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1, Android sensor framework
Android4.0 system built up on the sensor support 13 species, which are: an acceleration sensor (Accelerometer), a magnetic sensor (magnetic field), a direction sensor (Orientation), gyroscopes (Gyroscope), ambient light sensor (Light), a pressure sensors (pressure), temperature sensor (temperature) and a distance sensor (Proximity) and the like.
The sensor system implemented Android includes the following components:
Between the portions of the organization chart below:
2, Sensor HAL layer interface
Google Sensor provides a unified interface to HAL, different hardware manufacturers need to achieve and accomplish specific hardware abstraction layer based on this interface, Android in Sensor Interface Definition of HAL in: hardware / libhardware / include / hardware / sensors.h
Definition of the type of sensor:
Definition of the structure of the sensor module are as follows:
The definition of the interface is actually an extension of the standard hardware modules hw_module_t, get_sensors_list adds a function for list acquisition sensor.
Sensor_t has a structure of any one of the sensor device are defined as follows:
Data from each sensor is represented by sensors_event_t structures, defined as follows:
Wherein, sensor is a sensor identifier, different sensors are employed to represent the union embodiment, sensors_vec_t data structure used to represent different sensors, sensors_vec_t defined as follows:
Sensor device structure sensors_poll_device_t, hardware hw_device_t extended standard device structure, the main completion of reading the underlying data, and the data stored in struct sensors_poll_device_t structural body, poll function to retrieve the underlying data, the call will be blocked is defined as follows:
The control device opening / closing structure is defined as follows:
3, Sensor HAL implemented (LM75 temperature sensor in the example)
(1) Open the device flowchart
(2) implementation code analysis
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，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;
}
}
}