Android Sensor 4 - Sensor Device

浏览数：21 / 时间：2015年06月11日

Sensor本地封装类SensorDevice

SensorDevice是在本地代码中SensorService对Sensor设备的抽象类型封装，它封装了传感器硬件的硬件操作，该类继承了Singleton类，通过getInstance方法获得单例模式设备操作对象：

@frameworks/base/services/sensorservice/SensorDevice.h

class SensorDevice : public Singleton<SensorDevice> {
    friend class Singleton<SensorDevice>;
    struct sensors_poll_device_t* mSensorDevice;
    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;
　  SensorDevice();
public:
    ssize_t getSensorList(sensor_t const** list);
    status_t initCheck() const;
    ssize_t poll(sensors_event_t* buffer, size_t count);
    status_t activate(void* ident, int handle, int enabled);
    status_t setDelay(void* ident, int handle, int64_t ns);
    void dump(String8& result, char* buffer, size_t SIZE);
};

通过SensorDevice类的定义可看到它包含的属性和方法：

属性：

mSensorDevice：Sensor设备HAL层操作接口封装结构

mSensorModule：Sensor设备HAL硬件模块封装结构

mActivationCount：保存激活Sensor设备向量表

方法：

SensorDevice：构造方法

getSensorList：获得Sensor设备列表方法

poll：Sensor设备多路监听方法

activate：设备激活方法

setDelay：设备Sensor设备延迟方法

由前面分析可知，SensorDevice是单例模型，其构造方法仅会调用一次:

@frameworks/base/services/sensorservice/SensorDevice.cpp

SensorDevice::SensorDevice()
    :  mSensorDevice(0), mSensorModule(0)
{
        // 终于看到hw_get_module了，幸福，高兴，开心，相见时难别亦难…
    status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
            (hw_module_t const**)&mSensorModule);
    LOGE_IF(err, "couldn‘t load %s module (%s)",
            SENSORS_HARDWARE_MODULE_ID, strerror(-err));
    if (mSensorModule) {
            //打开module设备，返回module设备的操作接口，保存在mSensorDevice中
        err = sensors_open(&mSensorModule->common, &mSensorDevice);
        LOGE_IF(err, "couldn‘t open device for module %s (%s)",
                SENSORS_HARDWARE_MODULE_ID, strerror(-err));
        if (mSensorDevice) {
            sensor_t const* list;
              // 调用module设备的get_sensors_list接口
            ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);
            mActivationCount.setCapacity(count);
            Info model;
            for (size_t i=0 ; i<size_t(count) ; i++) {
                mActivationCount.add(list[i].handle, model);
                mSensorDevice->activate(mSensorDevice, list[i].handle, 0);
            }
        }
    }
}

在SensorDevice构造方法里调用HAL架构的hw_get_module来获得Sensor设备模块，之后调用sensors_open这个工具函数，打开Sensor设备模块（调用其methods->open函数指针），返回Sensor设备的操作接口（这些接口在HAL层实现），保存在mSensorDevice中，调用Sensor模块的get_sensors_list方法获得传感器列表，然后依次激活这些设备并且添加到mActivationCount设备信息向量中。

Sensor HAL模块代码及打开模块工具函数sensors_open：

@hardware/libhardware/include/hardware/sensors.h

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);
};
……
static inline int sensors_open(const struct hw_module_t* module,
        struct sensors_poll_device_t** device) {
    return module->methods->open(module,
            SENSORS_HARDWARE_POLL, (struct hw_device_t**)device);
}

SensorDevice其它几个方法比较简单：

ssize_t SensorDevice::getSensorList(sensor_t const** list) {
    if (!mSensorModule) return NO_INIT;
       // 直接调用模块的get_sensors_list方法获得Sensor列表
    ssize_t count = mSensorModule->get_sensors_list(mSensorModule, list);
    return count;
}

ssize_t SensorDevice::poll(sensors_event_t* buffer, size_t count) {
    if (!mSensorDevice) return NO_INIT;
    ssize_t c;
    do {
           // 调用Sensor设备的poll操作接口，该接口实现在HAL层
        c = mSensorDevice->poll(mSensorDevice, buffer, count);
    } while (c == -EINTR);
    return c;
}

status_t SensorDevice::activate(void* ident, int handle, int enabled)
{
    if (!mSensorDevice) return NO_INIT;
    status_t err(NO_ERROR);
    bool actuateHardware = false;

    Info& info( mActivationCount.editValueFor(handle) );

    LOGD_IF(DEBUG_CONNECTIONS,
            "SensorDevice::activate: ident=%p, handle=0x%08x, enabled=%d, count=%d",
            ident, handle, enabled, info.rates.size());

    if (enabled) {
        Mutex::Autolock _l(mLock);
        LOGD_IF(DEBUG_CONNECTIONS, "... index=%ld",
                info.rates.indexOfKey(ident));
           // 设置设备为默认延迟级别
        if (info.rates.indexOfKey(ident) < 0) {
            info.rates.add(ident, DEFAULT_EVENTS_PERIOD);
            if (info.rates.size() == 1) {
                actuateHardware = true;
            }
        } else {
            // sensor was already activated for this ident
        }
    } else {
        Mutex::Autolock _l(mLock);
        LOGD_IF(DEBUG_CONNECTIONS, "... index=%ld",
                info.rates.indexOfKey(ident));

        ssize_t idx = info.rates.removeItem(ident);
        if (idx >= 0) {
            if (info.rates.size() == 0) {
                actuateHardware = true;
            }
        } else {
            // sensor wasn‘t enabled for this ident
        }
    }

    if (actuateHardware) {
        LOGD_IF(DEBUG_CONNECTIONS, "\t>>> actuating h/w");
          // 调用Sensor设备activate操作接口，其实现在HAL层
        err = mSensorDevice->activate(mSensorDevice, handle, enabled);
        if (enabled) {
            LOGE_IF(err, "Error activating sensor %d (%s)", handle, strerror(-err));
            if (err == 0) {
                 // 在电池服务中使能Sensor电源
                BatteryService::getInstance().enableSensor(handle);
            }
        } else {
            if (err == 0) {
                 // 在电池服务中关闭Sensor电源
                BatteryService::getInstance().disableSensor(handle);
            }
        }
    }

    { // scope for the lock
        Mutex::Autolock _l(mLock);
        nsecs_t ns = info.selectDelay();
          // 设置延迟值
        mSensorDevice->setDelay(mSensorDevice, handle, ns);
    }

    return err;
}