Android中 LED 系统架构

Android中背光系统架构

分类： Adroid开发 Linux操作系统 嵌入式Linux驱动 2011-09-24 16:00 1650人阅读 评论(6) 收藏 举报

android struct frameworks jni notifications module

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。