学步园

1. 简介

    在了解Sensor工作流程以前，一直以为其事件是通过Event Hub来进行输送的，可是研究完Android4.0代码之后，才发现自己错了。

    其主要框架如下图所示：

 

2.功能模块

2.1 SensorManager.java

与下层接口功能：
1) 在SensorManager函数中
   (1) 调用native sensors_module_init初始化sensor list，即实例化native中的SensorManager

   (2) 创建SensorThread线程

2) 在类SensorThread中
   (1) 调用native sensors_create_queue创建队列
   (2) 在线程中dead loop地调用native sensors_data_poll以从队列sQueue中获取事件(float[] values = new float[3];)
   (3) 收到事件之后，报告sensor event给所有注册且关心此事件的listener

 

与上层的接口功能：

1) 在onPause时取消listener注册

2) 在onResume时注册listener

3) 把收到的事件报告给注册的listener

2.2 android_hardware_SensorManager.cpp

      实现SensorManager.java中的native函数，它主要调用SenrsorManager.cpp和SensorEventQueue.cpp中的类来完成相关的工作。

2.3 SensorManager.cpp

class SensorManager :
    public ASensorManager,
    public Singleton<SensorManager>
{
public:
    SensorManager(); //调用assertStateLocked
    ~SensorManager();
    //调用assertStateLocked,并返回mSensorList
    ssize_t getSensorList(Sensor const* const** list) const;

    // 返回mSensorList中第一个类型与type一致的sensor	
    Sensor const* getDefaultSensor(int type);

    // 调用mSensorServer->createSensorEventConnection创建一个连接(ISensorEventConnection)
    // 并用此连接做为参数创建一个SensorEventQueue对象并返回
    sp<SensorEventQueue> createEventQueue();

private:
    // DeathRecipient interface
    void sensorManagerDied();
    // 调用getService获取SensorService客户端并保存在mSensorServer中
    // 调用mSensorServer->getSensorList获取sensor列表，并保存在mSensors和mSensorList中
    status_t assertStateLocked() const;

private:
    mutable Mutex mLock;
    mutable sp<ISensorServer> mSensorServer; // SensorService客户端
    mutable Sensor const** mSensorList; // sensor列表
    mutable Vector<Sensor> mSensors;    // sensor列表
    mutable sp<IBinder::DeathRecipient> mDeathObserver;
}

 

class ISensorEventConnection : public IInterface
{
public:
    DECLARE_META_INTERFACE(SensorEventConnection);

    virtual sp<SensorChannel> getSensorChannel() const = 0;
    virtual status_t enableDisable(int handle, bool enabled) = 0;
    virtual status_t setEventRate(int handle, nsecs_t ns) = 0;
};

2.4 SensorService.cpp

       SensorService作为一个轻量级的system service，它运行于SystemServer内，即在system_init<system_init.cpp>调用SensorService::instantiate();

      SensorService主要功能如下：
          1) SensorService::instantiate创建实例对象，并增加到ServiceManager中，且创建并启动线程，并执行threadLoop
          2) threadLoop从sensor驱动获取原始数据，然后通过SensorEventConnection把事件发送给客户端
          3) BnSensorServer的成员函数负责让客户端获取sensor列表和创建SensorEventConnection

      SensorService与客户端的接口定义如下：

class ISensorServer : public IInterface
{
public:
    DECLARE_META_INTERFACE(SensorServer);

    virtual Vector<Sensor> getSensorList() = 0;
    virtual sp<ISensorEventConnection> createSensorEventConnection() = 0;
};

    SensorService定义如下：

class SensorService :
        public BinderService<SensorService>, //创建SensorService对象，并增加到ServiceManager中
        public BnSensorServer, // 申明了SensorService与客户端(SensorManager)间的binder接口
        protected Thread // 线程辅助类，调用run创建并启动线程，然后在线程主函数内回调threadLoop函数,
                         // 所以在使用它时，做一个派生，并根据需要重写threadLoop即可
                    
