gsensor架构和原理分析 .
本文主要描述了在android2.3平台G-sensor相关软硬件的体系架构和实现原理，按照Applications、Framework、HAL、Driver和Hardware五大层次分别介绍。
1.系统架构 (Architecture)
1.1 Android体系架构图
1.2 Sensor子系统架构图
・ Application Framework
Sensor应用程序通过Sensor应用框架来获取sensor数据，应用框架层的Sensor Manager通过JNI与C++层进行通信。
・ Sensor Libraries
Sensor中间层主要由Sensor Manager、Sensor service和Sensor硬件抽象层组成。
・ Input Subsystem
通用的Linux输入框架专为与键盘、鼠标和触摸屏等输入设备而设计，并定义了一套标准事件集合。Sensor输入子系统采用采用了通用的Linux输入框架，它通过/sys/class/input节点和用户空间进行交互。
・ Event Dev
Evdev提供了一种访问/dev/input/eventX输入设备事件的通用方法。
・ AccelerometerDriver
此驱动通过SIRQ和I2C总线与MMA7660模组进行通信。SIRQ用来产生传感器事件中断。
2 应用 (Applications)
2.1 应用开发五步曲
（1） 获取传感器管理器对象；
mSensorManager =(SensorManager) getSystemService(SENSOR_SERVICE);
（2） 获取传感器对象；
mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
（3） 定义事件监听器；
mEventListener =new SensorEventListener() {
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@Override
publicvoid onSensorChanged(SensorEvent event) {
float[] values = event.values;
mTextView.setText("Accelerometer:" + values[0] +", "
+ values[1] +", " + values[2]);
}
@Override
publicvoidonAccuracyChanged(Sensor sensor,int accuracy) {
}
@Override
publicvoid onSensorChanged(SensorEvent event) {
float[] values = event.values;
mTextView.setText("Accelerometer:" + values[0] +", "
+ values[1] +", " + values[2]);
}
@Override
publicvoidonAccuracyChanged(Sensor sensor,int accuracy) {
}
};
（4） 注册事件监听器；
protectedvoid onResume() {
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super.onResume();
mSensorManager.registerListener(mEventListener, mSensor,
SensorManager.SENSOR_DELAY_NORMAL);
super.onResume(); mSensorManager.registerListener(mEventListener, mSensor, SensorManager.SENSOR_DELAY_NORMAL); }
（5） 卸载事件监听器；
protectedvoid onPause() {
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super.onPause();
mSensorManager.unregisterListener(mEventListener);
}
super.onPause(); mSensorManager.unregisterListener(mEventListener); }
3 框架 (Framework)
3.1 工作模型
3.1.1 SensorManager的创建
nativeClassInit(): 初始化Native类信息；
sensors_module_init(): 创建Native SensorManager实例，从SensorService读取Sensor设备列表；
sensors_module_get_next_sensor(): 从SensorService读取下一个Sensor设备；
3.1.2 SensorThread数据接收处理
sensors_create_queue(): 创建和SensorService共享的消息队列；
sensors_data_poll(): 从消息队列中读取SensorService发过来的消息；
3.1.3 SensorService的工作原理
SensorDevice::poll(): 调用HAL接口读取数据；
SensorEventConnection::sendEvents(): 往消息队列中写入消息，SensorThread后续会读取该消息；
3.1.4 SensorDevice对HAL的访问
4 硬件抽象层 (HAL)
在linux操作系统中，应用同硬件之间的交互都是通过设备驱动来实现，Android系统为了降低应用开发人员开发难度，屏蔽硬件差异，定义出硬件抽象层，为开发人员提供获取各种设备相关的信息的接口。
4.1 Sensors HAL关键流程
4.1.1 打开Sensor设备
SensorBase ::openInput() : 打开input子系统的sensor消息文件句柄；
ioctl(EVIOCGABS(...)) : 获取ABS_X/ABS_Y/ABS_Z的加速度；
4.1.2 轮循Sensor事件
InputEventCircularReader::fill(): 调用read()从input子系统中读取事件放入环形缓冲区；
InputEventCircularReader::readEvent(): 从环形缓冲区中读取事件；
InputEventCircularReader::next(): 移动环形缓冲区当前指针；
5.2 Sensors HAL关键数据结构
5.2.1 sensors_module_t
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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);
};
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);
};
hw_get_module()会加载HAL模块，并返回HAL入口数据结构(hw_module_t)。HAL_MODULE_INFO_SYM默认是“HAL”，在hw_get_module中用dlsym获取。
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const 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 = "MMA7660 Sensors Module",
.author = "The Android Open Source Project",
.methods = &sensors_module_methods,
},
.get_sensors_list = sensors__get_sensors_list
};
