Sensor -- HAL 分析

1、Android sensor架构


Android4.0系统内置对传感器的支持达13种,它们分别是:加速度传感器gsensor(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:

各部分之间架构图如下:

2、Sensor HAL层接口

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

对传感器类型的定义:

传感器模块的定义结构体如下:

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。


对任意一个sensor设备 都会有一个 sensor_t 结构体,其定义如下:


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];
};


每个传感器的数据由sensors_event_t结构体表示,定义如下:

其中,sensor为传感器的标志符,而不同的传感器则采用union方式来表示,sensors_vec_t结构体用来表示不同传感器的数据,sensors_vec_t定义如下:

Sensor设备结构体sensors_poll_device_t,对标准硬件设备hw_device_t 结构体的扩展,主要完成 读取 底层数据,并将数据存储在struct sensors_poll_device_t 结构体中,poll函数用来获取底层数据,调用时将被阻塞 定义如下:


struct sensors_poll_device_t {


    struct hw_device_t common;


    /** Activate/deactivate one sensor.
     *
     * @param handle is the handle of the sensor to change.
     * @param enabled set to 1 to enable, or 0 to disable the sensor.
     *
     * @return 0 on success, negative errno code otherwise
     */
    int (*activate)(struct sensors_poll_device_t *dev,
            int handle, int enabled);

    /**
     * Set the delay between sensor events in nanoseconds for a given sensor.
     *
     * If the requested value is less than sensor_t::minDelay, then it's
     * silently clamped to sensor_t::minDelay unless sensor_t::minDelay is
     * 0, in which case it is clamped to >= 1ms.
     *
     * @return 0 if successful, < 0 on error
     */
    int (*setDelay)(struct sensors_poll_device_t *dev,
            int handle, int64_t ns);

    /**
     * Returns an array of sensor data.
     * This function must block until events are available.
     *
     * @return the number of events read on success, or -errno in case of an error.
     * This function should never return 0 (no event).
     *
     */
    int (*poll)(struct sensors_poll_device_t *dev,
            sensors_event_t* data, int count);
};


控制设备打开/关闭结构体定义如下:

3、Sensor HAL实现(以LM75温度传感器为例子)

(1)打开设备流程图

(2)实现代码分析

在代码中含有两个传感器ADC电位器和LM75温度传感器,所以在sensor.c中,首先需要 定义 传感器数组 device_sensor_list[],其实就是初始化 struct sensor_t 结构体,初始化如下:

定义open_sensors 函数,来打开Sensor模块,代码如下:

在这个方法中,首先需要为 hw_device_t 分配内存空间,并对其 初始化 为 0,设置重要方法的实现。

control_open_data_source()打开传感器并使能设备:

调用sensor__data_poll方法读取数据:

/*轮询读取数据*/
        static int sensors__data_poll(struct sensors_data_context_t *dev, sensors_data_t * values)
        {
            int n;
            int mag;
            float temp;
            char buf[10];
            while (1) {
            if(count % 3 == 2) // 读取ADC值
            {
                if( read(dev->event_fd[0], &mag, sizeof(mag)) < 0)
                {
                   LOGE("read adc error");
                }else{
                dev->sensors[ID_MAGNETIC_FIELD].magnetic.v[0] =(float)mag;
                LOGE("read adc %f\n",(float)mag);
                *values = dev->sensors[ID_MAGNETIC_FIELD];
                values->sensor = ID_MAGNETIC_FIELD;
                count++;
                }
                usleep(500000);
                return ID_MAGNETIC_FIELD;
                }
                else if(count%3 == 1) //读取温度传感器值
                 {
                memset(buf, 0 ,sizeof(buf));
                if((n = read(dev->event_fd[1], buf, 10)) < 0)
                {
                    LOGE("read temp error");
                    }else{
                    buf[n - 1] = '\0';
                    temp =(float) (atoi(buf) / 1000);
                    dev->sensors[ID_TEMPERATURE].temperature = temp;
                    LOGE("read temp %f\n",temp);
                    *values = dev->sensors[ID_TEMPERATURE];
                    values->sensor = ID_TEMPERATURE;
                    count++;
                }
                    close(dev->event_fd[1]);
                    dev->event_fd[1]= open("/sys/bus/i2c/devices/0-0048/temp1_input", O_RDONLY);
                    usleep(500000);
                    return ID_TEMPERATURE;
               }
               else if(count%3 == 0) //读取方向传感器模拟值
                 {
                    LOGI("read orientation\n");
                    /* fill up data of orientation */
                    dev->sensors[ID_ORIENTATION].orientation.azimuth = x + 5;
                    dev->sensors[ID_ORIENTATION].orientation.pitch = y + 5;
                    dev->sensors[ID_ORIENTATION].orientation.roll = z + 5;
                    *values = dev->sensors[ID_ORIENTATION];
                    values->sensor = ID_ORIENTATION;
                    count++;
                    x += 0.0001; y += 0.0001; z += 0.0001;
                    usleep (500000);
                    return ID_ORIENTATION;
              }
            }

        }






posted @ 2013-06-10 23:19  点点爱梦  阅读(460)  评论(0编辑  收藏  举报