一，Android sensor 系统架构
Hal 就是对Linux内核驱动程序的封装，向上提供接口，屏蔽低层的实现细节。也就是说，把对硬件的支持分成了两层，一层放在用户空间（User Space），一层放在内核空间（Kernel Space），其中，硬件抽象层运行在用户空间，而Linux内核驱动程序运行在内核空间。
二，HAL 层Sensor 框架实现
Sensor HAL层相对来说比较简单，它的意图就是为framework层提供接口API的实现，如open_sensors,poll等，一旦实现完毕，framewoerk 里面的SensorManager,SensorService 里面的native(本地)方法可以直接被调用。
2.1 HAL 客制化
在alps\device\mediatek$(proj)\ProjectConfig.mk中 配置对应的传感器为y
等效路径（kernel3.18\arch\arm64\configs$(proj).deconfig）
CONFIG_MTK_SENSOR_SUPPORT=y
CONFIG_CUSTOM_KERNEL_ACCELEROMETER=y
CONFIG_MTK_ICM20645G=y
CONFIG_CUSTOM_KERNEL_ALSPS=y
CONFIG_MTK_CM36558=y
CONFIG_CUSTOM_KERNEL_GYROSCOPE=y
CONFIG_MTK_ICM20645GY=y
2.2 获取module函数
Hal层的库文件是怎么被上层调用的？上层调用时的入口(相当于main)又是什么呢？它就是HAL_MODULE_INFO_SYM。
路径：vendor/mediatek/proprietary/hardware/sensor/sensors.c
static int open_sensors(const struct hw_module_t* module, const char* name,
struct hw_device_t** device)
{
ALOGD("%s: name: %s! fwq debug\r\n", __func__, name);
return init_nusensors(module, device);
}
static struct hw_module_methods_t sensors_module_methods = {
.open = open_sensors
};
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 = "MTK SENSORS Module",
.author = "Mediatek",
.methods = &sensors_module_methods,
},
.get_sensors_list = sensors__get_sensors_list,
};
路径：vendor/mediatek/proprietary/hardware/sensor/nusensors.cpp
int init_nusensors(hw_module_t const* module, hw_device_t** device)
{
int status = -EINVAL;
dev = new sensors_poll_context_t();
memset(&dev->device, 0, sizeof(sensors_poll_device_1));
dev->device.common.tag = HARDWARE_DEVICE_TAG;
#if defined(SENSOR_BATCH_SUPPORT) || defined(CUSTOM_KERNEL_SENSORHUB)
dev->device.common.version = SENSORS_DEVICE_API_VERSION_1_1;
#else
dev->device.common.version = SENSORS_DEVICE_API_VERSION_1_0;
#endif
dev->device.common.module = const_cast<hw_module_t*>(module);
dev->device.common.close = poll__close;
dev->device.activate = poll__activate;
dev->device.setDelay = poll__setDelay;
dev->device.poll = poll__poll;
dev->device.batch = poll__batch;
dev->device.flush = poll__flush;
*device = &dev->device.common;
status = 0;
return status;
}
2.3 创建 sensors_poll_context_t 对象
sensors_poll_context_t::sensors_poll_context_t()
{
memset(&device, 0, sizeof(device));
mSensors[accel] = new AccelerationSensor();
mPollFds[accel].fd = ((AccelerationSensor*)mSensors[accel])->mdata_fd;
mPollFds[accel].events = POLLIN;
mPollFds[accel].revents = 0;
mSensors[proximity] = new ProximitySensor();
mPollFds[proximity].fd = ((ProximitySensor*)mSensors[proximity])->mdata_fd;
mPollFds[proximity].events = POLLIN;
mPollFds[proximity].revents = 0;
int wakeFds[2];
int result = pipe(wakeFds);
if (result < 0) {
ALOGE_IF(result < 0, "error creating wake pipe (%s)", strerror(errno));
mWritePipeFd = -1;
} else {
result = fcntl(wakeFds[0], F_SETFL, O_NONBLOCK);
ALOGE_IF(result < 0, "fcntl(wakeFds[0] fail (%s)", strerror(errno));
result = fcntl(wakeFds[1], F_SETFL, O_NONBLOCK);
ALOGE_IF(result < 0, "fcntl(wakeFds[1] fail (%s)", strerror(errno));
mWritePipeFd = wakeFds[1];
}
mPollFds[wake].fd = wakeFds[0];
mPollFds[wake].events = POLLIN;
mPollFds[wake].revents = 0;
}
2.4 创建Sensor对象
路径：vendor/mediatek/proprietary/hardware/sensor/Proximity.cpp
ProximitySensor::ProximitySensor()
: SensorBase(NULL, "m_alsps_input"),//PRO_INPUTDEV_NAME
mEnabled(0),
mInputReader(32)
{
char datapath[64]={"/sys/class/misc/m_alsps_misc/psactive"};
int fd = -1;
char buf[64]={0};
int len;
mdata_fd = FindDataFd();
if (mdata_fd >= 0) {
strcpy(input_sysfs_path, "/sys/class/misc/m_alsps_misc/");
input_sysfs_path_len = strlen(input_sysfs_path);
}
else
{
ALOGE("couldn't find input device ");
return;
}
ALOGD("prox misc path =%s", input_sysfs_path);
fd = open(datapath, O_RDWR);
if (fd >= 0)
{
len = read(fd,buf,sizeof(buf)-1);
if (len <= 0)
{
ALOGD("read div err, len = %d", len);
}
else
{
buf[len] = '\0';
sscanf(buf, "%d", &mDataDiv);
ALOGD("read div buf(%s), mdiv %d", datapath,mDataDiv);
}
close(fd);
}
else
{
ALOGE("open acc misc path %s fail ", datapath);
}
}
2.5 通用sensor 的使能函数
static int poll__activate(struct sensors_poll_device_t *dev,
int handle, int enabled) {
sensors_poll_context_t *ctx = (sensors_poll_context_t *)dev;
return ctx->activate(handle-ID_OFFSET, enabled);
}
int sensors_poll_context_t::activate(int handle, int enabled)
{
....
