(OK) android-5.0 sensor工作原理—sensorservice的启动(二)

http://blog.csdn.net/zsj100213/article/details/48287023

3.2 dev.getSensorList(&list);获取厂商在HAL层初始化的sensor_t类型结构体的sSensorList，并返回sensor device的数目。

3.3 registerSensor( new HardwareSensor(list[i]) );在for循环中注册这些sensor。根据硬件sensor_t创建HardwareSensor,然后加入mSensorList(Sensor) 和mSensorMap(HardwareSensor)中，后面的switch是判断是否存在电子罗盘，GYRO以及GYRO对应所需要的对应的一些所对应的一些虚拟sensor

for (ssize_t i=0 ; i<count ; i++) {
               registerSensor( new HardwareSensor(list[i]) );
               switch (list[i].type) {
                   case SENSOR_TYPE_ORIENTATION:
                       orientationIndex = i;
                       break;
                   case SENSOR_TYPE_GYROSCOPE:
                   case SENSOR_TYPE_GYROSCOPE_UNCALIBRATED:
                       hasGyro = true;
                       break;
                   case SENSOR_TYPE_GRAVITY:
                   case SENSOR_TYPE_LINEAR_ACCELERATION:
                   case SENSOR_TYPE_ROTATION_VECTOR:
                       virtualSensorsNeeds &= ~(1<<list[i].type);
                       break;
               }

Sensor 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);

    return sensor;
}

3.4 mUserSensorList = mSensorList;将mSensorList传感器列表赋值给mUserSensorList，mSensorList是由registerSensor初始化的，mUserSensorList是要提交给Java框架层的传感器列表。

3.5 如果有GYRO就注册这样一些上面提到的三种虚拟sensor来实现GYRO的功能，此处我是这么理解的。

if (hasGyro) {
               Sensor aSensor;

               // Add Android virtual sensors if they're not already
               // available in the HAL

               aSensor = registerVirtualSensor( new RotationVectorSensor() );
               if (virtualSensorsNeeds & (1<<SENSOR_TYPE_ROTATION_VECTOR)) {
                   mUserSensorList.add(aSensor);
               }

               aSensor = registerVirtualSensor( new GravitySensor(list, count) );
               if (virtualSensorsNeeds & (1<<SENSOR_TYPE_GRAVITY)) {
                   mUserSensorList.add(aSensor);
               }

               aSensor = registerVirtualSensor( new LinearAccelerationSensor(list, count) );
               if (virtualSensorsNeeds & (1<<SENSOR_TYPE_LINEAR_ACCELERATION)) {
                   mUserSensorList.add(aSensor);
               }

               aSensor = registerVirtualSensor( new OrientationSensor() );
               if (virtualSensorsNeeds & (1<<SENSOR_TYPE_ROTATION_VECTOR)) {
                   // if we are doing our own rotation-vector, also add
                   // the orientation sensor and remove the HAL provided one.
                   mUserSensorList.replaceAt(aSensor, orientationIndex);
               }

               // virtual debugging sensors are not added to mUserSensorList
               registerVirtualSensor( new CorrectedGyroSensor(list, count) );
               registerVirtualSensor( new GyroDriftSensor() );
           }

3.6 run("SensorService", PRIORITY_URGENT_DISPLAY);启动sensorService线程，sensorService父类有一个Thread线程，调用run方法会创建线程并调用threadLoop方法。

bool SensorService::threadLoop()
{
    ALOGD("nuSensorService thread starting...");

    // each virtual sensor could generate an event per "real" event, that's why we need
    // to size numEventMax much smaller than MAX_RECEIVE_BUFFER_EVENT_COUNT.
    // in practice, this is too aggressive, but guaranteed to be enough.
    const size_t minBufferSize = SensorEventQueue::MAX_RECEIVE_BUFFER_EVENT_COUNT;
    const size_t numEventMax = minBufferSize / (1 + mVirtualSensorList.size());

    SensorDevice& device(SensorDevice::getInstance());
    const size_t vcount = mVirtualSensorList.size();

    SensorEventAckReceiver sender(this);
    sender.run("SensorEventAckReceiver", PRIORITY_URGENT_DISPLAY);
    const int halVersion = device.getHalDeviceVersion();
    do {
        ssize_t count = device.poll(mSensorEventBuffer, numEventMax);
        if (count < 0) {
            ALOGE("sensor poll failed (%s)", strerror(-count));
            break;
        }

