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Android相干Sensors的源码总结

热度:79   发布时间:2016-05-01 19:06:27.0
Android有关Sensors的源码总结
下面是一篇关于Android传感器源码总结的文章,讲解得很详细,从Framework到HAL的接口,估计作者没有对sensors的HAL进行研究或者其他原因而没有对HAL更多说明。本人最近项目中有这个模块,先收藏下,以学习!

     

(原文)虽然这篇文章写得很差,因为赶时间,所以就匆匆忙忙地写出来自己作一个笔记。但是我想对大家应该有一点帮助。

1、有关sensor在Java应用程序的编程(以注册多个传感器为例,这程序是我临时弄出来的,可能有错)

package com.sensors.acc;



import android.app.Activity;

import android.os.Bundle;



import android.util.Log;

import android.widget.TextView;

import android.hardware.SensorManager;

import android.hardware.Sensor;

import android.hardware.SensorEvent;

import android.hardware.SensorEventListener;



public class acc extends Activity {

    float x, y, z;

    SensorManager sensormanager = null;

    Sensor accSensor = null;

    Sensor lightSensor = null;

    Sensor proximitySensor = null;

    TextView accTextView = null;

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

    @Override

    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

    sensormanager = (SensorManager)getSystemService(SENSOR_SERVICE);

    accSensor = sensormanager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);

    lightSensor = sensormanager.getDefaultSensor(Sensor.TYPE_LIGHT);

    proximitySensor = sensormanager.getDefaultSensor(Sensor.TYPE_PROXIMITY);

    accTextView = (TextView)findViewById(R.id.textview_name);

    }

  

    SensorEventListener lsn = new SensorEventListener() { 

        public void onSensorChanged(SensorEvent e) {

        if (e.sensor == accSensor) {

             Log.d("sensor", "found acc sensor");

                x = e.values[SensorManager.DATA_X]; 

                y = e.values[SensorManager.DATA_Y]; 

                z = e.values[SensorManager.DATA_Z];

                accTextView.setText("x = " + x + ", /ny = " + y + ", /nz = " + z);

        }

        else if (e.sensor == lightSensor) {

             Log.d("sensor", "found light sensor");

                accTextView.setText("data is " + e.values[0]);

        }

        else if (e.sensor == proximitySensor) {

             Log.d("sensor", "found proximity sensor");

                accTextView.setText("distance is " + e.values[0]);

        }

  //          Log.d("sensor", "found acc sensor");



//           Log.d("sensor", "x = " + x + ", y = " + y + ", z = " + z);

//           accTextView.setText("x = " + x + ", /ny = " + y + ", /nz = " + z);

        } 



        public void onAccuracyChanged(Sensor s, int accuracy) { 

        } 

    };   

    @Override  

    protected void onResume() {      

    super.onResume();      // register this class as a listener for the orientation and accelerometer sensors      

    sensormanager.registerListener(lsn, accSensor, SensorManager.SENSOR_DELAY_NORMAL);

    sensormanager.registerListener(lsn, lightSensor, SensorManager.SENSOR_DELAY_NORMAL);

    sensormanager.registerListener(lsn, proximitySensor, SensorManager.SENSOR_DELAY_NORMAL);

//     sensormanager.unregisterListener(lsn);

    }      

    @Override  

    protected void onStop() {        // unregister listener       

    sensormanager.unregisterListener(lsn, accSensor);

    sensormanager.unregisterListener(lsn, lightSensor);

sensormanager.unregisterListener(lsn, proximitySensor);

    super.onStop();  

    } 

}



在onCreate()函数中,调用getSystemService(SENSOR_SERVICE)初始化一个SensorManager实例,为什么要用getSystemService函数,而不直接用new SensorManager呢?我们看此函数的实现,在ApplicationContext.java中,

if (SENSOR_SERVICE.equals(name)) {

            return getSensorManager();

然后getSensorManager()的实现


    private SensorManager getSensorManager() {

        synchronized (mSync) {

            if (mSensorManager == null) {

                mSensorManager = new SensorManager(mMainThread.getHandler().getLooper());

            }

        }

        return mSensorManager;

