Android中背光系統架構

Mg Android中背光系統架構

Email:wei7758@126.com

Blog：http://blog.csdn.net/yinwei520

Author：Yww

Time：2011-9-24

Update:

(轉載請註明出處，謝謝)

         不知不覺喜歡上了寫Blog,這還是一種不錯的休閑方式，所噶~~，會不會也害怕過周末呢？因為寂寞~~啥樣兒的生活才讓覺得舒適哦~單身好~哈哈。搞了兩天，還是姚哥一語驚醒夢中人啊~忽略了Linux下的許可權問題，讓我糾結了好幾個小時啊。首先說明一下，這次學習中讓我學到的東西：

         最主要的莫過於是瞭解了Android中jni編程，遊盪整個Android源碼，可以看到很多直接操作底層驅動介面，封裝成so庫，供Java調用的例子哦。

這次學習，也正是出於這樣的想法，沒想到這個設想高手們早就實現了哦，菜鳥現在也只能算是驗證了。誒，菜鳥就是菜鳥，有蟲子吃，就興奮的不得了。

驅動架構略，這裡只討論jni介面的實現。

 

一、我的設想

    其實設想很簡單，找到背光碟機動提供給上層的API介面，人家Android還不是一樣需要一層一層的抽象（HAL、Framework），高手們考慮的東東很多，所以才一層層抽象封裝，既然這樣，咱菜鳥不就一根筋，有蟲吃就是王道啊，我為什麼不能直接將這個驅動介面封裝成jni提供給Java呢？其實這想法很早就有了，只是到現在才驗證，確實可以啊。其實Android中還是有N多這樣的例子的。

 

    背光碟機動提供的介面是：/sys/class/leds/lcd-backlight/brightness。至於這個介面是怎麼來的？？那就要去看驅動結構了。驅動註冊此介面的源碼位於：

Kernel/driver/leds/led-class.c中。

這個檔案只是實現了提供上層的介面，至於真正操作硬體的驅動程式，可以給出其源碼路徑為：（硬體操作其實就是脈寬調製（PWM）），mediatek\source\kernel\drivers\leds

 

二、設想驗證

    這裡關鍵就是要清楚jni的介面實現規則咯，不過環境搭建也比較麻煩（ndk編譯環境）。

環境搭建另外給出日誌。

Jni介面的源碼如下：

 

#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 !");    }

上層Java調用的源碼如下：（只是實現了一個Button，點擊，有一個訊息響應，將背光調到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");//載入so庫    }}

 

看上去，沒幾行代碼，so easy！！看看高手們的實現吧！！

 

三、Android中背光系統實現

以往，我經常都是從底層往上看，這次從上層往下找找吧，同樣的眼睛，不一樣的視角，會別有一番風景哦~~其實，美女也要應該這樣欣賞。

玩玩Android機子，其實知道背光調節就是在“設定”中的那個seekBar，那我們就去setting中去找源碼吧.其源碼路徑為：

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

開啟看看吧~寬衣解帶是最讓人興奮的啊。你會看到這樣幾行注釋：   

    // 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;

背光的調節範圍是0-255啊~~

繼續解帶吧~會看到一個很親切的函數：

public void UpdateBrightness()

    {

    if(mIsActive)

    {

        setBrightness(mSeekBar.getProgress() +MINIMUM_BACKLIGHT);

    }

    }

更新背光亮度，太親切了，這不慢慢接近目標了嗎？其調用了setBrightness（）函數，跳進去看看其實現哦~~

private void setBrightness(int brightness) {

        try {

            IPowerManager power = IPowerManager.Stub.asInterface(

                    ServiceManager.getService("power"));

            if (power !=null) {

                power.setBacklightBrightness(brightness);

            }

        } catch (RemoteException doe) {

           

        }       

    }

這不就是韓哥給出的那幾行代碼嘛~~呵呵~終於找到要點了吧，所謂打蛇要打七寸，不就是這樣嗎？這個IPowerManager類中有個setBacklightBrightness函數啊，那它又是怎麼實現的啊？找來找去只找到了一個申明啊：

public void setBacklightBrightness(int brightness)throws android.os.RemoteException;

找不到其實現怎麼辦呢？？這是個棘手的問題啊~還好Eclipse很噁心啊~~搜搜就又出來了，這個函數的實現在：

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();            }        }    }

看著看著又模糊啦，這裡怎麼又調用了setBrightness（）哦，此setBrightness非BrightnessPreference.java中的setBrightness。其類屬於：

    private LightsService.Light mLcdLight;

革命尚未成功，你說咋辦，那好吧，為了革命的勝利，再進去看看這個類中setBrightness（）的實現吧。源碼路徑為：

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);            }        }

 

這裡又調用了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);            }        }

 

革命的曙光來啦，看到沒，這裡調用了setLight_native這個本地介面，

private static native void setLight_native(int ptr,int light,int color,int mode,

            int onMS,int offMS,int brightnessMode);

皇天不負有心人啊，勝利的曙光照耀著我們啊，終於就快脫光光啦~~！難以按捺住這顆激動的心啊。

可是這個setLight_native又是在哪裡呢？？經過一番苦苦搜尋，它並不在燈火闌珊處，而是在：

frameworks\base\services\jni\ com_android_server_LightsService.cpp

寬衣，看看：

 

四、JNI層

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，一個函數人家處理的不只是backlight，還有flash，color哦。慚愧啊~

到此，一個美女就這樣被你看完啦~~當然，還有三點哦~~還想要激情的嗎？？激情就在底層了哦。想單刀直入嗎？那還得看你本事了哦~~

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

這句將帶你穿梭進赤裸裸的XX。

五、HAL層

太神奇啦，這裡直接給出HAL層的源碼路勁，如下：

\mediatek\source\hardware\liblights\ lights.c

\hardware\libhardware\include\hardware\ lights.h

你會看到引你越過道德邊緣的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，其實我們需要找的就是set_light_backlight。

static intset_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;}

 

當你認真看完lights.c會發現其基本思想跟之前的設想一樣，只是人家是高手，我是菜鳥，人家看到赤裸裸的美女不是表面，而是藝術~~~~！！

 

 

通過這個分析，可以延伸瞭解到led燈的結構。