Linux termios VTIME not working?
- by San Jacinto
We've been bashing our heads off of this one all morning. We've got some serial lines setup between an embedded linux device and an Ubuntu box. Our reads are getting screwed up because our code usually returns two (sometimes more, sometimes exactly one) message reads instead of one message read per actual message sent.
Here is the code that opens the serial port. InterCharTime is set to 4.
void COMBaseClass::OpenPort()
{
cerr<< "openning port"<< port <<"\n";
struct termios newtio;
this->fd = -1;
int fdTemp;
fdTemp = open( port, O_RDWR | O_NOCTTY);
if (fdTemp < 0)
{
portOpen = 0;
cerr<<"problem openning "<< port <<". Retrying"<<endl;
usleep(1000000);
return;
}
newtio.c_cflag = BaudRate | CS8 | CLOCAL | CREAD ;//| StopBits;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
/* set input mode (non-canonical, no echo,...) */
newtio.c_lflag = 0;
newtio.c_cc[VTIME] = InterCharTime; /* inter-character timer in .1 secs */
newtio.c_cc[VMIN] = readBufferSize; /* blocking read until 1 char received */
tcflush(fdTemp, TCIFLUSH);
tcsetattr(fdTemp,TCSANOW,&newtio);
this->fd = fdTemp;
portOpen = 1;
}
The other end is configured similarly for communication, and has one small section of particular iterest:
while (1)
{
sprintf(out, "\r\nHello world %lu", ++ulCount);
puts(out);
WritePort((BYTE *)out, strlen(out)+1);
sleep(2);
} //while
Now, when I run a read thread on the receiving machine, "hello world" is usually broken up over a couple messages. Here is some sample output:
1: Hello
2: world 1
3: Hello
4: world 2
5: Hello
6: world 3
where number followed by a colon is one message recieved. Can you see any error we are making?
Thank you.
Edit:
For clarity, please view section 3.2 of this resource href="http://www.faqs.org/docs/Linux-HOWTO/Serial-Programming-HOWTO.html. To my understanding, with a VTIME of a couple seconds (meaning vtime is set anywhere between 10 and 50, trial-and-error), and a VMIN of 1, there should be no reason that the message is broken up over two separate messages.
