HillCrest Sensor HAL

目录

• 1. 抽象定义
  • 1.1 sensor type
• 1.2 sensor_t
  • 1.3 sensor_module_t
  • 1.4 sensors_poll_device_t
• 2. 抽象方法
  • 2.1 get_sensors_list
  • 2.2 open method
  • 2.3 activate、setDelay、poll
• 3. 框架流程
• 4. 问题分析

1. 抽象定义

Google为Sensor提供了统一的HAL接口，不同的硬件厂商需要根据该接口来实现并完成具体的硬件抽象层，Android中Sensor的HAL接口定义在：hardware/libhardware/include/hardware/sensors.h，

其中定义了几个数据类型：

• sensor_t - 包含传感器相关信息
• sensors_module_t - 传感器硬件模块类型
• sensors_event_t - 传感器事件
• sensors_poll_device_t - 传感器抽象设备类型

HAL实现必须完成下面的函数接口：

• get_sensors_list - 返回所有传感器的列表
• activate - 启动或停止传感器
• batch - 设置传感器的参数，如采样率和最大报告延迟
• setDelay - 仅用于 1.0 版本的 HAL，设置指定传感器的采样率
• flush - 刷写指定传感器的 FIFO 并在完成后报告刷写完成事件
• poll - 返回可用的传感器事件

1.1 sensor type

sensor type的定义如下：

[sensors-base.h]
enum {
    SENSOR_TYPE_META_DATA = 0,
    SENSOR_TYPE_ACCELEROMETER = 1,
    SENSOR_TYPE_MAGNETIC_FIELD = 2,
    SENSOR_TYPE_ORIENTATION = 3,
    SENSOR_TYPE_GYROSCOPE = 4,
    SENSOR_TYPE_LIGHT = 5,
    SENSOR_TYPE_PRESSURE = 6,
    SENSOR_TYPE_TEMPERATURE = 7,
    SENSOR_TYPE_PROXIMITY = 8,
    SENSOR_TYPE_GRAVITY = 9,
    ...
}

#define SENSOR_STRING_TYPE_ACCELEROMETER                "android.sensor.accelerometer"
#define SENSOR_STRING_TYPE_MAGNETIC_FIELD               "android.sensor.magnetic_field"
#define SENSOR_STRING_TYPE_ORIENTATION                  "android.sensor.orientation"
#define SENSOR_STRING_TYPE_GYROSCOPE                    "android.sensor.gyroscope"
#define SENSOR_STRING_TYPE_LIGHT                        "android.sensor.light"
#define SENSOR_STRING_TYPE_PRESSURE                     "android.sensor.pressure"
#define SENSOR_STRING_TYPE_TEMPERATURE                  "android.sensor.temperature"
#define SENSOR_STRING_TYPE_PROXIMITY                    "android.sensor.proximity"

1.2 sensor_t

sensor_t 的定义如下

[sensors.h]
struct sensor_t {

    /* Name of this sensor.
     * All sensors of the same "type" must have a different "name".
     */
    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 reference
     * this sensor throughout the HAL API.
     */
    int             handle;

    /* this sensor's type. */
    int             type;	//sensor type

    /* maximum 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;

    /* this value depends on the reporting mode:
     *
     *   continuous: minimum sample period allowed in microseconds
     *   on-change : 0
     *   one-shot  :-1
     *   special   : 0, unless otherwise noted
     */
    int32_t         minDelay;

    /* number of events reserved for this sensor in the batch mode FIFO.
     * If there is a dedicated FIFO for this sensor, then this is the
     * size of this FIFO. If the FIFO is shared with other sensors,
     * this is the size reserved for that sensor and it can be zero.
     */
    uint32_t        fifoReservedEventCount;

    /* maximum number of events of this sensor that could be batched.
     * This is especially relevant when the FIFO is shared between
     * several sensors; this value is then set to the size of that FIFO.
     */
    uint32_t        fifoMaxEventCount;

    /* type of this sensor as a string.
     *
     * If type is OEM specific or sensor manufacturer specific type
     * (>=SENSOR_TYPE_DEVICE_PRIVATE_BASE), this string must be defined with reserved domain of
     * vendor/OEM as a prefix, e.g. com.google.glass.onheaddetector
     *
     * For sensors of Android defined types, Android framework will override this value. It is ok to
     * leave it pointing to an empty string.
     */
    const char*    stringType;

