Android(安卓)Sensor HAL层分析

Android sensor架构

Android4系统内置对传感器的支持有很多种，它们分别是：加速度传感器 (accelerometer)、磁力传感器(magnetic field)、方向传感器(orientation)、陀螺仪(gyroscope)、环境光照传感器(light)、压力传感器(pressure)、温度传感器(temperature)和距离传感器(proximity)等。

Android实现传感器系统包括以下几个部分：

类别	名称	代码
用户空间	Java 应用程序	用户实现
	Java framework 框架层	SensorManager.java SensorListener.java SensorEvent.java
	JNI层	com_android_server_SystemServer.cpp SensorService.cpp SensorDevice.cpp
	HAL层	Sensors.cpp Sensors.h (sensor厂商实现的各家HAL Accelerater.cpp Proximity.cpp Gyroscope.cpp )
内核空间	设备驱动程序	厂商实现
硬件	具体sensor IC	---------

各部分架构图：

JNI 层与HAL层接口

/frameworks/native/services/sensorservice/SensorDevice.cpp

/frameworks/native/services/sensorservice/SensorDevice.h

SensorDevcie类的定义如下（JNI层通过这个类的对象与HAL层通信，包括控制sensor，读取sensor数据等）：

class SensorDevice : public Singleton, public Dumpable {public:    ssize_t getSensorList(sensor_t const** list);    void handleDynamicSensorConnection(int handle, bool connected);    status_t initCheck() const;    int getHalDeviceVersion() const;    ssize_t poll(sensors_event_t* buffer, size_t count);    status_t activate(void* ident, int handle, int enabled);    status_t batch(void* ident, int handle, int flags, int64_t samplingPeriodNs,                   int64_t maxBatchReportLatencyNs);    // Call batch with timeout zero instead of calling setDelay() for newer devices.    status_t setDelay(void* ident, int handle, int64_t ns);    status_t flush(void* ident, int handle);    status_t setMode(uint32_t mode);    void disableAllSensors();    void enableAllSensors();    void autoDisable(void *ident, int handle);    status_t injectSensorData(const sensors_event_t *event);    // Dumpable    virtual std::string dump() const;private:    friend class Singleton;    sensors_poll_device_1_t* mSensorDevice;    struct sensors_module_t* mSensorModule;    static const nsecs_t MINIMUM_EVENTS_PERIOD =   1000000; // 1000 Hz    mutable Mutex mLock; // protect mActivationCount[].batchParams    // fixed-size array after construction    // Struct to store all the parameters(samplingPeriod, maxBatchReportLatency and flags) from    // batch call. For continous mode clients, maxBatchReportLatency is set to zero.    struct BatchParams {      // TODO: Get rid of flags parameter everywhere.      int flags;      nsecs_t batchDelay, batchTimeout;      BatchParams() : flags(0), batchDelay(0), batchTimeout(0) {}      BatchParams(int flag, nsecs_t delay, nsecs_t timeout): flags(flag), batchDelay(delay),          batchTimeout(timeout) { }      bool operator != (const BatchParams& other) {          return other.batchDelay != batchDelay || other.batchTimeout != batchTimeout ||                 other.flags != flags;      }    };  // Store batch parameters in the KeyedVector and the optimal batch_rate and timeout in    // bestBatchParams. For every batch() call corresponding params are stored in batchParams    // vector. A continuous mode request is batch(... timeout=0 ..) followed by activate(). A batch    // mode request is batch(... timeout > 0 ...) followed by activate().    // Info is a per-sensor data structure which contains the batch parameters for each client that    // has registered for this sensor.    struct Info {        BatchParams bestBatchParams;        // Key is the unique identifier(ident) for each client, value is the batch parameters        // requested by the client.        KeyedVector batchParams;        Info() : bestBatchParams(0, -1, -1) {}        // Sets batch parameters for this ident. Returns error if this ident is not already present        // in the KeyedVector above.        status_t setBatchParamsForIdent(void* ident, int flags, int64_t samplingPeriodNs,                                        int64_t maxBatchReportLatencyNs);        // Finds the optimal parameters for batching and stores them in bestBatchParams variable.        void selectBatchParams();        // Removes batchParams for an ident and re-computes bestBatchParams. Returns the index of        // the removed ident. If index >=0, ident is present and successfully removed.        ssize_t removeBatchParamsForIdent(void* ident);        int numActiveClients();    };    DefaultKeyedVector mActivationCount;    // Use this vector to determine which client is activated or deactivated.    SortedVector mDisabledClients;    SensorDevice();    bool isClientDisabled(void* ident);    bool isClientDisabledLocked(void* ident);};

