦，菜鸟现在也只能算是验证了。诶，菜鸟就是菜鸟，有虫子吃，就兴奋的不得了。

驱动架构略，这里只讨论jni接口的实现。

一、我的设想

其实设想很简单，找到背光驱动提供给上层的API接口，人家Android还不是一样需要一层一层的抽象（HAL、Framework），高手们考虑的东东很多，所以才一层层抽象封装，既然这样，咱菜鸟不就一根筋，有虫吃就是王道啊，我为什么不能直接将这个驱动接口封装成jni提供给Java呢？其实这想法很早就有了，只是到现在才验证，确实可以啊。其实Android中还是有N多这样的例子的。

背光驱动提供的接口是：/sys/class/leds/lcd-backlight/brightness。至于这个接口是怎么来的？？那就要去看驱动结构了。驱动注册此接口的源码位于：

Kernel/driver/leds/led-class.c中。

这个文件只是实现了提供上层的接口，至于真正操作硬件的驱动程序，可以给出其源码路径为：（硬件操作其实就是脉宽调制（PWM）），mediatek\source\kernel\drivers\leds

二、设想验证

这里关键就是要清楚jni的接口实现规则咯，不过环境搭建也比较麻烦（ndk编译环境）。

环境搭建另外给出日志。

Jni接口的源码如下：

#include <unistd.h>

#include <stdio.h>

#include <stdlib.h>

#include <fcntl.h>

#include <sys/types.h>

#include <sys/stat.h>

//#include <dirent.h>

//#include <jni.h>

#include <string.h>

#include <android/log.h>

#include "com_yecon_CtlBL_CtlBLActivity.h"

#define  LOG_TAG    "ctlbl.c"

#define  LOGI(...)  __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)

//#define DEV_PATH "/sys/class/leds/lcd-backlight/brightness"

//#define DEV_PATH "/sys/devices/platform/leds-mt65xx/leds/lcd-backlight/brightness"

/**

* native method

*/

//JNIEXPORT jobjectArray JNICALL Java_com_yecon_CtlBL_CtlBLActivity_ctlbl(JNIEnv * env, jobject obj)

JNIEXPORT jint JNICALL Java_com_yecon_CtlBL_CtlBLActivity_ctlbl(JNIEnv * env, jobject obj)

{

int fd;

int err;

char *p;

char ctl[10]={"20"};

LOGI("HELLO!\n");

//__android_log_print("");

//printf("call ctlbl function succ!\n");

fd = open("/sys/class/leds/lcd-backlight/brightness",O_RDWR);

if(fd < 0)

{

//fprintf(stderr,"error: open %s\n",DEV_PATH);

LOGI("error: open!\n");

exit(1);

}

#if 0

err = read(fd,ctl,1);

if(err != 1)

{

//fprintf(stderr,"error: write %d!\n",err);

exit(1);

}else{

//printf("the data is %s\n",ctl[0]);

}

#endif

err=write(fd,ctl,2);

//printf("%s\n",ctl);

if(err != 2)

{

//fprintf(stderr,"error: write %d!\n",err);

LOGI("error: write !\n");

exit(1);

}

close(fd);

return 0;

//return (*env)->NewStringUTF(env, "Hello ww JNI !");

}

上层Java调用的源码如下：（只是实现了一个Button，点击，有一个消息响应，将背光调到20）

package com.yecon.CtlBL;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.TextView;

//import com.yecon.CtlBL.ctlbljni;

public class CtlBLActivity extends Activity {

Button b  = null;

//    ctl = new ctlbljni();

private OnClickListener clickListener = new OnClickListener(){

@Override

public void onClick(View v) {

// TODO Auto-generated method stub

//           ctl.ctlbl();

ctlbl();

}

};

/** Called when the activity is first created. */

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

b = (Button) this.findViewById(R.id.BtnCancel);

b.setOnClickListener(clickListener);

//        TextView  tv = new TextView(this);

//       tv.setText( ctlbl() );

//       setContentView(tv);

}

public native int ctlbl();//本地方法

static {

System.loadLibrary("ctlbl");//载入so库

}

}

看上去，没几行代码，so easy！！看看高手们的实现吧！！

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

打开看看吧~宽衣解带是最让人兴奋的啊。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。

public void setBacklightBrightness (int brightness) {

mContext.enforceCallingOrSelfPermission(android.Manifest.permission.DEVICE_POWER, null);

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

synchronized (mLocks) {

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

mLcdLight.setBrightness(brightness);

//We won't adjust Button/Keyboard BKL here for the time being, see CR[ALPS00132847]

//mKeyboardLight.setBrightness(mKeyboardVisible ? brightness : 0);

//mButtonLight.setBrightness(brightness);

long identity = Binder.clearCallingIdentity();

try {

mBatteryStats.noteScreenBrightness(brightness);

} catch (RemoteException e) {

Slog.w(TAG, "RemoteException calling noteScreenBrightness on BatteryStatsService", e);

} finally {

Binder.restoreCallingIdentity(identity);

}

// update our animation state

synchronized (mLocks) {

mScreenBrightness.targetValue = brightness;

mScreenBrightness.jumpToTargetLocked();

}

}

}

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

public void setBrightness(int brightness) {

setBrightness(brightness, BRIGHTNESS_MODE_USER);

}

public void setBrightness(int brightness, int brightnessMode) {

synchronized (this) {

int color = brightness & 0x000000ff;

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

setLightLocked(color, LIGHT_FLASH_NONE, 0, 0, brightnessMode);

}

}

这里又调用了setLightLocked（）

private void setLightLocked(int color, int mode, int onMS, int offMS, int brightnessMode) {

if (color != mColor || mode != mMode || onMS != mOnMS || offMS != mOffMS) {

mColor = color;

mMode = mode;

mOnMS = onMS;

mOffMS = offMS;

setLight_native(mNativePointer, mId, color, mode, onMS, offMS, brightnessMode);

}

}

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

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);

}

static JNINativeMethod method_table[] = {

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

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

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

};

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~

到此，一个美女就这样被你看完啦~~当然，还有三点哦~~还想要激情的吗？？激情就在底层了哦。想单刀直入吗？那还得看你本事了哦~~

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

这句将带你穿梭进赤裸裸的XX。

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~~

/**

* module methods

*/

/** Open a new instance of a lights device using name */

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_KEYBOARD, name)) {

set_light = set_light_keyboard;

}

else if (0 == strcmp(LIGHT_ID_BUTTONS, name)) {

set_light = set_light_buttons;

}

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 if (0 == strcmp(LIGHT_ID_ATTENTION, name)) {

set_light = set_light_attention;

}

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;

}

看看吧，其实我们需要找的就是set_light_backlight。

static int

set_light_backlight(struct light_device_t* dev,

struct light_state_t const* state)

{

int err = 0;

int brightness = rgb_to_brightness(state);

pthread_mutex_lock(&g_lock);

LOGD("%s: brightness=%d start+++\n", __func__, brightness);

g_backlight = brightness;

err = write_int(LCD_FILE, brightness);

if (g_haveTrackballLight) {

handle_trackball_light_locked(dev);

}

pthread_mutex_unlock(&g_lock);

return err;

}

当你认真看完lights.c会发现其基本思想跟之前的设想一样，只是人家是高手，我是菜鸟，人家看到赤裸裸的美女不是表面，而是艺术~~~~！！

通过这个分析，可以延伸了解到led灯的结构。