{
   friend class BinderService<SensorService>;

   static const nsecs_t MINIMUM_EVENTS_PERIOD =   1000000; // 1000 Hz

            SensorService();
    virtual ~SensorService();
   
    /*
    在addService时，第一次构建sp强引用对象时，会调用onFirstRef函数
     实现功能如下：
     1) 获取SensorDevice实例
     2) 调用SensorDevice.getSensorList获取sensor_t列表
     3) 根据硬件sensor_t创建HardwareSensor,然后加入mSensorList(Sensor)
            和mSensorMap(HardwareSensor)中
     4) 根据硬件sensor_t创建对应的senosr(如GravitySensor),
            然后加入mVirtualSensorList和mSensorList中
     5) mUserSensorList = mSensorList;
     6) run("SensorService", PRIORITY_URGENT_DISPLAY);运行线程，并执行threadLoop
    */
    virtual void onFirstRef(); 

    // Thread interface
    /*
      1) 调用SensorDevice.poll获取sensors_event_t事件
      2) 获取已经激活的sensor列表mActiveVirtualSensors
      3) 对每一个事件，执行SensorFusion.process
      4) 对每一个事件，执行HardwareSensor.process(事件无变化,直接copy)
      5) 调用SensorService::SensorEventConnection::sendEvents，把事件发
             送给所有的listener
    */
    virtual bool threadLoop();

    // ISensorServer interface
    // 返回mUserSensorList
    virtual Vector<Sensor> getSensorList();
    
    // 实例化SensorEventConnection并返回
    virtual sp<ISensorEventConnection> createSensorEventConnection();

    virtual status_t dump(int fd, const Vector<String16>& args);

    //====================================================================
    //============== SensorEventConnection  start ========================
    class SensorEventConnection : public BnSensorEventConnection {

        virtual ~SensorEventConnection();
        virtual void onFirstRef();

	// 返回mChannel
        virtual sp<SensorChannel> getSensorChannel() const;

	// 调用SensorService::enable或SensorService::disable
        virtual status_t enableDisable(int handle, bool enabled);

        // 调用SensorService::setEventRate
        virtual status_t setEventRate(int handle, nsecs_t ns);

        sp<SensorService> const mService; // 保存当前SensorService实例
        sp<SensorChannel> const mChannel; // SensorChannel实例
        mutable Mutex mConnectionLock;

        // protected by SensorService::mLock
        SortedVector<int> mSensorInfo;

    public:
        /*
          1) 把当前service保存在mService中
          2) 创建SensorChannel实例，并保存在mChannel中
             (在SensorChannel::SensorChannel中创建pipe,并把收和发都设置非阻塞)
        */
        SensorEventConnection(const sp<SensorService>& service);

        // 调用连接中的mChannel->write (SensorChannel::write),把符合条件的事件写入pipe
        status_t sendEvents(sensors_event_t const* buffer, size_t count,
                sensors_event_t* scratch = NULL);

        bool hasSensor(int32_t handle) const; //检查handle是否在mSensorInfo中
        bool hasAnySensor() const;   //检查mSensorInfo中是否有sensor
        bool addSensor(int32_t handle); //把handle增加到mSensorInfo列表中
        bool removeSensor(int32_t handle); //把handle从mSensorInfo中删除
    };
    //============== SensorEventConnection  end ========================
    //====================================================================

    class SensorRecord {
        SortedVector< wp<SensorEventConnection> > mConnections;
    public:
        SensorRecord(const sp<SensorEventConnection>& connection);
        bool addConnection(const sp<SensorEventConnection>& connection);
        bool removeConnection(const wp<SensorEventConnection>& connection);
        size_t getNumConnections() const { return mConnections.size(); }
    };