    /* permission required to see this sensor, register to it and receive data.
     * Set to "" if no permission is required. Some sensor types like the
     * heart rate monitor have a mandatory require_permission.
     * For sensors that always require a specific permission, like the heart
     * rate monitor, the android framework might overwrite this string
     * automatically.
     */
    const char*    requiredPermission;

    /* This value is defined only for continuous mode and on-change sensors. It is the delay between
     * two sensor events corresponding to the lowest frequency that this sensor supports. When lower
     * frequencies are requested through batch()/setDelay() the events will be generated at this
     * frequency instead. It can be used by the framework or applications to estimate when the batch
     * FIFO may be full.
     *
     * NOTE: 1) period_ns is in nanoseconds where as maxDelay/minDelay are in microseconds.
     *              continuous, on-change: maximum sampling period allowed in microseconds.
     *              one-shot, special : 0
     *   2) maxDelay should always fit within a 32 bit signed integer. It is declared as 64 bit
     *      on 64 bit architectures only for binary compatibility reasons.
     * Availability: SENSORS_DEVICE_API_VERSION_1_3
     */
    #ifdef __LP64__
       int64_t maxDelay;
    #else
       int32_t maxDelay;
    #endif

    /* Flags for sensor. See SENSOR_FLAG_* above. Only the least significant 32 bits are used here.
     * It is declared as 64 bit on 64 bit architectures only for binary compatibility reasons.
     * Availability: SENSORS_DEVICE_API_VERSION_1_3
     */
    #ifdef __LP64__
       uint64_t flags;
    #else
       uint32_t flags;
    #endif

    /* reserved fields, must be zero */
    void*           reserved[2];
};

1.3 sensor_module_t

该结构体实际上是对标准硬件模块hw_module_t的一个扩展，增加一个get_sensor_list函数，用于获取传感器的列表，以及set_operation_mode设置为相关的mode；

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);

    /**
     *  Place the module in a specific mode. The following modes are defined
     *
     *  0 - Normal operation. Default state of the module.
     *  1 - Loopback mode. Data is injected for the supported
     *      sensors by the sensor service in this mode.
     * return 0 on success
     *         -EINVAL if requested mode is not supported
     *         -EPERM if operation is not allowed
     */
    int (*set_operation_mode)(unsigned int mode);
};

1.4 sensors_poll_device_t

sensors_poll_device_t 定义了以下方法

[sensors.h]
struct sensors_poll_device_t {
    struct hw_device_t common;
    int (*activate)(struct sensors_poll_device_t *dev,
            int sensor_handle, int enabled);
    int (*setDelay)(struct sensors_poll_device_t *dev,
            int sensor_handle, int64_t sampling_period_ns);
    int (*poll)(struct sensors_poll_device_t *dev,
            sensors_event_t* data, int count);
};

2. 抽象方法

2.1 get_sensors_list

sensors_module_t 是用于为传感器创建 Android 硬件模块的类型。HAL 的实现必须定义一个该类型的对象 HAL_MODULE_INFO_SYM，以提供 get_sensors_list 函数。

[HAL.cpp]
struct sensors_module_t HAL_MODULE_INFO_SYM = {
	.common = {
		.tag = HARDWARE_MODULE_TAG,
#ifdef SENSORS_MODULE_API_VERSION_0_1
		.module_api_version = SENSORS_MODULE_API_VERSION_0_1,
#else
		.module_api_version = 0,
#endif
		.hal_api_version = 0,
		.id = SENSORS_HARDWARE_MODULE_ID,
		.name = "Freespace SensorHub Sensor Module",
		.author = "Hillcrest Labs, Inc.",
		.methods = &sensors_module_methods,
		.dso = 0,
		.reserved = {},
	},
	.get_sensors_list = get_sensors_list
};

get_sensors_list 提供由 HAL 实现的传感器列表，该函数返回列表中的传感器数量。
调用单例模式实例化，然后调用对应方法获取传感器列表，返回对应的 sensor_t 结构体数组指针。

static int get_sensors_list(struct sensors_module_t* module,
		struct sensor_t const** list) {

	if (getContext()) {
		return getContext()->getSensorList(list);
	}

	return 0;
}


static Context * getContext() {
	if (context_) {
		return context_;
	}

	if (!HAL_ENABLED) {
		return NULL;
	}

	context_ = new Context();
#ifdef ENABLE_SOURCE_OBSERVER
	if (OBS_ENABLED) {
		hubServer_  = new HubServer(*context_, true);
	}
#endif
	return context_;
}

