雖然這篇文章寫得很差,因爲趕時間,所以就匆匆忙忙地寫出來自己作一個筆記。但是我想對大家應該有一點幫助。
1、有關sensor在Java應用程序的編程(以註冊多個傳感器爲例,這程序是我臨時弄出來的,可能有錯)
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()函數中,調用getSystemService(SENSOR_SERVICE)初始化一個SensorManager實例,爲什麼要用getSystemService函數,而不直接用new SensorManager呢?我們看此函數的實現,在ApplicationContext.java中,
if (SENSOR_SERVICE.equals(name)) {
return getSensorManager();
然後getSensorManager()的實現
private SensorManager getSensorManager() {
synchronized (mSync) {
if (mSensorManager == null) {
mSensorManager = new SensorManager(mMainThread.getHandler().getLooper());
}
}
return mSensorManager;
}
看到沒有?初始化SensorManager的時候需要mMainThread.getHandler().getLooper()這個參數,之個應該是用來傳遞消息用的,在SensorManager類的構造函數中會把此參數傳給類成員mMainLooper。如果用new SensorManager()就需要另外獲取mainLooper參數傳遞進去。
2、在android中跟sensor有關的一些文件有SensorManager.java,位於frameworks/base/core/java/android/hardware目錄下,SensorService.java,位於frameworks/base/services/java/com/android/server目錄下,android_hardware_SensorManager.cpp,位於frameworks/base/core/jni/目錄下,與SensorManager.java相對應,com_android_server_SensorService.cpp,在frameworks/base/services/jni/目錄下,與SensorService.java相對應。還有SystemServer.java文件,Hardware/Libhardware/Include/Hardware目錄下的Sensor.h頭文件。另外我們需要根據Sensor.h實現自己的一個源文件,一般取名爲sensors_xxx.c或者sensors_xxx.cpp。
3、SensorManager類分析
有幾個函數比較重要,必須清晰理解它們的實現,才能瞭解整個傳感器系統的實現。從而更好地去實現硬件抽象層的實現。幾個比較重要的函數有構造函數SensorManager(), registerListener()和unregisterListener(),其中registerListener()和unregisterListener()有多個,標誌爲 @Deprecated的是過時的,就不要看了。
(1)構造函數SensorManager(Looper mainLooper)
這個函數首先獲取得傳感器系統服務,並賦給類成員mSensorService,
mSensorService = ISensorService.Stub.asInterface(
ServiceManager.getService(Context.SENSOR_SERVICE));
這裏我要說一句,就是關於這個傳感器系統服務,很多書上都說用getSystemService()是獲得傳感器的系統服務,而它返回的是SensorManager類型,所以以爲整個系統都是使用同一個SensorManager類的實例,以爲我們在任何地方使用的SensorManager實例都是同一個,它們的公共成員是共享的。但是經過這兩天的分析,這種說法是錯誤的。其實每次調用getSystemService()函數時都初始化一個新的SensorManager實例,而這個SensorManager實例會在構造函數裏通過取得傳感器系統服務SensorService來實現對下層傳感器的一些控制。而這個SensorService纔是系統的傳感器服務,說服務,不如說它只是SensorService類的一個實例罷了。它只在系統初始化時初始化一次。Android中的系統服務機制應該跟傳感器的都差不多一個樣,都是由不同的Manager調用下層相同的Service。你可以列舉其它的Manager。那它是什麼時候初始化呢?它是系統初始化在SystemServer進程裏創建的,SystemServer是一個管理很多系統服務的進程,我們轉到SystemServer.的main函數裏,可以看到一直到調用int2()函數,它會創建一個ServerThread,最終調用AdbSettingsObserver類的run()函數,在run()函數裏有這麼有一句
// Sensor Service is needed by Window Manager, so this goes first
Log.i(TAG, "Sensor Service");
ServiceManager.addService(Context.SENSOR_SERVICE, new SensorService(context));
這裏就創建SensorService實例了。在創建這個實例時會在SensorService構造函數中調用jni函數 public SensorService(Context context) {
if (localLOGV) Log.d(TAG, "SensorService startup");
_sensors_control_init();
}
我們看_sensors_control_init();對應的爲
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;
}
它主要調用了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);
}
之後在系統任何地方使用的都是這個SensorService實例。最後run()函數調用Looper.loop();就進行消息循環等待了,這就是SystemServer進程的消息服務了。這才真正叫做系統服務嘛。
我們繼續看SensorManager類的構造函數,取得SensorService後,
nativeClassInit();
這是一個jni函數,SensorManager類調用的jni函數都在com_android_server_SensorService.cpp裏,我們看這函數
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");
}
這個函數只是獲取和設置一些信息吧,我們不關心。接着
sensors_module_init();
我們看這函數
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;
}
它獲取了sensor的模塊信息,並把它賦給sSensorModule全局變量,之後傳的modules參數都爲這個。
接着在構造函數裏
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);
這裏主要是通過jni函數sensors_module_get_next_sensor(sensor, i);獲取傳感器列表,並把它加入自己的fullList列表中。我們看sensors_module_get_next_sensor()函數
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;
}
它主要是調用HAL層的get_sensors_list()函數取得傳感器列表信息。
