首先看下sensor的一个整体大概架构图：
4.0中sensor是以一个service 的方式启动的
在base\cmds\sensorservice\main_sensorservice.cpp
#include <binder/BinderService.h>
#include <SensorService.h>
using namespace android;
int main(int argc, char** argv) {
SensorService::publishAndJoinThreadPool();
return 0;
}
static void publishAndJoinThreadPool(bool allowIsolated = false) {
sp<IServiceManager> sm(defaultServiceManager());
sm->addService(String16(SERVICE::getServiceName()), new SERVICE(), allowIsolated);
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
}
主要是new了一个service并添加到ServiceManager，然后启动线程池
在add service的过程中会调用SensorService的onFirstRef
void SensorService::onFirstRef()
{
ALOGD("nuSensorService starting...");
SensorDevice& dev(SensorDevice::getInstance());//获取sensorSevice实例
if (dev.initCheck() == NO_ERROR) {
sensor_t const* list;
ssize_t count = dev.getSensorList(&list);//获取sensorSevice列表
if (count > 0) {
ssize_t orientationIndex = -1;
bool hasGyro = false;
uint32_t virtualSensorsNeeds =
(1<<SENSOR_TYPE_GRAVITY) |
(1<<SENSOR_TYPE_LINEAR_ACCELERATION) |
(1<<SENSOR_TYPE_ROTATION_VECTOR);
mLastEventSeen.setCapacity(count);
for (ssize_t i=0 ; i<count ; i++) {
registerSensor( new HardwareSensor(list[i]) );//注册各个sensor
switch (list[i].type) {
case SENSOR_TYPE_ORIENTATION:
orientationIndex = i;
break;
case SENSOR_TYPE_GYROSCOPE:
hasGyro = true;
break;
case SENSOR_TYPE_GRAVITY:
case SENSOR_TYPE_LINEAR_ACCELERATION:
case SENSOR_TYPE_ROTATION_VECTOR:
virtualSensorsNeeds &= ~(1<<list[i].type);
break;
}
}
// it's safe to instantiate the SensorFusion object here
// (it wants to be instantiated after h/w sensors have been
// registered)
const SensorFusion& fusion(SensorFusion::getInstance());
if (hasGyro) {//如果有陀螺仪传感器，则虚拟的旋转矢量、重力、线性加速度、方向传感器
// Always instantiate Android's virtual sensors. Since they are
// instantiated behind sensors from the HAL, they won't
// interfere with applications, unless they looks specifically
// for them (by name).
registerVirtualSensor( new RotationVectorSensor() );
registerVirtualSensor( new GravitySensor(list, count) );
registerVirtualSensor( new LinearAccelerationSensor(list, count) );
// these are optional
registerVirtualSensor( new OrientationSensor() );
registerVirtualSensor( new CorrectedGyroSensor(list, count) );
// virtual debugging sensors...
char value[PROPERTY_VALUE_MAX];
property_get("debug.sensors", value, "0");
if (atoi(value)) {
registerVirtualSensor( new GyroDriftSensor() );
}
}
// build the sensor list returned to users
mUserSensorList = mSensorList;
if (hasGyro &&
(virtualSensorsNeeds & (1<<SENSOR_TYPE_ROTATION_VECTOR))) {
// if we have the fancy sensor fusion, and it's not provided by the
// HAL, use our own (fused) orientation sensor by removing the
// HAL supplied one form the user list.
/*if (orientationIndex >= 0) {
mUserSensorList.removeItemsAt(orientationIndex);
}*/
}
run("SensorService", PRIORITY_URGENT_DISPLAY);//启动线程
mInitCheck = NO_ERROR;
}
}
}
onFirstRef主要做了下面三件事:
1构造SensorDevice
SensorDevice::SensorDevice()
: mSensorDevice(0),
mSensorModule(0)
{
status_t err = hw_get_module(SENSORS_HARDWARE_MODULE_ID,
(hw_module_t const**)&mSensorModule);//获取sensor模块
ALOGE_IF(err, "couldn't load %s module (%s)",
SENSORS_HARDWARE_MODULE_ID, strerror(-err));
if (mSensorModule) {
err = sensors_open(&mSensorModule->common, &mSensorDevice);//打开sensor设备
ALOGE_IF(err, "couldn't open device for module %s (%s)",
SENSORS_HARDWARE_MODULE_ID, strerror(-err));
if (mSensorDevice) {
sensor_t const* list;
ssize_t count = mSensorModule->get_sensors_list(mSensorModule, &list);//获取sensor列表
mActivationCount.setCapacity(count);
Info model;
for (size_t i=0 ; i<size_t(count) ; i++) {
mActivationCount.add(list[i].handle, model);
mSensorDevice->activate(mSensorDevice, list[i].handle, 0);
}
}
}
}
2、获取到sensor之后 ，就是注册sensor，开始注册的都是HardwareSensor类型的sensor
void SensorService::registerSensor(SensorInterface* s)
{
sensors_event_t event;
memset(&event, 0, sizeof(event));
const Sensor sensor(s->getSensor());
// add to the sensor list (returned to clients)
mSensorList.add(sensor);
// add to our handle->SensorInterface mapping