        // Reset sensors_event_t.flags to zero for all events in the buffer.
        for (int i = 0; i < count; i++) {
             mSensorEventBuffer[i].flags = 0;
        }

        // Make a copy of the connection vector as some connections may be removed during the
        // course of this loop (especially when one-shot sensor events are present in the
        // sensor_event buffer). Promote all connections to StrongPointers before the lock is
        // acquired. If the destructor of the sp gets called when the lock is acquired, it may
        // result in a deadlock as ~SensorEventConnection() needs to acquire mLock again for
        // cleanup. So copy all the strongPointers to a vector before the lock is acquired.
        SortedVector< sp<SensorEventConnection> > activeConnections;
        {
            Mutex::Autolock _l(mLock);
            for (size_t i=0 ; i < mActiveConnections.size(); ++i) {
                sp<SensorEventConnection> connection(mActiveConnections[i].promote());
                if (connection != 0) {
                    activeConnections.add(connection);
                }
            }
        }

        Mutex::Autolock _l(mLock);
        // Poll has returned. Hold a wakelock if one of the events is from a wake up sensor. The
        // rest of this loop is under a critical section protected by mLock. Acquiring a wakeLock,
        // sending events to clients (incrementing SensorEventConnection::mWakeLockRefCount) should
        // not be interleaved with decrementing SensorEventConnection::mWakeLockRefCount and
        // releasing the wakelock.
        bool bufferHasWakeUpEvent = false;
        for (int i = 0; i < count; i++) {
            if (isWakeUpSensorEvent(mSensorEventBuffer[i])) {
                bufferHasWakeUpEvent = true;
                break;
            }
        }

        if (bufferHasWakeUpEvent && !mWakeLockAcquired) {
            acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_NAME);
            mWakeLockAcquired = true;
        }
        recordLastValueLocked(mSensorEventBuffer, count);

        // handle virtual sensors
        if (count && vcount) {
            sensors_event_t const * const event = mSensorEventBuffer;
            const size_t activeVirtualSensorCount = mActiveVirtualSensors.size();
            if (activeVirtualSensorCount) {
                size_t k = 0;
                SensorFusion& fusion(SensorFusion::getInstance());
                if (fusion.isEnabled()) {
                    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=%zd, k=%zu, size=%zu",
                                    count, k, minBufferSize);
                            break;
                        }
                        sensors_event_t out;
                        SensorInterface* si = mActiveVirtualSensors.valueAt(j);
                        if (si->process(&out, event[i])) {
                            mSensorEventBuffer[count + k] = out;
                            k++;
                        }
                    }
                }
                if (k) {
                    // record the last synthesized values
                    recordLastValueLocked(&mSensorEventBuffer[count], k);
                    count += k;
                    // sort the buffer by time-stamps
                    sortEventBuffer(mSensorEventBuffer, count);
                }
            }
        }

        // handle backward compatibility for RotationVector sensor
        if (halVersion < SENSORS_DEVICE_API_VERSION_1_0) {
            for (int i = 0; i < count; i++) {
                if (mSensorEventBuffer[i].type == SENSOR_TYPE_ROTATION_VECTOR) {
                    // All the 4 components of the quaternion should be available
                    // No heading accuracy. Set it to -1
                    mSensorEventBuffer[i].data[4] = -1;
                }
            }
        }

        // Map flush_complete_events in the buffer to SensorEventConnections which called
        // flush on the hardware sensor. mapFlushEventsToConnections[i] will be the
        // SensorEventConnection mapped to the corresponding flush_complete_event in
        // mSensorEventBuffer[i] if such a mapping exists (NULL otherwise).
        for (int i = 0; i < count; ++i) {
            mMapFlushEventsToConnections[i] = NULL;
            if (mSensorEventBuffer[i].type == SENSOR_TYPE_META_DATA) {
                const int sensor_handle = mSensorEventBuffer[i].meta_data.sensor;
                SensorRecord* rec = mActiveSensors.valueFor(sensor_handle);
                if (rec != NULL) {
                    mMapFlushEventsToConnections[i] = rec->getFirstPendingFlushConnection();
                    rec->removeFirstPendingFlushConnection();
                }
            }
        }

