问题现象：
当休眠后，再次打开preesure sensor的时候，会出现隔一段时候后，APK才会出现数据；（数据有时候会很难出现）
问题分析：
从上面几节中，我们可以知道，framework到HAL是通过调用sensors.msm8909.so调用到函数PressureSensor::readEvents中取出的；
int PressureSensor::readEvents(sensors_event_t* data, int count)
{
int i = 0;
if (count < 1)
return -EINVAL;
if (mHasPendingEvent) {
mHasPendingEvent = false;
mPendingEvent.timestamp = getTimestamp();
*data = mPendingEvent;
return mEnabled ? 1 : 0;
}
if (mHasPendingMetadata) {
mHasPendingMetadata--;
meta_data.timestamp = getTimestamp();
*data = meta_data;
return mEnabled ? 1 : 0;
}
ssize_t n = mInputReader.fill(data_fd);
if (n < 0)
return n;
int numEventReceived = 0;
input_event const* event;
#if FETCH_FULL_EVENT_BEFORE_RETURN
again:
#endif
while (count && mInputReader.readEvent(&event)) {
int type = event->type;
if (type == EV_ABS) {
float value = event->value;
mPendingEvent.pressure = value * CONVERT_PRESSURE;
ALOGI("the pressure is %f\n", mPendingEvent.pressure);
} else if (type == EV_SYN) {
switch (event->code) {
case SYN_TIME_SEC:
mUseAbsTimeStamp = true;
report_time = event->value*1000000000LL;
break;
case SYN_TIME_NSEC:
mUseAbsTimeStamp = true;
mPendingEvent.timestamp = report_time+event->value;
break;
case SYN_REPORT:
if(mUseAbsTimeStamp != true) {
mPendingEvent.timestamp = timevalToNano(event->time);
}
if (mEnabled) {
// ALOGI("timestamp = %ld mEnabledTime = %ld mUseAbsTimeStamp = %d enable here\n", mPendingEvent.timestamp, mEnabledTime, mUseAbsTimeStamp);
// if (mPendingEvent.timestamp >= mEnabledTime)
{
*data = mPendingEvent;
ALOGI("data pressure is %f\n", data->pressure);
// data++;
numEventReceived++;
}
count--;
}
break;
}
} else {
ALOGE("PressureSensor: unknown event (type=%d, code=%d)",
type, event->code);
}
mInputReader.next();
}
#if FETCH_FULL_EVENT_BEFORE_RETURN
/* if we didn't read a complete event, see if we can fill and
try again instead of returning with nothing and redoing poll. */
if (numEventReceived == 0 && mEnabled == 1) {
n = mInputReader.fill(data_fd);
if (n)
goto again;
}
#endif
ALOGI("end the data the pressure is %f\n", mPendingEvent.pressure);
return numEventReceived;
}增加if (mPendingEvent.timestamp >= mEnabledTime)判断是为了判断SYN_REPORT不延迟的情况；
mPendingEvent.timestamp在这里被赋值：
input_event const* event; //这个可以一直进来 if(mUseAbsTimeStamp != true) { mPendingEvent.timestamp = timevalToNano(event->time); }
event->time代表了按键时间；可以用struct timeval获取系统时间。
其中input_event和timeval结构体如下：struct input_event { struct timeval time; //按键时间 __u16 type; //类型，在下面有定义 __u16 code; //要模拟成什么按键 __s32 value;//是按下还是释放 }; struct timeval { __kernel_time_t tv_sec; /* seconds */ __kernel_suseconds_t tv_usec; /* microseconds */ };//将时间转换为ns static int64_t timevalToNano(timeval const& t) { return t.tv_sec*1000000000LL + t.tv_usec*1000; }通过打印可以知道问题出现的时候
mPendingEvent.timestamp是小于mEnabledTime的，进不了判断，所以上层也就无法获取相应的数据；
mEnabledTime是在int PressureSensor::enable(int32_t, int en)函数中实现：
....
mEnabledTime = getTimestamp() + IGNORE_EVENT_TIME;
....int64_t SensorBase::getTimestamp() {
struct timespec t;
t.tv_sec = t.tv_nsec = 0;
clock_gettime(CLOCK_BOOTTIME, &t);
return int64_t(t.tv_sec)*1000000000LL + t.tv_nsec;
}
//不过CLOCK_BOOTTIME计算系统suspend的时间，也就是说，不论是running还是suspend（这些都算是启动时间），CLOCK_BOOTTIME都会累积计时，直到系统reset或者shutdown。所以在睡眠起来后mEnabledTime会大于mPendingEvent.timestamp，所以此时是没有上报数据的；将判断去掉即可；