}

看到没有?初始化SensorManager的时候需要mMainThread.getHandler().getLooper()这个参数,之个应该是用来传递消息用的,在SensorManager类的构造函数中会把此参数传给类成员mMainLooper。如果用new SensorManager()就需要另外获取mainLooper参数传递进去。



2、在android中跟sensor有关的一些文件有SensorManager.java,位于frameworks/base/core/java/android/hardware目录下,SensorService.java,位于frameworks/base/services/java/com/android/server目录下,android_hardware_SensorManager.cpp,位于frameworks/base/core/jni/目录下,与SensorManager.java相对应,com_android_server_SensorService.cpp,在frameworks/base/services/jni/目录下,与SensorService.java相对应。还有SystemServer.java文件,Hardware/Libhardware/Include/Hardware目录下的Sensor.h头文件。另外我们需要根据Sensor.h实现自己的一个源文件,一般取名为sensors_xxx.c或者sensors_xxx.cpp。



3、SensorManager类分析

有几个函数比较重要,必须清晰理解它们的实现,才能了解整个传感器系统的实现。从而更好地去实现硬件抽象层的实现。几个比较重要的函数有构造函数SensorManager(), registerListener()和unregisterListener(),其中registerListener()和unregisterListener()有多个,标志为 @Deprecated的是过时的,就不要看了。

(1)构造函数SensorManager(Looper mainLooper)

这个函数首先获取得传感器系统服务,并赋给类成员mSensorService,

       mSensorService = ISensorService.Stub.asInterface(

                ServiceManager.getService(Context.SENSOR_SERVICE));

这里我要说一句,就是关于这个传感器系统服务,很多书上都说用getSystemService()是获得传感器的系统服务,而它返回的是SensorManager类型,所以以为整个系统都是使用同一个SensorManager类的实例,以为我们在任何地方使用的SensorManager实例都是同一个,它们的公共成员是共享的。但是经过这两天的分析,这种说法是错误的。其实每次调用getSystemService()函数时都初始化一个新的SensorManager实例,而这个SensorManager实例会在构造函数里通过取得传感器系统服务SensorService来实现对下层传感器的一些控制。而这个SensorService才是系统的传感器服务,说服务,不如说它只是SensorService类的一个实例罢了。它只在系统初始化时初始化一次。Android中的系统服务机制应该跟传感器的都差不多一个样,都是由不同的Manager调用下层相同的Service。你可以列举其它的Manager。那它是什么时候初始化呢?它是系统初始化在SystemServer进程里创建的,SystemServer是一个管理很多系统服务的进程,我们转到SystemServer.的main函数里,可以看到一直到调用int2()函数,它会创建一个ServerThread,最终调用AdbSettingsObserver类的run()函数,在run()函数里有这么有一句

            // Sensor Service is needed by Window Manager, so this goes first

            Log.i(TAG, "Sensor Service");

            ServiceManager.addService(Context.SENSOR_SERVICE, new SensorService(context));

这里就创建SensorService实例了。在创建这个实例时会在SensorService构造函数中调用jni函数    public SensorService(Context context) {

        if (localLOGV) Log.d(TAG, "SensorService startup");

        _sensors_control_init();

    }

我们看_sensors_control_init();对应的为

static jint

android_init(JNIEnv *env, jclass clazz)

{

    sensors_module_t* module;

    if (hw_get_module(SENSORS_HARDWARE_MODULE_ID, (const hw_module_t**)&module) == 0) {

        if (sensors_control_open(&module->common, &sSensorDevice) == 0) {

            const struct sensor_t* list;

            int count = module->get_sensors_list(module, &list);

            return count;

        }

    }

    return 0;

}

它主要调用了sensor.h中的sensors_control_open()

static inline int sensors_control_open(const struct hw_module_t* module,

        struct sensors_control_device_t** device) {

    return module->methods->open(module,

            SENSORS_HARDWARE_CONTROL, (struct hw_device_t**)device);

}

之后在系统任何地方使用的都是这个SensorService实例。最后run()函数调用Looper.loop();就进行消息循环等待了,这就是SystemServer进程的消息服务了。这才真正叫做系统服务嘛。



我们继续看SensorManager类的构造函数,取得SensorService后,

               nativeClassInit();

