Android中背光系统架构
Mg Android中背光系统架构
Email:[email protected]
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
#include
#include
#include
#include
#include
//#include
//#include
#include
#include
#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。