        // Send our events to clients. Check the state of wake lock for each client and release the
        // lock if none of the clients need it.
        bool needsWakeLock = false;
        size_t numConnections = activeConnections.size();
        for (size_t i=0 ; i < numConnections; ++i) {
            if (activeConnections[i] != 0) {
                activeConnections[i]->sendEvents(mSensorEventBuffer, count, mSensorEventScratch,
                        mMapFlushEventsToConnections);
                needsWakeLock |= activeConnections[i]->needsWakeLock();
                // If the connection has one-shot sensors, it may be cleaned up after first trigger.
                // Early check for one-shot sensors.
                if (activeConnections[i]->hasOneShotSensors()) {
                    cleanupAutoDisabledSensorLocked(activeConnections[i], mSensorEventBuffer,
                            count);
                }
            }
        }

        if (mWakeLockAcquired && !needsWakeLock) {
            release_wake_lock(WAKE_LOCK_NAME);
            mWakeLockAcquired = false;
        }
    } while (!Thread::exitPending());

    ALOGW("Exiting SensorService::threadLoop => aborting...");
    abort();
    return false;
}

3.6.1 首先是调用device.poll(mSensorEventBuffer, numEventMax);来获取sensor数据。这里调用的是前面open_sensors函数初始化的 dev->device.poll            = poll__poll;

static int poll__poll(struct sensors_poll_device_t *dev,
        sensors_event_t* data, int count) {
    sensors_poll_context_t *ctx = (sensors_poll_context_t *)dev;
    return ctx->pollEvents(data, count);
}

可以看到最后调用的是pollEvents函数：

int sensors_poll_context_t::pollEvents(sensors_event_t * data, int count)
{
    int nbEvents = 0;
    int n = 0;
    int polltime = -1;

    do {
        // see if we have some leftover from the last poll()
        for (int i = 0; count && i < numSensorDrivers; i++) {
            SensorBase *const sensor(mSensors[i]);
            if ((mPollFds[i].revents & POLLIN)
                || (sensor->hasPendingEvents())) {
                int nb = sensor->readEvents(data, count);
                if (nb < count) {
                    // no more data for this sensor
                    mPollFds[i].revents = 0;
                }
#ifndef ORI_NULL
                if ((0 != nb) && (acc == i)) {
                    ((OriSensor *) (mSensors[ori]))->
                        setAccel(&data[nb - 1]);
                }
#endif
                count -= nb;
                nbEvents += nb;
                data += nb;
            }
        }

        if (count) {
            // we still have some room, so try to see if we can get
            // some events immediately or just wait if we don't have
            // anything to return
            do {
                n = poll(mPollFds, numFds,
                     nbEvents ? 0 : polltime);
            } while (n < 0 && errno == EINTR);
            if (n < 0) {
                ALOGE("poll() failed (%s)", strerror(errno));
                return -errno;
            }
            if (mPollFds[wake].revents & POLLIN) {
                char msg;
                int result = read(mPollFds[wake].fd, &msg, 1);
                ALOGE_IF(result < 0,
                     "error reading from wake pipe (%s)",
                     strerror(errno));
                ALOGE_IF(msg != WAKE_MESSAGE,
                     "unknown message on wake queue (0x%02x)",
                     int (msg));
                mPollFds[wake].revents = 0;
            }
        }
        // if we have events and space, go read them
    } while (n && count);

    return nbEvents;
}

这里首先调用的是sensor->readEvents(data, count);也就是各个sensor对应的读取sensor event的方法。readEvents()函数先调用fill函数将所要读的sensor的input_event事件读取到一个环形缓冲区，然后在while循环中mInputReader.readEvent(&event)读取当前指针所指向的事件，mInputReader.next();将指针指向环形队列下一条事件来读取下一条事件。

int STKLightSensor::readEvents(sensors_event_t* data, int count){
    if (count < 1)
        return -EINVAL;

    if (mHasPendingEvent) {
        mHasPendingEvent = false;
        mPendingEvent.timestamp = getTimestamp();
        *data = mPendingEvent;
        return mEnabled ? 1 : 0;
    }

    ssize_t n = mInputReader.fill(data_fd);
    if (n < 0)
        return n;