const 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 = "MMA7660 Sensors Module",
.author = "The Android Open Source Project",
.methods = &sensors_module_methods,
},
.get_sensors_list = sensors__get_sensors_list
};
5.2.2 hw_module_methods_t
static struct hw_module_methods_t sensors_module_methods = {
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.open = open_sensors
.open = open_sensors };
5.2.3 sensors_poll_context_t
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struct sensors_poll_context_t {
struct sensors_poll_device_t 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 handleToDriver(int handle);
};
struct sensors_poll_context_t {
struct sensors_poll_device_t 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 handleToDriver(int handle);
};
5.2.4 sensors_poll_device_t
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struct sensors_poll_device_t {
struct hw_device_t common;
int (*activate)(struct sensors_poll_device_t *dev,
int handle, int enabled);
int (*setDelay)(struct sensors_poll_device_t *dev,
int handle, int64_t ns);
int (*poll)(struct sensors_poll_device_t *dev,
sensors_event_t* data, int count);
};
struct sensors_poll_device_t {
struct hw_device_t common;
int (*activate)(struct sensors_poll_device_t *dev,
int handle, int enabled);
int (*setDelay)(struct sensors_poll_device_t *dev,
int handle, int64_t ns);
int (*poll)(struct sensors_poll_device_t *dev,
sensors_event_t* data, int count);
};
5.2.5 sensor_t
定义传感器的基本参数。
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static const struct sensor_t sSensorList[] = {
{ "MMA7660 3-axis Accelerometer",
"Freescale Semiconductor",
1, SENSORS_HANDLE_BASE+ID_A,
SENSOR_TYPE_ACCELEROMETER, 3.0f*9.81f, (3.0f*9.81f)/64.0f, 0.35f, 0, { } },
};
static const struct sensor_t sSensorList[] = {
{ "MMA7660 3-axis Accelerometer",
"Freescale Semiconductor",
1, SENSORS_HANDLE_BASE+ID_A,
SENSOR_TYPE_ACCELEROMETER, 3.0f*9.81f, (3.0f*9.81f)/64.0f, 0.35f, 0, { } },
};
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struct sensor_t {
const char* name;
const char* vendor;
int version;
int handle;
int type;
float maxRange;
float resolution;
float power;
int32_t minDelay;
void* reserved[8];
};
struct sensor_t {
const char* name;
const char* vendor;
int version;
int handle;
int type;
float maxRange;
float resolution;
float power;
int32_t minDelay;
void* reserved[8];
};
6 驱动 (driver)
6.1 mma7660驱动框架
mma7660与主机通信是通过I2C接口，因此mma7660驱动程序采用Linux系统的I2C子系统框架来实现，主要由3部分组成：
(1) I2C核心
I2C核心提供了I2C总线驱动和设备驱动的注册、注销方法，I2C通信方法(即“algorithm”)上层的、与具体适配器无关的代码以及探测设备、检测设备地址的上层代码等。这部分是与平台无关的。
此部分在Linux内核的I2C驱动中实现，mma7660驱动使用其提供的功能接口来注册设备驱动。
(2) I2C总线驱动
I2C总线驱动是对I2C硬件体系结构中适配器端的实现。I2C总线驱动主要包含了I2C适配器数据结构i2c_adapter、I2C适配器的algorithm数据结构i2c_algorithm和控制I2C适配器产生通信信号的函数。经由I2C总线驱动的代码，我们可以控制I2C适配器以主控方式产生开始位、停止位、读写周期，以及以从设备方式被读写、产生ACK等。不同的CPU平台对应着不同的I2C总线驱动。
此部分在Linux内核的I2C驱动中实现，mma7660驱动直接获取其提供的adapter，并调用I2C核心的接口来注册。
(3) I2C设备驱动
I2C设备驱动是对I2C硬件体系结构中设备端的实现。设备一般挂接在受CPU控制的I2C适配器上，通过I2C适配器与CPU交换数据。I2C设备驱动主要包含了数据结构i2c_driver和i2c_client，mma7660驱动需要实现其中的成员函数。
在Linux内核源代码中的drivers目录下的i2c_dev.c文件，实现了I2C适配器设备文件的功能，应用程序通过“i2c-%d”文件名并使用文件操作接口open()、write()、read()、ioctl()和close()等来访问这个设备。应用层可以借用这些接口访问挂接在适配器上的I2C设备的存储空间或寄存器并控制I2C设备的工作方式。
6.2 mma7660操作流程
6.2.1 初始化
6.2.2 探测设备
6.2.3 移除设备
6.2.4 采集数据
6.2.5 睡眠和唤醒
Suspend处理：关闭mma7660模组；
Resume处理：使能mma7660模组；
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static int mma7660_suspend(struct i2c_client *client, pm_message_t mesg)
{
int result;
result = i2c_smbus_write_byte_data(client, MMA7660_MODE,