SensorDevcie 构造函数定义如下：

SensorDevice::SensorDevice()    :  mSensorDevice(0),       mSensorModule(0) {    status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,            (hw_module_t const**)&mSensorModule);    ALOGE_IF(err, "couldn't load %s module (%s)",            SENSORS_HARDWARE_MODULE_ID, strerror(-err));    if (mSensorModule) {        err = sensors_open_1(&mSensorModule->common, &mSensorDevice);        ALOGE_IF(err, "couldn't open device for module %s (%s)",                SENSORS_HARDWARE_MODULE_ID, strerror(-err));        if (mSensorDevice) {            if (mSensorDevice->common.version == SENSORS_DEVICE_API_VERSION_1_1 ||                mSensorDevice->common.version == SENSORS_DEVICE_API_VERSION_1_2) {                ALOGE(">>>> WARNING <<< Upgrade sensor HAL to version 1_3");            }            sensor_t const* list;            ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);            mActivationCount.setCapacity(count);            Info model;            for (size_t i=0 ; iactivate(                        reinterpret_cast(mSensorDevice),                        list[i].handle, 0);            }        }    }}

SensorDevcie 构造函数主要完成四部分工作

1.获得HAL层的sensors_module_t 并保存在 SensorDevcie 的数据成员 mSensorMoudle中

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

HAL层的sensors_module_t定义如下（三星平台sensor HAL的实现）

struct sensors_module_t HAL_MODULE_INFO_SYM = {    .common = {        .tag = HARDWARE_MODULE_TAG,        .version_major = 1,        .version_minor = 0,        .id = SENSORS_HARDWARE_MODULE_ID,        .name = "EXYNOS SENSORS Module",        .author = "Samsung",        .methods = &sensors_module_methods,    },    .get_sensors_list = sensors__get_sensors_list,};

2.获得HAL层的sensors_poll_context_t并保存在SensorDevcie 的数据成员 mSensorDevice中

err = sensors_open_1(&mSensorModule->common, &mSensorDevice);

HAL层的sensors_poll_context_t的定义如下：（三星平台sensor HAL的实现）

struct sensors_poll_context_t {    struct sensors_poll_device_1 device;// must be first        sensors_poll_context_t();        ~sensors_poll_context_t();    int activate(int handle, int enabled);    int setDelay(int handle, int64_t ns);    int pollEvents(sensors_event_t* data, int count);    int batch(int handle, int flags, int64_t samplingPeriodNs, int64_t maxBatchReportLatencyNs);    int flush(int handle);private:    enum {        PROXIMITY,        LIGHT,        SENSOR_NUMS,    };int handleToDriver(int handle) const {    ALOGE("handleToDriver handle(%d)\n",handle);        switch (handle) {        case ID_PROXIMITY:             return PROXIMITY;        case ID_LIGHT:             return LIGHT;        default:                break;    }    return 0;}    SensorBase* mSensors[SENSOR_NUMS];    struct pollfd mPollFds[SENSOR_NUMS];};

如果获得sensors_poll_context_t 就可在上层通过它的成员函数控制所有的sensor。（HAL 层主要是实现这些成员函数函数）

    int activate(int handle, int enabled);  //使能对应sensor    int setDelay(int handle, int64_t ns);       int pollEvents(sensors_event_t* data, int count);  //读取sensor上报的数据    int batch(int handle, int flags, int64_t samplingPeriodNs, int64_t maxBatchReportLatencyNs);    int flush(int handle);