    SortedVector< wp<SensorEventConnection> > getActiveConnections() const;
    DefaultKeyedVector<int, SensorInterface*> getActiveVirtualSensors() const;

    String8 getSensorName(int handle) const;
    void recordLastValue(sensors_event_t const * buffer, size_t count);
    static void sortEventBuffer(sensors_event_t* buffer, size_t count);
    void registerSensor(SensorInterface* sensor);
    void registerVirtualSensor(SensorInterface* sensor);

    // constants
    Vector<Sensor> mSensorList;  // Sensor列表
    Vector<Sensor> mUserSensorList; //与mSensorList一样
    DefaultKeyedVector<int, SensorInterface*> mSensorMap; //其成员为HardwareSensor
    Vector<SensorInterface *> mVirtualSensorList; //其成员为HardwareSensor
    status_t mInitCheck;

    // protected by mLock
    mutable Mutex mLock;
    DefaultKeyedVector<int, SensorRecord*> mActiveSensors; //成员为SensorRecord
    DefaultKeyedVector<int, SensorInterface*> mActiveVirtualSensors; //成员为HardwareSensor
    SortedVector< wp<SensorEventConnection> > mActiveConnections;

    // The size of this vector is constant, only the items are mutable
    KeyedVector<int32_t, sensors_event_t> mLastEventSeen;

public:
    static char const* getServiceName() { return "sensorservice"; }

    void cleanupConnection(SensorEventConnection* connection);

    /*
      1) 调用HardwareSensor::activate，即SensorDevice::activate
      2) 然后创建SensorRecord并增加到列表mActiveSensors
      3) 把此HardwareSensor增加到连接的mSensorInfo
      4) 把此连接增加到mActiveConnections中
    */
    status_t enable(const sp<SensorEventConnection>& connection, int handle);

    /*
       1) 把此sensor从连接的mSensorInfo中删除
       2) 把此连接从mActiveConnections中删除
       3) 调用HardwareSensor::activate，即SensorDevice::activate
    */
    status_t disable(const sp<SensorEventConnection>& connection, int handle);
    /*
       1)调用HardwareSensor::setDelay，即SensorDevice::setDelay
     */
    status_t setEventRate(const sp<SensorEventConnection>& connection, int handle, nsecs_t ns);
}

2.5 SensorDevice.cpp

      SensorDevice封装了对SensorHAL层代码的调用，主要包含以下功能：
         1) 获取sensor列表(getSensorList)
         2) 获取sensor事件(poll)
         3) Enable或Disable sensor (activate)
         4) 设置delay时间

 

class SensorDevice : public Singleton<SensorDevice> {

    friend class Singleton<SensorDevice>;

    struct sensors_poll_device_t* mSensorDevice; // sensor设备

    struct sensors_module_t* mSensorModule;

    mutable Mutex mLock; // protect mActivationCount[].rates
    // fixed-size array after construction
    struct Info {
        Info() : delay(0) { }
        KeyedVector<void*, nsecs_t> rates;
        nsecs_t delay;
        status_t setDelayForIdent(void* ident, int64_t ns);
        nsecs_t selectDelay();
    };
    DefaultKeyedVector<int, Info> mActivationCount;

    /*
      1) 调用hw_get_module(SENSORS_HARDWARE_MODULE_ID,..)获取sensors_module_t，
             并保存在mSensorModule中
      2) 调用mSensorModule->common->methods->open,以返回sensors_poll_device_t,
             并保存在mSensorDevice中
      3) 调用mSensorModule->get_sensors_list所有可访问的sensor_t
      4) 调用mSensorDevice->activate激活所有的sensor
    */
    SensorDevice();
public:
    // 调用mSensorModule->get_sensors_list实现
    ssize_t getSensorList(sensor_t const** list);

    status_t initCheck() const;

    // 调用mSensorDevice->poll实现
    ssize_t poll(sensors_event_t* buffer, size_t count);