    int numEventReceived = 0;
    input_event const* event;

    while (count && mInputReader.readEvent(&event)) {
        int type = event->type;
        if (type == EV_ABS) {
            if (event->code == ABS_MISC) {
                mPendingEvent.light = (float)event->value;
            }
        } else if (type == EV_SYN) {
            mPendingEvent.timestamp = timevalToNano(event->time);
            if (mEnabled) {
                *data++ = mPendingEvent;
                count--;
                numEventReceived++;
            }
        } else {
            ALOGE("STKLightSensor: unknown event (type=%d, code=%d)",
                    type, event->code);
        }
        mInputReader.next();
    }

    return numEventReceived;
}

fill函数的参数data_fd是在前面sensors_poll_context_t()函数中的new STKLightSensor();进行初始化的，其主要是SensorBase(NULL, "lightsensor-level")，这里主要是openInput动作来获得一个fd从而从这个fd的文件中获取sensor event。

ssize_t InputEventCircularReader::fill(int fd)
{
    size_t numEventsRead = 0;
    if (mFreeSpace) {
        const ssize_t nread =
            read(fd, mHead, mFreeSpace * sizeof(input_event));
        if (nread < 0 || nread % sizeof(input_event)) {
            // we got a partial event!!
            return nread < 0 ? -errno : -EINVAL;
        }

        numEventsRead = nread / sizeof(input_event);
        if (numEventsRead) {
            mHead += numEventsRead;
            mFreeSpace -= numEventsRead;
            if (mHead > mBufferEnd) {
                size_t s = mHead - mBufferEnd;
                memcpy(mBuffer, mBufferEnd,
                       s * sizeof(input_event));
                mHead = mBuffer + s;
            }
        }
    }

    return numEventsRead;
}

ssize_t InputEventCircularReader::readEvent(input_event const **events)
{
    *events = mCurr;
    ssize_t available = (mBufferEnd - mBuffer) - mFreeSpace;
    return available ? 1 : 0;
}

void InputEventCircularReader::next()
{
    mCurr++;
    mFreeSpace++;
    if (mCurr >= mBufferEnd) {
        mCurr = mBuffer;
    }
}

SensorBase::SensorBase(
        const char* dev_name,
        const char* data_name)
    : dev_name(dev_name), data_name(data_name),
      dev_fd(-1), data_fd(-1)
{
    if (data_name) {
        data_fd = openInput(data_name);
    }
}

openInput()实际上是打开各个sensor对应于/dev/input/event*文件节点最后返回的是sensor对应文件节点的fd，也就是上面fill函数的参数data_fd，在adb shell，然后getevent命令也是获取位于/dev/input/下所有的event事件。

int SensorBase::openInput(const char* inputName) {
    int fd = -1;
    const char *dirname = "/dev/input";
    char devname[PATH_MAX];
    char *filename;
    DIR *dir;
    struct dirent *de;
    dir = opendir(dirname);
    if(dir == NULL)
        return -1;
    strcpy(devname, dirname);
    filename = devname + strlen(devname);
    *filename++ = '/';
    while((de = readdir(dir))) {
        if(de->d_name[0] == '.' &&
                (de->d_name[1] == '' ||
                        (de->d_name[1] == '.' && de->d_name[2] == '')))
            continue;
        strcpy(filename, de->d_name);
        fd = open(devname, O_RDONLY);
        if (fd>=0) {
            char name[80];
            if (ioctl(fd, EVIOCGNAME(sizeof(name) - 1), &name) < 1) {
                name[0] = '';
            }
            if (!strcmp(name, inputName)) {
                strcpy(input_name, filename);
                break;
            } else {
                close(fd);
                fd = -1;
            }
        }
    }
    closedir(dir);
    ALOGE_IF(fd<0, "couldn't find '%s' input device", inputName);
    return fd;

在获取完数据之后就要通过 activeConnections[i]->sendEvents(mSensorEventBuffer, count, mSensorEventScratch,mMapFlushEventsToConnections);调用write函数将数据放到一个管道里面，sensor APP将数据取走。

ssize_t size = SensorEventQueue::write(mChannel,
                                reinterpret_cast<ASensorEvent const*>(scratch), count);

至此sensorservice的启动就讲完了，下一篇将从sensor APP端讲述sensor APP的工作流程。