HAL层对sensors_poll_device_t的初始化：（三星平台sensor HAL的实现，dev 对应sensors_poll_device_t）

static int open_sensors(const struct hw_module_t* module, const char* name,        struct hw_device_t** device){    int status = -EINVAL;    ALOGD("%s: name: %s! debug\r\n", __func__, name);    dev = new sensors_poll_context_t();    memset(&dev->device, 0, sizeof(sensors_poll_device_1));    dev->device.common.tag = HARDWARE_DEVICE_TAG;    dev->device.common.version  = SENSORS_DEVICE_API_VERSION_1_1;    dev->device.common.module   = const_cast(module);    dev->device.batch           = poll__batch;    dev->device.flush           = poll__flush;    dev->device.common.close    = poll__close;    dev->device.activate        = poll__activate;    dev->device.setDelay        = poll__setDelay;    dev->device.poll            = poll__poll;    *device = &dev->device.common;  // device 保存在SensorDevcie 的数据成员 mSensorDevice中    status = 0;    return status;}

3.获得HAL层的sensor_list

ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);

HAL层的sensor_list定义如下：（三星平台sensor HAL的实现）

struct sensor_t sSensorList[] ={   {        .name       = "PROXIMITY",        .vendor     = "Samsung",        .version    = 1,        .handle     = ID_PROXIMITY,        .type       = SENSOR_TYPE_PROXIMITY,        .maxRange   = 1.00f,        .resolution = 1.00f,        .power      = 0.13f,        .reserved   = {}    },    {        .name       = "LIGHT",        .vendor     = "Samsung",        .version    = 1,        .handle     = ID_LIGHT,        .type       = SENSOR_TYPE_LIGHT,        .maxRange   = 10240.0f,        .resolution = 1.0f,        .power      = 0.13f,        .reserved   = {}    }};

4.最后一步是使用sensors_poll_context_t 的 activate方法对上面sensor列表的sensor进行激活

for (size_t i=0 ; iactivate(                        reinterpret_cast(mSensorDevice),                        list[i].handle, 0);            }//reinterpret_cast是C++里的强制类型转换符。

HAL层

hardware/libhardware/include/hardware/sensors.h

hardware/samsung_slsi/exynos7570/libsensors/Sensors.cpp（三星平台的实现）

sensors.h为我们提供了HAL层的接口，实现部分则在sensors.cpp完成。sensors.cpp定义了一个hw_module_methods_t类型的变量sensors_module_methods，并且指定open函数的实现为open_sensors函数。

static struct hw_module_methods_t sensors_module_methods = {    .open = open_sensors};

static int open_sensors(const struct hw_module_t* module, const char* name,        struct hw_device_t** device){    int status = -EINVAL;    ALOGD("%s: name: %s! debug\r\n", __func__, name);    dev = new sensors_poll_context_t();    memset(&dev->device, 0, sizeof(sensors_poll_device_1));    dev->device.common.tag = HARDWARE_DEVICE_TAG;    dev->device.common.version  = SENSORS_DEVICE_API_VERSION_1_1;    dev->device.common.module   = const_cast(module);    dev->device.batch           = poll__batch;    dev->device.flush           = poll__flush;    dev->device.common.close    = poll__close;    dev->device.activate        = poll__activate;    dev->device.setDelay        = poll__setDelay;    dev->device.poll            = poll__poll;    *device = &dev->device.common;    status = 0;    return status;}

HAL层主要实现下面几个函数（具体函数的实现岁平台不同有差异）

    dev->device.batch           = poll__batch;    dev->device.flush           = poll__flush;    dev->device.common.close    = poll__close;    dev->device.activate        = poll__activate;    dev->device.setDelay        = poll__setDelay;    dev->device.poll            = poll__poll;

Android sensor架构

JNI 层与HAL层接口

HAL层

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