2.2 open method

打开 sensor 的实例化对象， 并填充 hw_device_t

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

struct hcrest_sensors_device_t {
#ifdef SENSORS_DEVICE_API_VERSION_1_1
	struct sensors_poll_device_1 base; // must be first
#else
	struct sensors_poll_device_t base; // must be first
#endif
	unsigned int magic;
	void * context;
};

static hcrest_sensors_device_t hwdevice_;

static bool open_ = false;

static int open_sensors(const struct hw_module_t* module, const char* name,
		struct hw_device_t** device) {

	LOGI("Freespace SensorHub HAL open");
	LOGD("   open from: %s", name);
	LOGI("   version:   " FS_SENSORHUB_HAL_VERSION);

	if (open_) {
		LOGE("Already open, refusing open_sensors");
		return -EBUSY;
	}

	int rc;
	*device = NULL;
	Context * context = getContext();

	if (context) {
		hwdevice_.base.common.tag     = HARDWARE_DEVICE_TAG;
#if defined(SENSORS_DEVICE_API_VERSION_1_3)
		hwdevice_.base.common.version = SENSORS_DEVICE_API_VERSION_1_3;
#elif defined(SENSORS_DEVICE_API_VERSION_1_2)
		hwdevice_.base.common.version = SENSORS_DEVICE_API_VERSION_1_2;
#elif defined(SENSORS_DEVICE_API_VERSION_1_1)
		hwdevice_.base.common.version = SENSORS_DEVICE_API_VERSION_1_1;
#elif defined(SENSORS_DEVICE_API_VERSION_1_0)
		hwdevice_.base.common.version = SENSORS_DEVICE_API_VERSION_1_0;
#else
		hwdevice_.base.common.version = 0;
#endif
		hwdevice_.base.common.module  = const_cast<hw_module_t*>(module);

		hwdevice_.base.common.close   = ctx_close;
		hwdevice_.base.activate       = ctx_activate;
		hwdevice_.base.setDelay       = ctx_setDelay;
		hwdevice_.base.poll           = ctx_poll;

#ifdef SENSORS_DEVICE_API_VERSION_1_1
		hwdevice_.base.batch          = ctx_batch;
		hwdevice_.base.flush          = ctx_flush;
#endif
		hwdevice_.magic               = HCREST_MAGIC;
		hwdevice_.context             = context;

		rc =  context->open();

#ifdef ENABLE_SOURCE_OBSERVER
		if (rc == 0 && OBS_ENABLED) {
			LOGI("Initializing source server");
			if ((rc = hubServer_->init())) {
				LOGE("Failed initializing server");
				freeContext();
			}
		}
#endif
		if (!rc) {
			*device = &hwdevice_.base.common;
		}
	} else {
		// Dummy context
		*device = NULL;
		rc = 0;
		LOGD(">>> Dummy Sensors <<<");
	}

	LOGD("Freespace SensorHub HAL open = %s, device=%p ", rc ? strerror(-rc) : "Success", *device);
	return rc;
}

先看下 context->open() , 打开挂在 SensorHub 上的所有 sensor，并设置 hcrest_sensors_device_t

[Context.cpp]
int Context::open() {
	int rc;
	quit_ = false;

#ifdef CONTROL_INTERFACE
	rc = ctrlIface_.init(this);
	if (rc < 0) {
		return rc;
	}
#endif

	if ((rc = hub_.probe())) {
		return rc;
	}

#ifdef EXTENSION_LIB
	if ((rc = external_sensors_init(*this))) {
		LOGW("Error from external_sensors_init() = %d; %s", rc, strerror(rc));
	}
#endif

	return 0;
}

SensorHub::probe() 继续调用基类的 probe， SensorHubDevice::probe 到这里浅尝辄止。

[SensorHub.cpp]
int SensorHub::probe() {
	AutoLock _l(configLock_);
	AutoLock _ll(pollLock_);

	int rc = SensorHubDevice::probe();
	if (rc < 0) {
		return rc;
	}

	rc = frsDirector_.probe();
	if (rc < 0) {
		return rc;
	}

	ctx_.addFd(normal_.getFd(), POLLIN | POLLHUP | POLLERR, this);

	if ((rc = initSensorsLocked())) {
		return rc;
	}

	// switch to non-blocking
	open_ = true;
	return 0;
}

2.3 activate、setDelay、poll

[HAL.cpp]
static int ctx_activate(struct sensors_poll_device_t *dev, int handle, int enabled) {
	return toContext(dev)->activate(handle, enabled);
}

static int ctx_setDelay(struct sensors_poll_device_t *dev, int handle, int64_t ns) {
	return toContext(dev)->setDelay(handle, ns);
}

static int ctx_poll(struct sensors_poll_device_t *dev, sensors_event_t* data, int count) {
	return toContext(dev)->pollEvents(data, count);
}