这是一个jni函数,SensorManager类调用的jni函数都在com_android_server_SensorService.cpp里,我们看这函数

static void

nativeClassInit (JNIEnv *_env, jclass _this)

{

    jclass sensorClass = _env->FindClass("android/hardware/Sensor");

    SensorOffsets& sensorOffsets = gSensorOffsets;

    sensorOffsets.name        = _env->GetFieldID(sensorClass, "mName",      "Ljava/lang/String;");

    sensorOffsets.vendor      = _env->GetFieldID(sensorClass, "mVendor",    "Ljava/lang/String;");

    sensorOffsets.version     = _env->GetFieldID(sensorClass, "mVersion",   "I");

    sensorOffsets.handle      = _env->GetFieldID(sensorClass, "mHandle",    "I");

    sensorOffsets.type        = _env->GetFieldID(sensorClass, "mType",      "I");

    sensorOffsets.range       = _env->GetFieldID(sensorClass, "mMaxRange",  "F");

    sensorOffsets.resolution  = _env->GetFieldID(sensorClass, "mResolution","F");

    sensorOffsets.power       = _env->GetFieldID(sensorClass, "mPower",     "F");

}

这个函数只是获取和设置一些信息吧,我们不关心。接着

                sensors_module_init();

我们看这函数

static jint

sensors_module_init(JNIEnv *env, jclass clazz)

{

    int err = 0;

    sensors_module_t const* module;

    err = hw_get_module(SENSORS_HARDWARE_MODULE_ID, (const hw_module_t **)&module);

    if (err == 0)

        sSensorModule = (sensors_module_t*)module;

    return err;

}

它获取了sensor的模块信息,并把它赋给sSensorModule全局变量,之后传的modules参数都为这个。

接着在构造函数里

            final ArrayList<Sensor> fullList = sFullSensorsList;

                int i = 0;

                do {

                    Sensor sensor = new Sensor();

                    i = sensors_module_get_next_sensor(sensor, i);



                    if (i>=0) {

                        Log.d(TAG, "found sensor: " + sensor.getName() +

                                ", handle=" + sensor.getHandle());

                        sensor.setLegacyType(getLegacySensorType(sensor.getType()));

                        fullList.add(sensor);

                        sHandleToSensor.append(sensor.getHandle(), sensor);

                    }

                } while (i>0);

这里主要是通过jni函数sensors_module_get_next_sensor(sensor, i);获取传感器列表,并把它加入自己的fullList列表中。我们看sensors_module_get_next_sensor()函数

static jint

sensors_module_get_next_sensor(JNIEnv *env, jobject clazz, jobject sensor, jint next)

{

    if (sSensorModule == NULL)

        return 0;



    SensorOffsets& sensorOffsets = gSensorOffsets;

    const struct sensor_t* list;

    int count = sSensorModule->get_sensors_list(sSensorModule, &list);

    if (next >= count)

        return -1;

  

    list += next;



    jstring name = env->NewStringUTF(list->name);

    jstring vendor = env->NewStringUTF(list->vendor);

    env->SetObjectField(sensor, sensorOffsets.name,      name);

    env->SetObjectField(sensor, sensorOffsets.vendor,    vendor);

    env->SetIntField(sensor, sensorOffsets.version,      list->version);

    env->SetIntField(sensor, sensorOffsets.handle,       list->handle);

    env->SetIntField(sensor, sensorOffsets.type,         list->type);

    env->SetFloatField(sensor, sensorOffsets.range,      list->maxRange);

    env->SetFloatField(sensor, sensorOffsets.resolution, list->resolution);

    env->SetFloatField(sensor, sensorOffsets.power,      list->power);

  

    next++;

    return next<count ? next : 0;

}

它主要是调用HAL层的get_sensors_list()函数取得传感器列表信息。

接着在sensorManger构造函数最后

                sSensorThread = new SensorThread();

创建一个SensorThread()线程。但并未运行,但在SensorThread类的构造函数里会执行jni函数            sensors_data_init();

我们看此函数static jint

sensors_data_init(JNIEnv *env, jclass clazz)

{

    if (sSensorModule == NULL)

        return -1;

    int err = sensors_data_open(&sSensorModule->common, &sSensorDevice);

    return err;