int index = handleToDriver(handle);
.....
if(NULL != mSensors[index])
{
ALOGD( "use new sensor index=%d, mSensors[index](%x)", index, mSensors[index]);
if(this->device.common.version >= SENSORS_DEVICE_API_VERSION_1_1)
{
ALOGD("support batch active \n" );
mSensors[batchsensor]->enable(handle, enabled);
}
err = mSensors[index]->enable(handle, enabled);
}
return err;
}
2.6 封装poll 函数
poll 函数对应framework中poll操作，这里只需了解它的功能实现，调用逻辑需要查看framework层代码
poll 是一个非常重要的接口，它的实现基于linux 内核中IO多路复用策略（一种效率非常高的机制）
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);
}
轮询事件方法，这是一个构造方法，该对象创建，会启动轮询机制，监听sensorlist[]中文件描述符，等待事件上报 （使用IO多路复用策略）
int sensors_poll_context_t::pollEvents(sensors_event_t* data, int count)
{
.....
do {
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 (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
n = poll(mPollFds, numFds, nbEvents ? 0 : -1);
if (n<0) {
int err;
err = errno;
ALOGE("poll() failed (%s)", strerror(errno));
return -err;
}
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;
}
2.7 读取事件函数
int ProximitySensor::readEvents(sensors_event_t* data, int count)
{
....
ssize_t n = mInputReader.fill(mdata_fd);
if (n < 0)
return n;
int numEventReceived = 0;
input_event const* event;
while (count && mInputReader.readEvent(&event)) {
int type = event->type;
//ALOGE("fwq1....\r\n");
if (type == EV_REL)
{
processEvent(event->code, event->value);
//ALOGE("fwq2....\r\n");
}
.....
mInputReader.next();
}
//ALOGE("fwq read Event 2\r\n");
return numEventReceived;
}
void ProximitySensor::processEvent(int code, int value)
{
ALOGD("processEvent code=%d,value=%d\r\n",code, value);
switch (code) {
case EVENT_TYPE_PS_VALUE:
mPendingEvent.distance= value-1;
break;
}
}
2.8 获得sensor 列表函数
路径：vendor/mediatek/proprietary/hardware/sensor/sensors.c
这一步非常重要，HAL_MODULE_INFO_SYM 映射了hal 层XXX.so 库的入口，上层hw_get_module 将获得该入口，使得上层可以和底层.so库进行交互
static int sensors__get_sensors_list(struct sensors_module_t* module,
struct sensor_t const** list)
{
ALOGD(" sSensorList addr =%p, module addr =%p\r\n",sSensorList,module);
ALOGD(" ARRAY_SIZE(sSensorList) =%d SENSORS_NUM=%d MAX_NUM_SENSOR=%d \r\n",ARRAY_SIZE(sSensorList), SENSORS_NUM, MAX_NUM_SENSOR);
*list = sSensorList;
return ARRAY_SIZE(sSensorList);
}
struct sensor_t sSensorList[] =
{
#ifdef CUSTOM_KERNEL_ACCELEROMETER
{
.name = ACCELEROMETER,
.vendor = ACCELEROMETER_VENDER,
.version = 3,
.handle = ID_ACCELEROMETER+ID_OFFSET,
.type = SENSOR_TYPE_ACCELEROMETER,
.maxRange = ACCELEROMETER_RANGE,//32.0f,
.resolution = ACCELEROMETER_RESOLUTION,//4.0f/1024.0f,
.power = ACCELEROMETER_POWER,//130.0f/1000.0f,
.minDelay = 10000,
.maxDelay = 1000000,
.reserved = {}
},
#endif
#if defined(CUSTOM_KERNEL_ALSPS) || defined(CUSTOM_KERNEL_ALS)
{
.name = LIGHT,
.vendor = LIGHT_VENDER,
.version = 1,
.handle = ID_LIGHT+ID_OFFSET,
.type = SENSOR_TYPE_LIGHT,
.maxRange = LIGHT_RANGE,//10240.0f,
.resolution = LIGHT_RESOLUTION,//1.0f,
.power = LIGHT_POWER,//0.13f,
.reserved = {}
},
#endif
};
三，Selinux权限问题
四，HAL 层log分析
psensor 手机中常见的使用就是拨号时贴脸灭屏，拨号后遮挡psensor，使用Adb抓取android log ,过滤的的psensor log部分如下：
驱动部分后续再介绍