#ifdef SENSORS_DEVICE_API_VERSION_1_1
static int ctx_batch(struct sensors_poll_device_1 *dev, int sensor_handle, int flags,
     int64_t sampling_period_ns,
     int64_t max_report_latency_ns) {
	return toContext(dev)->batch(sensor_handle, flags, sampling_period_ns, max_report_latency_ns);
}

static int ctx_flush(struct sensors_poll_device_1 *dev, int sensor_handle) {
 	return toContext(dev)->flush(sensor_handle);
}
#endif

• activate 激活或禁用传感器

int (*activate)(struct sensors_poll_device_t *dev, int sensor_handle, int enabled);

如果 enabled 为 1 且传感器已激活，则该函数是空操作且操作成功。
如果 enabled 为 0 且传感器已禁用，则该函数是空操作且操作成功。
如果操作成功了，则该函数返回 0；否则返回表示错误的负数。

• poll 机制来轮询读取数据

int (*poll)(struct sensors_poll_device_t *dev, sensors_event_t* data, int count);

• batch 设置传感器的参数（包括采样率和最大报告延迟）

int (*batch)( struct sensors_poll_device_1* dev, int sensor_handle, int flags, int64_t sampling_period_ns, int64_t max_report_latency_ns);

• flush 将刷新完成事件添加到指定传感器的硬件 FIFO末尾并刷新 FIFO

int (*flush)(struct sensors_poll_device_t* dev, int sensor_handle);

Sensor HAL的简单流程可以按照下面来理解：

当设备启动时，调用 get_sensors_list。

当传感器激活时，则先使用请求的参数调用 batch 函数，然后调用 activate(..., enable=1)。

当激活状态下的传感器的请求特性发生变化时，会调用 batch 函数。

可以随时调用 flush，甚至在未激活的传感器上也可以调用（在这种情况下，该函数必须返回 -EINVAL）

当传感器禁用时，将调用 activate(..., enable=0)。

在进行上述调用的同时，会反复调用 poll 函数来请求数据。甚至在没有传感器激活的情况下，也可以调用 poll。

3. 框架流程

当前方案AP并未直接对接 SensorHUB，而是将 SensorHUB 挂载在一颗 MCU 上，AP与MCU通过USB相连接，进行数据传输。

基本框架如下图所示：

• IMU App
  App 通过正常的 SDK 接口访问 Sensor 服务，获取 Sensor 数据。

• Framewrok Java
  SensorManager 提供了 Java 层 Sensor 的接口，并通过 JNI 和 Native SensorManager 通信。
  代码位于 frameworks/base/core/java/android/hardware/SensorManage.java

• Framework JNI
  提供机制，供 SensorManager 和 Native SensorManager 通信。
  代码位于 frameworks/base/core/jni/android_hardware_SensorManager.cpp

• Native Service & Libs
  SensorManager 属于 NativeLibs，为 JNI 提供接口，获取 SensorService 的服务，从而获取 SensorEvent；
  代码位于 frameworks/native/libs/sensor/SensorManager.cpp
  SensorService 属于 NativeService，向 SensorManager 注册服务，和 Sensor HAL 进行交互，控制 sensor 和获取 SensorEvent。
  代码位于 frameworks/native/services/sensorservice/SensorService.cpp

• HAL
  SensorHub HAL，向上为 Native SensorService 提供接口，向下和 Driver 进行交互。

• Driver
  创建虚拟设备节点，并提供接口供 HAL 层获取 SensorEvent 和控制 Sensor。

4. 问题分析

问题现象：
IMU sensordump App 无法获取 Accelerometer Sensor 数据

初步分析：
通过 dumpsys sensorservice 获取相关信息，发现 Client 0 中 Accelerometer 的状态是 First flush pending， 并不是 active 的状态。

