前言

高通的hal层其实分2种，一种是直接从kernel这边报数据上来，由sensorhal层来监听，另外一种是走ADSP的模式，HAL层通过qmi的形式进行监听的。

hal层简介

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

为了理清HAL层的sensor我们必须要理解几个概念，分别是sensor_type,sensor_module,sensor_t,sensor_

/* * SENSOR_TYPE_ACCELEROMETER * reporting-mode: continuous * *  All values are in SI units (m/s^2) and measure the acceleration of the *  device minus the force of gravity. * *  Implement the non-wake-up version of this sensor and implement the wake-up *  version if the system possesses a wake up fifo. */#define SENSOR_TYPE_ACCELEROMETER                    (1)#define SENSOR_STRING_TYPE_ACCELEROMETER             "android.sensor.accelerometer"

从上面可以看到此文件定义了sensor的type以及string type.

/** * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM * and the fields of this data structure must begin with hw_module_t * followed by module specific information. */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);};

该接口的定义实际上是对标准的硬件模块hw_module_t的一个扩展，增加了一个get_sensors_list函数，用于获取传感器的列表，以及set_operation_mode 设置成相关的mode

struct sensor_t {    /* Name of this sensor.     * All sensors of the same "type" must have a different "name".     */    const char*     name; //传感器名字    /* 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; //版本    /* handle that identifies this sensors. This handle is used to reference     * this sensor throughout the HAL API.     */    int             handle; //传感器的handle句柄    /* this sensor's type. */    int             type;  //传感器类型    /* maximum range of this sensor's value in SI units */    float           maxRange; //最大范围    /* smallest difference between two values reported by this sensor */    float           resolution; //解析度    /* 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. Set to corresponding     * SENSOR_STRING_TYPE_*.     * When defining an OEM specific sensor or sensor manufacturer specific     * sensor, use your reserve domain name as a prefix.     * ex: com.google.glass.onheaddetector     * For sensors of known type, the android framework might overwrite this     * string automatically.     */    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];};

可以看出现在的android 7.1.1已经有了一些变化了，
从前reserved[8]现在已经只有reserved[2]了.

主要的方面新增方面：
* fifoReservedEventCount
* fifoMaxEventCount
* stringType
* requiredPermission
* maxDelay
* flags

为了不误导大家就让大家直接读code里面的注释，毕竟google介绍的还是很详尽的。

 * 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 {        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;            /* uncalibrated gyroscope values are in rad/s */            uncalibrated_event_t uncalibrated_gyro;            /* uncalibrated magnetometer values are in micro-Teslas */            uncalibrated_event_t uncalibrated_magnetic;            /* heart rate data containing value in bpm and status */            heart_rate_event_t heart_rate;            /* this is a special event. see SENSOR_TYPE_META_DATA above.             * sensors_meta_data_event_t events are all reported with a type of             * SENSOR_TYPE_META_DATA. The handle is ignored and must be zero.             */            meta_data_event_t meta_data;            /* dynamic sensor meta event. See SENSOR_TYPE_DYNAMIC_SENSOR_META type for details */            dynamic_sensor_meta_event_t dynamic_sensor_meta;            /*             * special additional sensor information frame, see             * SENSOR_TYPE_ADDITIONAL_INFO for details.             */            additional_info_event_t additional_info;        };        union {            uint64_t        data[8];            /* step-counter */            uint64_t        step_counter;        } u64;    };    /* Reserved flags for internal use. Set to zero. */    uint32_t flags;    uint32_t reserved1[3];} sensors_event_t;

不过目前就我工作中的话尚未使用到这边，一边来讲厂商更愿意的是自己来定制HAL层。

定制hal层

首先来看一个Android.mk来分析厂商是咋么定制的

LOCAL_PATH := $(call my-dir)include $(CLEAR_VARS)LOCAL_MODULE := sensors.PALS.msm8953######################## For 64/32 but build#ifeq ($(TARGET_ARCH), arm64)LOCAL_MODULE_PATH_64 := $(TARGET_OUT_SHARED_LIBRARIES)elseLOCAL_MODULE_PATH := $(TARGET_OUT_SHARED_LIBRARIES)endif#######################LOCAL_PRELINK_MODULE := falseLOCAL_MODULE_TAGS := optionalLOCAL_MODULE_OWNER := ALEXLOCAL_CFLAGS := -DLOG_TAG=\"Sensors\"## ANDROID version checkMAJOR_VERSION :=$(shell echo $(PLATFORM_VERSION) | cut -f1 -d.)MINOR_VERSION :=$(shell echo $(PLATFORM_VERSION) | cut -f2 -d.)VERSION_JB :=$(shell test $(MAJOR_VERSION) -gt 4 -o $(MAJOR_VERSION) -eq 4 -a $(MINOR_VERSION) -gt 0 && echo true)$(info MAJOR_VERSION=$(MAJOR_VERSION))$(info MINOR_VERSION=$(MINOR_VERSION))#ANDROID version check ENDifeq ($(VERSION_JB),true)LOCAL_CFLAGS += -DANDROID_JELLYBEANendif# c fileLOCAL_SRC_FILES := SensorBase.cppLOCAL_SRC_FILES += InputEventReader.cppLOCAL_SRC_FILES += sensors_mpl.cppLOCAL_SRC_FILES += LightSensor.cppLOCAL_SRC_FILES += ProximitySensor.cpp# share libLOCAL_SHARED_LIBRARIES := libcutilsLOCAL_SHARED_LIBRARIES += libutilsLOCAL_SHARED_LIBRARIES += libdlLOCAL_SHARED_LIBRARIES += liblog#LOCAL_SHARED_LIBRARIES += libmlliteinclude $(BUILD_SHARED_LIBRARY)

从上面我们可以看出将会生意一个名为libsensor.PALS.msm8953.so的档做为库，具体系统是咋么将这个so档起作用的，后面我们再分析，先分析一下HAL层一些做法。

Android Sensor详解（8）sensor hal层分析第一篇

前言

hal层简介

定制hal层

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