MK_MMA7660_MODE(0, 0, 0, 0, 0, 0, 0));
assert(result==0);
return result;
}
static int mma7660_resume(struct i2c_client *client)
{
int result;
result = i2c_smbus_write_byte_data(client, MMA7660_MODE,
MK_MMA7660_MODE(0, 1, 0, 0, 0, 0, 1));
assert(result==0);
return result;
}
static struct i2c_driver mma7660_driver = {
.driver = {
.name = MMA7660_DRV_NAME,
.owner = THIS_MODULE,
},
.class = I2C_CLASS_HWMON,
.suspend = mma7660_suspend,
.resume = mma7660_resume,
.probe = mma7660_probe,
.detect = mma7660_detect,
// .address_data = &addr_data,
.remove = __devexit_p(mma7660_remove),
.id_table = mma7660_id,
};
static int mma7660_suspend(struct i2c_client *client, pm_message_t mesg)
{
int result;
result = i2c_smbus_write_byte_data(client, MMA7660_MODE,
MK_MMA7660_MODE(0, 0, 0, 0, 0, 0, 0));
assert(result==0);
return result;
}
static int mma7660_resume(struct i2c_client *client)
{
int result;
result = i2c_smbus_write_byte_data(client, MMA7660_MODE,
MK_MMA7660_MODE(0, 1, 0, 0, 0, 0, 1));
assert(result==0);
return result;
}
static struct i2c_driver mma7660_driver = {
.driver = {
.name = MMA7660_DRV_NAME,
.owner = THIS_MODULE,
},
.class = I2C_CLASS_HWMON,
.suspend = mma7660_suspend,
.resume = mma7660_resume,
.probe = mma7660_probe,
.detect = mma7660_detect,
// .address_data = &addr_data,
.remove = __devexit_p(mma7660_remove),
.id_table = mma7660_id,
};
6.3 命令行调试
6.3.1 sysfs调试接口
（1） 定义sysfs attribute相关数据结构；
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static SENSOR_DEVICE_ATTR(all_axis_force, S_IRUGO, show_xyz_force, NULL, 0);
static SENSOR_DEVICE_ATTR(x_axis_force, S_IRUGO, show_axis_force, NULL, 0);
static SENSOR_DEVICE_ATTR(y_axis_force, S_IRUGO, show_axis_force, NULL, 1);
static SENSOR_DEVICE_ATTR(z_axis_force, S_IRUGO, show_axis_force, NULL, 2);
static SENSOR_DEVICE_ATTR(orientation, S_IRUGO, show_orientation, NULL, 0);
static struct attribute* mma7660_attrs[] =
{
&sensor_dev_attr_all_axis_force.dev_attr.attr,
&sensor_dev_attr_x_axis_force.dev_attr.attr,
&sensor_dev_attr_y_axis_force.dev_attr.attr,
&sensor_dev_attr_z_axis_force.dev_attr.attr,
&sensor_dev_attr_orientation.dev_attr.attr,
NULL
};
static const struct attribute_group mma7660_group =
{
.attrs = mma7660_attrs,
};
static SENSOR_DEVICE_ATTR(all_axis_force, S_IRUGO, show_xyz_force, NULL, 0);
static SENSOR_DEVICE_ATTR(x_axis_force, S_IRUGO, show_axis_force, NULL, 0);
static SENSOR_DEVICE_ATTR(y_axis_force, S_IRUGO, show_axis_force, NULL, 1);
static SENSOR_DEVICE_ATTR(z_axis_force, S_IRUGO, show_axis_force, NULL, 2);
static SENSOR_DEVICE_ATTR(orientation, S_IRUGO, show_orientation, NULL, 0);
static struct attribute* mma7660_attrs[] =
{
&sensor_dev_attr_all_axis_force.dev_attr.attr,
&sensor_dev_attr_x_axis_force.dev_attr.attr,
&sensor_dev_attr_y_axis_force.dev_attr.attr,
&sensor_dev_attr_z_axis_force.dev_attr.attr,
&sensor_dev_attr_orientation.dev_attr.attr,
NULL
};
static const struct attribute_group mma7660_group =
{
.attrs = mma7660_attrs,
};
（2） 在probe函数中创建sysfs文件系统；
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result = sysfs_create_group(&client->dev.kobj, &mma7660_group);
if (result != 0) {
ERR("sysfs_create_group err\n");
goto exit_sysfs_creat_failed;
}
result = sysfs_create_group(&client->dev.kobj, &mma7660_group);
if (result != 0) {
ERR("sysfs_create_group err\n");
goto exit_sysfs_creat_failed;
}
（3） 实现sysfs属性相关的读写函数；
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ssize_t show_orientation(struct device *dev, struct device_attribute *attr, char *buf)
{
int result;