}

它调用了HAL层的sensors_data_open函数,而这个函数位于sensor.h中,它调用的是

static inline int sensors_data_open(const struct hw_module_t* module,

        struct sensors_data_device_t** device) {

    return module->methods->open(module,

            SENSORS_HARDWARE_DATA, (struct hw_device_t**)device);

}

Modules->methods->open函数。而在SensorThread类的析构函数finalize()里会调用

            sensors_data_uninit();

static jint

sensors_data_uninit(JNIEnv *env, jclass clazz)

{

    int err = 0;

    if (sSensorDevice) {

        err = sensors_data_close(sSensorDevice);

        if (err == 0)

            sSensorDevice = 0;

    }

    return err;

}

在sensor.h里

static inline int sensors_data_close(struct sensors_data_device_t* device) {

    return device->common.close(&device->common);

}

那什么时候sSensorThread线程会运行呢?我们在下面看registerListener()函数。



(2)    public boolean registerListener(SensorEventListener listener, Sensor sensor, int rate) {

        return registerListener(listener, sensor, rate, null);

}

它调用的是    public boolean registerListener(SensorEventListener listener, Sensor sensor, int rate,

            Handler handler)

在这函数中,先验证rate,然后检测注册的listener在不在本类的sListeners列表中。

                for (ListenerDelegate i : sListeners) {

                    if (i.getListener() == listener) {

                        l = i;

                        break;

                    }

                }

如果不在就申请一个listener,并把它加入全局列表sListener中,并调用mSensorService的enableSensor()函数使能传感器,这个enableSensor()函数最终会调用HAL层的active函数和set_delay()函数,使用后然后判断sListener列表是否为空,当然,第一次为空时加入一个新的listener就不为空了,此时就执行sSensorThread的startLocked运行sSensorThread线程了

          l = new ListenerDelegate(listener, sensor, handler);

                    result = mSensorService.enableSensor(l, name, handle, delay);

                    if (result) {

                        sListeners.add(l);

                        sListeners.notify();

                    }

                    if (!sListeners.isEmpty()) {

                        sSensorThread.startLocked(mSensorService);

                    }

另一方面,如果注册的listener在sListeners列表中,则先调用mSensorService的enableSensor()函数使能传感器,然后把注册的传感器加入到已存在的listener中。

                 result = mSensorService.enableSensor(l, name, handle, delay);

                    if (result) {

                        l.addSensor(sensor);

                    }

接下来我们看看startLocked函数,它在SensorThread中,

        void startLocked(ISensorService service) {

            try {

                if (mThread == null) {

                    Bundle dataChannel = service.getDataChannel();

                    mThread = new Thread(new SensorThreadRunnable(dataChannel),

                            SensorThread.class.getName());

                    mThread.start();

                }

            } catch (RemoteException e) {

                Log.e(TAG, "RemoteException in startLocked: ", e);

            }

        }

第一次mThread为null,然后它调用了service.getDataChannel()函数,此函数在SensorService类中,主要调用了jni函数_sensors_control_open(),

    public Bundle getDataChannel() throws RemoteException {

        // synchronize so we do not require sensor HAL to be thread-safe.

        synchronized(mListeners) {

            return _sensors_control_open();

        }

}

SensorService类中调用的jni函数主要都在com_android_server_SensorService.cpp文件 中,我们看一下这个函数

static jobject

android_open(JNIEnv *env, jclass clazz)

{

    native_handle_t* handle = sSensorDevice->open_data_source(sSensorDevice);

    if (!handle) {

        return NULL;

    }



    // new Bundle()

    jobject bundle = env->NewObject(

            gBundleOffsets.mClass,

            gBundleOffsets.mConstructor);



    if (handle->numFds > 0) {

        jobjectArray fdArray = env->NewObjectArray(handle->numFds,

                gParcelFileDescriptorOffsets.mClass, NULL);

        for (int i = 0; i < handle->numFds; i++) {

            // new FileDescriptor()

            jobject fd = env->NewObject(gFileDescriptorOffsets.mClass,

                    gFileDescriptorOffsets.mConstructor);

            env->SetIntField(fd, gFileDescriptorOffsets.mDescriptor, handle->data[i]);