    // 调用mSensorDevice->activate实现
    status_t activate(void* ident, int handle, int enabled);
    
    // 调用mSensorDevice->setDelay实现
    status_t setDelay(void* ident, int handle, int64_t ns);
    void dump(String8& result, char* buffer, size_t SIZE);
};

2.6 Sensor HAL

定义：/hardware/libhardware/include/hardware/sensors.h

实现：/hardware/mychip/sensor/st/sensors.c

2.6.1 struct sensors_poll_device_t 定义     

struct sensors_poll_device_t {
    struct hw_device_t common;

    // Activate/deactivate one sensor.
    int (*activate)(struct sensors_poll_device_t *dev,
            int handle, int enabled);

    // Set the delay between sensor events in nanoseconds for a given sensor.
    int (*setDelay)(struct sensors_poll_device_t *dev,
            int handle, int64_t ns);

    // Returns an array of sensor data.
    int (*poll)(struct sensors_poll_device_t *dev,
            sensors_event_t* data, int count);
};

2.6.2 struct sensors_module_t  定义

struct sensors_module_t {
    struct hw_module_t common;

    /**
     * Enumerate all available sensors. The list is returned in "list".
     * @return number of sensors in the list
     */
    int (*get_sensors_list)(struct sensors_module_t* module,
            struct sensor_t const** list);
};

2.6.3  struct sensor_t 定义

struct sensor_t {
    /* name of this sensors */
    const char*     name;
    /* vendor of the hardware part */
    const char*     vendor;
    /* version of the hardware part + driver. The value of this field
     * must increase when the driver is updated in a way that changes the
     * output of this sensor. This is important for fused sensors when the
     * fusion algorithm is updated.
     */    
    int             version;
    /* handle that identifies this sensors. This handle is used to activate
     * and deactivate this sensor. The value of the handle must be 8 bits
     * in this version of the API. 
     */
    int             handle;
    /* this sensor's type. */
    int             type;
    /* maximaum range of this sensor's value in SI units */
    float           maxRange;
    /* smallest difference between two values reported by this sensor */
    float           resolution;
    /* rough estimate of this sensor's power consumption in mA */
    float           power;
    /* minimum delay allowed between events in microseconds. A value of zero
     * means that this sensor doesn't report events at a constant rate, but
     * rather only when a new data is available */
    int32_t         minDelay;
    /* reserved fields, must be zero */
    void*           reserved[8];
};

2.6.4 struct sensors_event_t 定义

typedef struct {
    union {
        float v[3];
        struct {
            float x;
            float y;
            float z;
        };
        struct {
            float azimuth;
            float pitch;
            float roll;
        };
    };
    int8_t status;
    uint8_t reserved[3];
} sensors_vec_t;

/**
 * Union of the various types of sensor data
 * that can be returned.
 */
typedef struct sensors_event_t {
    /* must be sizeof(struct sensors_event_t) */
    int32_t version;

    /* sensor identifier */
    int32_t sensor;

    /* sensor type */
    int32_t type;

    /* reserved */
    int32_t reserved0;

    /* time is in nanosecond */
    int64_t timestamp;

    union {
        float           data[16];

        /* acceleration values are in meter per second per second (m/s^2) */
        sensors_vec_t   acceleration;

        /* magnetic vector values are in micro-Tesla (uT) */
        sensors_vec_t   magnetic;

        /* orientation values are in degrees */
        sensors_vec_t   orientation;

        /* gyroscope values are in rad/s */
        sensors_vec_t   gyro;

        /* temperature is in degrees centigrade (Celsius) */
        float           temperature;

        /* distance in centimeters */
        float           distance;

        /* light in SI lux units */
        float           light;

        /* pressure in hectopascal (hPa) */
        float           pressure;

        /* relative humidity in percent */
        float           relative_humidity;
    };
    uint32_t        reserved1[4];
} sensors_event_t;

2.6.5 struct sensors_module_t 实现

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