2 active connections
Connection Number: 0
	Operating Mode: NORMAL
	 org.cvpcs.android.sensordump.ASensor | WakeLockRefCount 0 | uid 10056 | cache size 0 | max cache size 984
	 Rokid Glasses Accelerometer 0x00000001 | status: First flush pending | pending flush events 0
	 events recvd: 0 | sent 0 | cache 0 | dropped 0 | total_acks_needed 0 | total_acks_recvd 0
Connection Number: 1
	Operating Mode: NORMAL
	 com.android.server.policy.WindowOrientationListener | WakeLockRefCount 0 | uid 1000 | cache size 0 | max cache size 984
	 Rokid Glasses Accelerometer 0x00000001 | status: active | pending flush events 0
	 events recvd: 3976 | sent 3971 | cache 5 | dropped 0 | total_acks_needed 0 | total_acks_recvd 0

根据 log 定位 sensorservice 代码的位置，确定 mFirstFlushPending 标志被设置为 true

[SensorEventConnection.cpp]
void SensorService::SensorEventConnection::dump(String8& result) {
    Mutex::Autolock _l(mConnectionLock);
    result.appendFormat("	Operating Mode: %s
",mDataInjectionMode ? "DATA_INJECTION" : "NORMAL");
    result.appendFormat("	 %s | WakeLockRefCount %d | uid %d | cache size %d | "
            "max cache size %d
", mPackageName.string(), mWakeLockRefCount, mUid, mCacheSize,
            mMaxCacheSize);
    for (size_t i = 0; i < mSensorInfo.size(); ++i) {
        const FlushInfo& flushInfo = mSensorInfo.valueAt(i);
        result.appendFormat("	 %s 0x%08x | status: %s | pending flush events %d 
",
                            mService->getSensorName(mSensorInfo.keyAt(i)).string(),
                            mSensorInfo.keyAt(i),
                            flushInfo.mFirstFlushPending ? "First flush pending" :
                                                           "active",
                            flushInfo.mPendingFlushEventsToSend);

这个标志在构造函数初始化列表中被初始化为 false，那么这个标志是在哪里被修改的呢？
SensorEventConnection 类提供了 setFirstFlushPending 方法去设置这个标志，

[SensorEventConnection.cpp]
void SensorService::SensorEventConnection::setFirstFlushPending(int32_t handle,
                                bool value) {
    Mutex::Autolock _l(mConnectionLock);
    ssize_t index = mSensorInfo.indexOfKey(handle);
    if (index >= 0) {
        FlushInfo& flushInfo = mSensorInfo.editValueAt(index);
        flushInfo.mFirstFlushPending = value;
    }
}

而这个方法在类 SensorService 的 enable 方法中被调用。

[SensorService.cpp]
status_t SensorService::enable(const sp<SensorEventConnection>& connection,
        int handle, nsecs_t samplingPeriodNs, nsecs_t maxBatchReportLatencyNs, int reservedFlags,
        const String16& opPackageName) {
    ...
    if (err == NO_ERROR &&
            sensor->getSensor().getReportingMode() == AREPORTING_MODE_CONTINUOUS &&
            rec->getNumConnections() > 1) {
        connection->setFirstFlushPending(handle, true);
        status_t err_flush = sensor->flush(connection.get(), handle);
        // Flush may return error if the underlying h/w sensor uses an older HAL.
        if (err_flush == NO_ERROR) {
            rec->addPendingFlushConnection(connection.get());
        } else {
            connection->setFirstFlushPending(handle, false);
        }
    }
    ...    
}   

参考前面的 Sensor HAL 的流程分析，对比 enable 方法中的流程，先执行 batch 设置采样时间等参数，然后调用 flush 刷新 FIFO，最后调用 activcate 激活传感器。

SensorService 继承于 Thread， 复写方法 threadLoop，不断的从 Sensor HAL 中读取数据

[SensorService.cpp]
bool SensorService::threadLoop() {
    ALOGD("nuSensorService thread starting...");

    // each virtual sensor could generate an event per "real" event, that's why we need to size
    // numEventMax much smaller than MAX_RECEIVE_BUFFER_EVENT_COUNT.  in practice, this is too
    // aggressive, but guaranteed to be enough.
    const size_t vcount = mSensors.getVirtualSensors().size();
    const size_t minBufferSize = SensorEventQueue::MAX_RECEIVE_BUFFER_EVENT_COUNT;
    const size_t numEventMax = minBufferSize / (1 + vcount);

    SensorDevice& device(SensorDevice::getInstance());

    const int halVersion = device.getHalDeviceVersion();
    do {
        ssize_t count = device.poll(mSensorEventBuffer, numEventMax);
        if (count < 0) {
            ALOGE("sensor poll failed (%s)", strerror(-count));
            break;
        }

        // Reset sensors_event_t.flags to zero for all events in the buffer.
        for (int i = 0; i < count; i++) {
             mSensorEventBuffer[i].flags = 0;
        }