            // new ParcelFileDescriptor()

            jobject pfd = env->NewObject(gParcelFileDescriptorOffsets.mClass,

                    gParcelFileDescriptorOffsets.mConstructor, fd);

            env->SetObjectArrayElement(fdArray, i, pfd);

        }

        // bundle.putParcelableArray("fds", fdArray);

        env->CallVoidMethod(bundle, gBundleOffsets.mPutParcelableArray,

                env->NewStringUTF("fds"), fdArray);

    }



    if (handle->numInts > 0) {

        jintArray intArray = env->NewIntArray(handle->numInts);

        env->SetIntArrayRegion(intArray, 0, handle->numInts, &handle->data[handle->numInts]);

        // bundle.putIntArray("ints", intArray);

        env->CallVoidMethod(bundle, gBundleOffsets.mPutIntArray,

                env->NewStringUTF("ints"), intArray);

    }



    // delete the file handle, but don't close any file descriptors

    native_handle_delete(handle);

    return bundle;

}

它主要调用了HAL层的open_data_source()函数。取得一些文件描述符等信息。

接下来SensorThread创建一个线程,调用start()就进入SensorThreadRunnable类的run()函数了,所以我们接着去看run()函数,它首先调用open()函数

                if (!open()) {

                    return;

                }

在open()函数中调用了  jni函数sensors_data_open(fds, ints);

static jint

sensors_data_open(JNIEnv *env, jclass clazz, jobjectArray fdArray, jintArray intArray)

{

    jclass FileDescriptor = env->FindClass("java/io/FileDescriptor");

    jfieldID fieldOffset = env->GetFieldID(FileDescriptor, "descriptor", "I");

    int numFds = (fdArray ? env->GetArrayLength(fdArray) : 0);

    int numInts = (intArray ? env->GetArrayLength(intArray) : 0);

    native_handle_t* handle = native_handle_create(numFds, numInts);

    int offset = 0;



    for (int i = 0; i < numFds; i++) {

        jobject fdo = env->GetObjectArrayElement(fdArray, i);

        if (fdo) {

            handle->data[offset++] = env->GetIntField(fdo, fieldOffset);

        } else {

            handle->data[offset++] = -1;

        }

    }

    if (numInts > 0) {

        jint* ints = env->GetIntArrayElements(intArray, 0);

        for (int i = 0; i < numInts; i++) {

            handle->data[offset++] = ints[i];

        }

        env->ReleaseIntArrayElements(intArray, ints, 0);

    }



    // doesn't take ownership of the native handle

    return sSensorDevice->data_open(sSensorDevice, handle);

}

这函数最终调用了HAL层的data_open(),之后run()函数就进入一个while循环了。

         while (true) {

                    // wait for an event

                    final int sensor = sensors_data_poll(values, status, timestamp);



                    int accuracy = status[0];

                    synchronized (sListeners) {

                        if (sensor == -1 || sListeners.isEmpty()) {

                            if (sensor == -1) {

                                // we lost the connection to the event stream. this happens

                                // when the last listener is removed.

                                Log.d(TAG, "_sensors_data_poll() failed, we bail out.");

                            }



                            // we have no more listeners or polling failed, terminate the thread

                            sensors_data_close();

                            mThread = null;

                            break;

                        }

                        final Sensor sensorObject = sHandleToSensor.get(sensor);

                        if (sensorObject != null) {

                            // report the sensor event to all listeners that

                            // care about it.

                            final int size = sListeners.size();

                            for (int i=0 ; i<size ; i++) {

                                ListenerDelegate listener = sListeners.get(i);

                                if (listener.hasSensor(sensorObject)) {

                                    // this is asynchronous (okay to call

                                    // with sListeners lock held).

                                    listener.onSensorChangedLocked(sensorObject,

                                            values, timestamp, accuracy);

                                }

                            }

                        }

                    }

它调用了jni函数sensors_data_poll()一直读数据。

static jint

sensors_data_poll(JNIEnv *env, jclass clazz,

        jfloatArray values, jintArray status, jlongArray timestamp)

{

    sensors_data_t data;

    int res = sSensorDevice->poll(sSensorDevice, &data);

    if (res >= 0) {

        jint accuracy = data.vector.status;

        env->SetFloatArrayRegion(values, 0, 3, data.vector.v);

        env->SetIntArrayRegion(status, 0, 1, &accuracy);

        env->SetLongArrayRegion(timestamp, 0, 1, &data.time);