u8 tilt, new_orientation;
mma7660_read_tilt(&tilt);
DBG("tilt [0x%x]\n", tilt);
new_orientation = tilt & 0x1f;
if (orientation!=new_orientation)
orientation = new_orientation;
switch ((orientation>>2)&0x07) {
case 1:
result = sprintf(buf, "Left\n");
break;
case 2:
result = sprintf(buf, "Right\n");
break;
case 5:
result = sprintf(buf, "Downward\n");
break;
case 6:
result = sprintf(buf, "Upward\n");
break;
default:
switch(orientation & 0x03) {
case 1:
result = sprintf(buf, "Front\n");
break;
case 2:
result = sprintf(buf, "Back\n");
break;
default:
result = sprintf(buf, "Unknown\n");
}
}
return result;
}
ssize_t show_orientation(struct device *dev, struct device_attribute *attr, char *buf)
{
int result;
u8 tilt, new_orientation;
mma7660_read_tilt(&tilt);
DBG("tilt [0x%x]\n", tilt);
new_orientation = tilt & 0x1f;
if (orientation!=new_orientation)
orientation = new_orientation;
switch ((orientation>>2)&0x07) {
case 1:
result = sprintf(buf, "Left\n");
break;
case 2:
result = sprintf(buf, "Right\n");
break;
case 5:
result = sprintf(buf, "Downward\n");
break;
case 6:
result = sprintf(buf, "Upward\n");
break;
default:
switch(orientation & 0x03) {
case 1:
result = sprintf(buf, "Front\n");
break;
case 2:
result = sprintf(buf, "Back\n");
break;
default:
result = sprintf(buf, "Unknown\n");
}
}
return result;
}
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ssize_t show_xyz_force(struct device *dev, struct device_attribute *attr, char *buf)
{
int i;
s8 xyz[3];
for (i=0; i<3; i++)
mma7660_read_xyz(i, &xyz[i]);
return sprintf(buf, "(%d,%d,%d)\n", xyz[0], xyz[1], xyz[2]);
}
ssize_t show_axis_force(struct device *dev, struct device_attribute *attr, char *buf)
{
s8 force;
int n = to_sensor_dev_attr(attr)->index;
mma7660_read_xyz(n, &force);
return sprintf(buf, "%d\n", force);
}
ssize_t show_xyz_force(struct device *dev, struct device_attribute *attr, char *buf)
{
int i;
s8 xyz[3];
for (i=0; i<3; i++)
mma7660_read_xyz(i, &xyz[i]);
return sprintf(buf, "(%d,%d,%d)\n", xyz[0], xyz[1], xyz[2]);
}
ssize_t show_axis_force(struct device *dev, struct device_attribute *attr, char *buf)
{
s8 force;
int n = to_sensor_dev_attr(attr)->index;
mma7660_read_xyz(n, &force);
return sprintf(buf, "%d\n", force);
}
6.3.2 Gsensor调试实例
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/sys/devices/platform/gl5201-i2c.1/i2c-1/1-004c # ls
uevent
name
modalias
subsystem
power
driver
all_axis_force
x_axis_force
y_axis_force
z_axis_force
orientation
input
/sys/devices/platform/gl5201-i2c.1/i2c-1/1-004c # cat all_axis_force
(-1,0,22)
/sys/devices/platform/gl5201-i2c.1/i2c-1/1-004c # ls uevent name modalias subsystem power driver all_axis_force x_axis_force y_axis_force z_axis_force orientation input /sys/devices/platform/gl5201-i2c.1/i2c-1/1-004c # cat all_axis_force (-1,0,22)
7 Hardware
7.1 mma7660模组
7.2 关键特性
Sampling Resolution: 6bit
Digital Output (I2C)
3mm x 3mm x 0.9mm DFN Package
Low Power Current Consumption:
Off Mode: 0.4 μA,
Standby Mode: 2 μA,
Active Mode: 47 μA at 1 ODR
Configurable Samples per Second from 1 to 120 samples
Low Voltage Operation:
Analog Voltage: 2.4 V - 3.6 V
Digital Voltage: 1.71 V - 3.6 V
Auto-Wake/Sleep Feature for Low Power Consumption
Tilt Orientation Detection for Portrait/Landscape Capability
Gesture Detection Including Shake Detection and Tap Detection
7.2.1 功能模块图
7.2.2 硬件连接图
7.2.3 运动检测原理
mma7660是一种电容式3轴g-sensor，其技术原理是在wafer的表面做出梳状结构，当产生动作时，由侦测电容差来判断变形量，反推出加速度的值。
简单物理模型如下图：
7.2.4 I2C读写时序
7.2.5 工作状态机
7.2.6 寄存器定义
7.2.7 事件检测
方向和摇动检测
轻拍或倾斜检测
