Cannot read data from terminal until restarted by other process - terminal

Question

Before adding O_NOCTTY option, my process was killed once by unknown per every booting. I don't know why the process was killed :( and I thought the initializing has some problems. so that I added O_NOCTTY option, and the process was not killed. But it cannot read any data from the buffer until restarted by other process. Please help me :(
The following is code about initializing and reading.
void Init() {
mFd = open("/dev/ttyS2", O_RDWR | O_NOCTTY);
if (mFd > 0)
{
(void)tcgetattr(mFd, &mTermios_p);
speed = B115200;
mTermios_p.c_iflag &= ~(IGNBRK | BRKINT | PARMRK | ISTRIP | INLCR | IGNCR | ICRNL | IXON);
mTermios_p.c_oflag &= ~OPOST;
mTermios_p.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);
mTermios_p.c_cflag &= ~(CSIZE | PARENB);
mTermios_p.c_cflag |= CS8;
mTermios_p.c_cc[VMIN] = 0U;
mTermios_p.c_cc[VTIME] = 0U;
(void)cfsetispeed(&mTermios_p, speed);
(void)cfsetospeed(&mTermios_p, speed);
(void)tcflush(mFd, TCIOFLUSH);
(void)tcsetattr(mFd, TCSANOW, &mTermios_p);
}
else
{
LOGE("uart open failed %s", strerror(errno));
}
}
int32_t Read() {
int32_t bytes = -1;
if (mFd > 0)
{
(void)pthread_mutex_lock(&mMutexLock);
bytes = static_cast<int32_t>(read(mFd, buf, nMaxRead));
(void)pthread_mutex_unlock(&mMutexLock);
}
if (bytes < 0)
{
LOGE("read failed");
}
return bytes;
}

Answer 1

Your serial terminal initialization is essentially the near-equivalent of cfmakeraw() plus setting the baudrate.
However that is insufficient to fully initialize a serial terminal.
At the very least the receiver also has to be enabled:
mTermios_p.c_cflag |= CREAD;
To eliminate any modem handshake issues (especially when there is no modem):
mTermios_p.c_cflag |= CLOCAL;
To eliminate any hardware handshake issues:
mTermios_p.c_cflag &= ~CRTSCTS;
BTW
mTermios_p.c_cc[VMIN] = 0U;
mTermios_p.c_cc[VTIME] = 0U;
Setting both VMIN and VTIME to zero is an ill-advised configuration.
This guide describes this configuration as one that should be used only if "you really, really know what you're doing."
The code that you posted for reading is not capable of (efficiently) handling the consequences of setting both VMIN and VTIME to zero. Unless your program is synchronized with the transmitting program, your read code is likely to "successfully" read zero bytes, i.e. no data.