接着在sensorManger構造函數最後
sSensorThread = new SensorThread();
創建一個SensorThread()線程。但並未運行,但在SensorThread類的構造函數裏會執行jni函數 sensors_data_init();
我們看此函數static jint
sensors_data_init(JNIEnv *env, jclass clazz)
{
if (sSensorModule == NULL)
return -1;
int err = sensors_data_open(&sSensorModule->common, &sSensorDevice);
return err;
}
它調用了HAL層的sensors_data_open函數,而這個函數位於sensor.h中,它調用的是
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函數。而在SensorThread類的析構函數finalize()裏會調用
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裏
static inline int sensors_data_close(struct sensors_data_device_t* device) {
return device->common.close(&device->common);
}
那什麼時候sSensorThread線程會運行呢?我們在下面看registerListener()函數。
(2) public boolean registerListener(SensorEventListener listener, Sensor sensor, int rate) {
return registerListener(listener, sensor, rate, null);
}
它調用的是 public boolean registerListener(SensorEventListener listener, Sensor sensor, int rate,
Handler handler)
在這函數中,先驗證rate,然後檢測註冊的listener在不在本類的sListeners列表中。
for (ListenerDelegate i : sListeners) {
if (i.getListener() == listener) {
l = i;
break;
}
}
如果不在就申請一個listener,並把它加入全局列表sListener中,並調用mSensorService的enableSensor()函數使能傳感器,這個enableSensor()函數最終會調用HAL層的active函數和set_delay()函數,使用後然後判斷sListener列表是否爲空,當然,第一次爲空時加入一個新的listener就不爲空了,此時就執行sSensorThread的startLocked運行sSensorThread線程了
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,如果註冊的listener在sListeners列表中,則先調用mSensorService的enableSensor()函數使能傳感器,然後把註冊的傳感器加入到已存在的listener中。
result = mSensorService.enableSensor(l, name, handle, delay);
if (result) {
l.addSensor(sensor);
}
接下來我們看看startLocked函數,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爲null,然後它調用了service.getDataChannel()函數,此函數在SensorService類中,主要調用了jni函數_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類中調用的jni函數主要都在com_android_server_SensorService.cpp文件 中,我們看一下這個函數
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;
}
它主要調用了HAL層的open_data_source()函數。取得一些文件描述符等信息。
接下來SensorThread創建一個線程,調用start()就進入SensorThreadRunnable類的run()函數了,所以我們接着去看run()函數,它首先調用open()函數
if (!open()) {
return;
}
在open()函數中調用了 jni函數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);
}
這函數最終調用了HAL層的data_open(),之後run()函數就進入一個while循環了。
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);
}
}
}
}
它調用了jni函數sensors_data_poll()一直讀數據。
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;
}
把傳感器得到的值都放在value數組中,根據返回的傳感器標誌sensor,把它分派給在sListener列表中所有的listener,如果listener中有監聽這個sensor,就把它分派給這個listener,此時就會引起onSensorChange()了。
好了,獲取傳感器數據主要是這樣一個途徑。最後我們去分析一下unregisterListener()函數。
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);
}
}
不用想這個函數會做一些與registerListener相反的事情,至少差不多。它先在sListeners列表中找到這個listener,然後先調用enableSensor()函數禁止這個傳感器。我們跟蹤一下這函數,在SensorService類中。
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;
你們看到它的實現了吧。如果enable是true的話,就調用_sensors_control_activate(),如果是false的話,就調用deactivateIfUnusedLocked(),它們最終都會調用 HAL層的active()函數。最後,如果是禁止傳感器的話,如果mListeners爲空了,它就會調用
_sensors_control_wake();
_sensors_control_close();
這兩個jni函數,最終會調用HAL層的wake()和close_data_source()函數。當調用wake()函數時,會使SensorManager類線程的run()函數中的sensor_data_poll()函數立即返回,此時在run()函數中調用sensors_data_close();最終會調用HAL層的data_close()函數。至此,一個傳感器從初始到結束的流程就分析完了。
所以在java使用一個傳感器在HAL層具體調用的函數流程爲:
首先,sensors_control_open(),只在系統初始化時調用一次。用來初始化control_device結構體。
以下的是每次使用傳感器一般經過的流程,注意,是一般而已,有些並不執行
(1)sensors_data_open
(2)get_sensors_list
(3)activate
(4)set_delay
(5)open_data_source
(6)data_open
(7)poll
一直讀數據。。。。。。。。。。。
退出時
(8)activate
(9)sensors_control_close
(10)data_close
當然其它的細節你們可以繼續去研究。也可以在我博客裏提出來大家交流和討論一下!