在读取完数据后，它会向所有连接的 Client 发送 SensorEvents

[SensorService.cpp]
        // Send our events to clients. Check the state of wake lock for each client and release the
        // lock if none of the clients need it.
        bool needsWakeLock = false;
        size_t numConnections = activeConnections.size();
        for (size_t i=0 ; i < numConnections; ++i) {
            if (activeConnections[i] != 0) {
                activeConnections[i]->sendEvents(mSensorEventBuffer, count, mSensorEventScratch,
                        mMapFlushEventsToConnections);
                needsWakeLock |= activeConnections[i]->needsWakeLock();
                // If the connection has one-shot sensors, it may be cleaned up after first trigger.
                // Early check for one-shot sensors.
                if (activeConnections[i]->hasOneShotSensors()) {
                    cleanupAutoDisabledSensorLocked(activeConnections[i], mSensorEventBuffer,
                            count);
                }
            }
        }

在 SendEvents 的方法中，判断获取的数据流中类型是否存在 SENSOR_TYPE_META_DATA ，如果有且 flushInfo.mFirstFlushPending == true，设置该标志为 false，然后接收到的数据才能被送到 Client。

[SensorEventConnection.cpp]
status_t SensorService::SensorEventConnection::sendEvents(
        sensors_event_t const* buffer, size_t numEvents,
        sensors_event_t* scratch,
        wp<const SensorEventConnection> const * mapFlushEventsToConnections) {
    ...
    if (scratch) {
        size_t i=0;
        while (i<numEvents) {
            int32_t sensor_handle = buffer[i].sensor;
            if (buffer[i].type == SENSOR_TYPE_META_DATA) {
                ALOGD_IF(DEBUG_CONNECTIONS, "flush complete event sensor==%d ",
                        buffer[i].meta_data.sensor);
                // Setting sensor_handle to the correct sensor to ensure the sensor events per
                // connection are filtered correctly.  buffer[i].sensor is zero for meta_data
                // events.
                sensor_handle = buffer[i].meta_data.sensor;
            }

            ssize_t index = mSensorInfo.indexOfKey(sensor_handle);
            // Check if this connection has registered for this sensor. If not continue to the
            // next sensor_event.
            if (index < 0) {
                ++i;
                continue;
            }

            FlushInfo& flushInfo = mSensorInfo.editValueAt(index);
            // Check if there is a pending flush_complete event for this sensor on this connection.
            if (buffer[i].type == SENSOR_TYPE_META_DATA && flushInfo.mFirstFlushPending == true &&
                    mapFlushEventsToConnections[i] == this) {
                flushInfo.mFirstFlushPending = false;
                ALOGD_IF(DEBUG_CONNECTIONS, "First flush event for sensor==%d ",
                        buffer[i].meta_data.sensor);
                ++i;
                continue;
            }
        ...        
        }
        ...
    }
    ...
    // NOTE: ASensorEvent and sensors_event_t are the same type.
    ssize_t size = SensorEventQueue::write(mChannel,
                                    reinterpret_cast<ASensorEvent const*>(scratch), count);
    ...
}

到这里问题的原因基本可以定位了，结合 libsensors log 确定 SensorHUB HAL 没有上报 SENSOR_TYPE_META_DATA 类型的数据到 SensorService，导致数据无法发送到对应的 Client。

这里追查了代码，发现 SENSOR_TYPE_META_DATA 类型的数据的上报流程不能正常工作，因为 SensorHUB HAL 适配当前方案时，移除了部分代码。在修改了这部分流程后，顺利解决了这一问题。

2 active connections
Connection Number: 0
	Operating Mode: NORMAL
	 org.cvpcs.android.sensordump.ASensor | WakeLockRefCount 0 | uid 10056 | cache size 0 | max cache size 984
	 Rokid Glasses Accelerometer 0x00000001 | status: active | pending flush events 0
	 events recvd: 6168 | sent 4353 | cache 1815 | dropped 0 | total_acks_needed 0 | total_acks_recvd 0
Connection Number: 1
	Operating Mode: NORMAL
	 com.android.server.policy.WindowOrientationListener | WakeLockRefCount 0 | uid 1000 | cache size 0 | max cache size 984
	 Rokid Glasses Accelerometer 0x00000001 | status: active | pending flush events 0
	 events recvd: 589106 | sent 588481 | cache 625 | dropped 0 | total_acks_needed 0 | total_acks_recvd 0
0 direct connections