mSensorMap.add(sensor.getHandle(), s);
// create an entry in the mLastEventSeen array
mLastEventSeen.add(sensor.getHandle(), event);
}
注册sensor比较简单，主要是添加到几个list和map中。
还有一个registerVirtualSensor，注册虚拟的sensor
void SensorService::registerVirtualSensor(SensorInterface* s)
{
registerSensor(s);
mVirtualSensorList.add( s );
}
调用registerSensor并添加到mVirtualSensorList链表。
3、run启动threadLoop线程
bool SensorService::threadLoop()
{
ALOGD("nuSensorService thread starting...");
const size_t numEventMax = 16;
const size_t minBufferSize = numEventMax + numEventMax * mVirtualSensorList.size();
sensors_event_t buffer[minBufferSize];
sensors_event_t scratch[minBufferSize];
SensorDevice& device(SensorDevice::getInstance());
const size_t vcount = mVirtualSensorList.size();
ssize_t count;
do {
count = device.poll(buffer, numEventMax);//查看sensor上是否有数据到来
if (count<0) {
ALOGE("sensor poll failed (%s)", strerror(-count));
break;
}
recordLastValue(buffer, count);//记录每个sensor的最后一次事件
// handle virtual sensors
if (count && vcount) {
sensors_event_t const * const event = buffer;
const DefaultKeyedVector<int, SensorInterface*> virtualSensors(
getActiveVirtualSensors());//获取虚拟的sensor
const size_t activeVirtualSensorCount = virtualSensors.size();
if (activeVirtualSensorCount) {
size_t k = 0;
SensorFusion& fusion(SensorFusion::getInstance());
if (fusion.isEnabled()) {//融合传感器使能，则调用它的process对根据event数据对SensorFusion里面的一些变量进行设置，
//后面调用其相应的sensor process的时候会用到
for (size_t i=0 ; i<size_t(count) ; i++) {
fusion.process(event[i]);
}
}
for (size_t i=0 ; i<size_t(count) && k<minBufferSize ; i++) {
for (size_t j=0 ; j<activeVirtualSensorCount ; j++) {
if (count + k >= minBufferSize) {
ALOGE("buffer too small to hold all events: "
"count=%u, k=%u, size=%u",
count, k, minBufferSize);
break;
}
sensors_event_t out;
SensorInterface* si = virtualSensors.valueAt(j);
if (si->process(&out, event[i])) {//调用模拟sensor的process处理，输出一个event,添加到buffer
buffer[count + k] = out;
k++;
}
}
}
if (k) {
// record the last synthesized values
recordLastValue(&buffer[count], k);//重新记录每个sensor的最后一次事件
count += k;
// sort the buffer by time-stamps
sortEventBuffer(buffer, count);
}
}
}
// send our events to clients...
const SortedVector< wp<SensorEventConnection> > activeConnections(
getActiveConnections());
size_t numConnections = activeConnections.size();
for (size_t i=0 ; i<numConnections ; i++) {
sp<SensorEventConnection> connection(
activeConnections[i].promote());
if (connection != 0) {
connection->sendEvents(buffer, count, scratch);//把收到的数据传上去
}
}
} while (count >= 0 || Thread::exitPending());
ALOGW("Exiting SensorService::threadLoop => aborting...");
abort();
return false;
}
代码中大概注释了各个比较关键地方的函数意义，主要是收到数据后，查看下如果有虚拟的sensor：
1、 如果使能了SensorFusion，调用它的process对数据进行处理(这里应该是每种类型sensor一次poll最多只会上报一次)，处理过程中会设置相应的一些成员变量值
2、 两个for循环，对所有的event,针对所有的已使能的virtual sensor调用它的process,这里面会用到一些前面第一步设置的一些值，根据输入的event输出一个event并添加到buffer.
数据处理完成后，获取所有活动的连接，并把数据发给它。看一下sendEvents
status_t SensorService::SensorEventConnection::sendEvents(
sensors_event_t const* buffer, size_t numEvents,
sensors_event_t* scratch)
{
// filter out events not for this connection
size_t count = 0;
if (scratch) {
Mutex::Autolock _l(mConnectionLock);
size_t i=0;
while (i<numEvents) {
const int32_t curr = buffer[i].sensor;
if (mSensorInfo.indexOf(curr) >= 0) {//检查在该连接里面是否存在这个sensor,存在则添加到scratch里面
do {
scratch[count++] = buffer[i++];
} while ((i<numEvents) && (buffer[i].sensor == curr));
} else {
i++;
}
}
} else {
scratch = const_cast<sensors_event_t *>(buffer);
count = numEvents;
}
// NOTE: ASensorEvent and sensors_event_t are the same type
ssize_t size = SensorEventQueue::write(mChannel,//将数据写到一个通道
reinterpret_cast<ASensorEvent const*>(scratch), count);
if (size == -EAGAIN) {
// the destination doesn't accept events anymore, it's probably
// full. For now, we just drop the events on the floor.
//ALOGW("dropping %d events on the floor", count);
return size;
}
return size < 0 ? status_t(size) : status_t(NO_ERROR);
}
这样sensorservice就启动起来了
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