    }



    return res;

}

把传感器得到的值都放在value数组中,根据返回的传感器标志sensor,把它分派给在sListener列表中所有的listener,如果listener中有监听这个sensor,就把它分派给这个listener,此时就会引起onSensorChange()了。



好了,获取传感器数据主要是这样一个途径。最后我们去分析一下unregisterListener()函数。

   private void unregisterListener(Object listener) {

        if (listener == null) {

            return;

        }

        try {

            synchronized (sListeners) {

                final int size = sListeners.size();

                for (int i=0 ; i<size ; i++) {

                    ListenerDelegate l = sListeners.get(i);

                    if (l.getListener() == listener) {

                        // disable all sensors for this listener

                        for (Sensor sensor : l.getSensors()) {

                            String name = sensor.getName();

                            int handle = sensor.getHandle();

                            mSensorService.enableSensor(l, name, handle, SENSOR_DISABLE);

                        }

                        sListeners.remove(i);

                        break;

                    }

                }

            }

        } catch (RemoteException e) {

            Log.e(TAG, "RemoteException in unregisterListener: ", e);

        }

}

不用想这个函数会做一些与registerListener相反的事情,至少差不多。它先在sListeners列表中找到这个listener,然后先调用enableSensor()函数禁止这个传感器。我们跟踪一下这函数,在SensorService类中。

      synchronized(mListeners) {

            if (enable!=SENSOR_DISABLE && !_sensors_control_activate(sensor, true)) {

                Log.w(TAG, "could not enable sensor " + sensor);

                return false;

            }

                  

            Listener l = null;

            int minDelay = enable;

            for (Listener listener : mListeners) {

                if (binder == listener.mToken) {

                    l = listener;

                }

                if (minDelay > listener.mDelay)

                    minDelay = listener.mDelay;

            }

          

            if (l == null && enable!=SENSOR_DISABLE) {

                l = new Listener(binder);

                binder.linkToDeath(l, 0);

                mListeners.add(l);

                mListeners.notify();

            }

          

            if (l == null) {

                // by construction, this means we're disabling a listener we

                // don't know about...

                Log.w(TAG, "listener with binder " + binder +

                        ", doesn't exist (sensor=" + name + ", id=" + sensor + ")");

                return false;

            }

          

            if (minDelay >= 0) {

                _sensors_control_set_delay(minDelay);

            }

          

            if (enable != SENSOR_DISABLE) {

                l.addSensor(sensor, enable);

            } else {

                l.removeSensor(sensor);

                deactivateIfUnusedLocked(sensor);

                if (l.mSensors == 0) {

                    mListeners.remove(l);

                    binder.unlinkToDeath(l, 0);

                    mListeners.notify();

                }

            }

          

            if (mListeners.size() == 0) {

                _sensors_control_wake();

                _sensors_control_close();

            }

        }      

        return true;

你们看到它的实现了吧。如果enable是true的话,就调用_sensors_control_activate(),如果是false的话,就调用deactivateIfUnusedLocked(),它们最终都会调用 HAL层的active()函数。最后,如果是禁止传感器的话,如果mListeners为空了,它就会调用

_sensors_control_wake();

                _sensors_control_close();

这两个jni函数,最终会调用HAL层的wake()和close_data_source()函数。当调用wake()函数时,会使SensorManager类线程的run()函数中的sensor_data_poll()函数立即返回,此时在run()函数中调用sensors_data_close();最终会调用HAL层的data_close()函数。至此,一个传感器从初始到结束的流程就分析完了。

       所以在java使用一个传感器在HAL层具体调用的函数流程为:

首先,sensors_control_open(),只在系统初始化时调用一次。用来初始化control_device结构体。

以下的是每次使用传感器一般经过的流程,注意,是一般而已,有些并不执行

(1)sensors_data_open

(2)get_sensors_list

(3)activate

(4)set_delay

(5)open_data_source

(6)data_open

(7)poll

一直读数据。。。。。。。。。。。

退出时

(8)activate

(9)sensors_control_close

(10)data_close


原文:http://blog.csdn.net/JerryMo06/archive/2010/04/15/5487476.aspx
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