I need to implement a Serail port I/O.
what's the difference between with O_NONBLOCK and without it? Note that I have set my c_cc[VTIME] = 0 and c_cc[VMIN] = 0, which means read will return right away no matter if it's a non-blocking mode. The only difference I can see is write(). But it seems the STREAM have enough system buffer to allow write() return right away.

So what's the difference between with and without O_NONBLOCK in question line 1? Thanks

bool mstpInitSerialPort()
{
struct termios SerialIOSetting;
//if ( (fd_SerialPort=open (portname, O_RDWR|O_NOCTTY)) < 0)

if((fd_SerialPort=open(MSTPPORT, O_RDWR|O_NOCTTY/*| O_BLOCK*/))<0) //*****question 1, with and without*****
{
perror("Open Serial Port failed\n");
return false;
}

bzero(&SerialIOSetting, sizeof(SerialIOSetting));

SerialIOSetting.c_cflag = B9600| CRTSCTS| CS8 | CLOCAL | CREAD;
SerialIOSetting.c_iflag = 0; // if == IGNPAR; // ignore parity error
SerialIOSetting.c_oflag = 0; //raw output
SerialIOSetting.c_lflag = 0; // non-canonical, no echo
SerialIOSetting.c_cc[VEOF] = 0xFF;
SerialIOSetting.c_cc[VTIME] = 0; //****Note for question 1
SerialIOSetting.c_cc[VMIN] = 0; //****Note for question 1
tcflush(fd_SerialPort, TCIFLUSH);
if(tcsetattr(fd_SerialPort, TCSANOW, &SerialIOSetting) == -1)
{
perror(strerror(errno));
return false;
}
return true;
}


int SerialRx()
{
int Byte;
if ( read(fd_SerialPort, &Byte, 1) == 1)
return Byte;
else
return -1;
}

bool SerialTxBuf(byte far *txb, word txlen)
{
if( write(fd_SerialPort, txb, txlen) == txlen)
return true;
else
return false;
}

Here is a little help:
http://www.faqs.org/faqs/unix-faq/programmer/faq/

read() is reading from STREAM, where the input characters are buffered. what will happen if the input on serial line is too fast that my read() can't catch up? Thanks.

For example, in the following code, I read one character and do some computation. If the computer connected to my serial port send data very fast, the system buffer endded up to be full and discard characters coming in. How can I know if that happens? By the way, what's the size of the system buffer for STREAM? Thanks


for(; ; )
{
read(fd_serial,&c, 1);
//state machine transformation code
}