New line character significance in serial port communication - c

Question

We are testing serial port communication. There are two tty nodes /dev/ttyUSB8 and /dev/ttyUSB9 on the device.
When I transmit buffer from /dev/ttyUSB8 to /dev/ttyUSB9 I don't receive data on the /dev/ttyUSB9 read call if the buffer doesn't contain new line.
Transmit Code
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <termios.h>
#include <unistd.h>
void write_func()
{
int fdw;
int i;
fdw = open("/dev/ttyUSB8", O_RDWR);
printf("fdw : %d\n",fdw);
printf("%ld\n", write(fdw, "Hello", 6));
close(fdw);
}
int main()
{
int i;
write_func();
return 0;
}
Receive Code
void read_thread()
{
int fdr;
char buf[] = "NoData";
fdr = open("/dev/ttyUSB9", O_RDWR);
printf("fdr : %d\n",fdr);
printf("%s: %ld\n", __func__, read(fdr, buf, 6));
printf("%s\n", buf);
close(fdr);
}
int main()
{
int i;
read_thread();
return 0;
}
I don't receive data with the above call, but when I add '\n in the write call i get data in the read block call.
printf("%ld\n", write(fdw, "Hello\n", 7));
What is the significance of new line character in this..
Update:
I added the code to reset canonical mode, still it didn't work:
void write_thread()
{
int fdw;
int i;
struct termios config;
fdw = open("/dev/ttymib24", O_RDWR);
printf("fdw : %d\n",fdw);
tcgetattr(fdw, &config);
config.c_lflag &= ~ICANON;
tcsetattr(fdw, TCSANOW, &config);
printf("%ld\n", write(fdw, "Hello", 6));
close(fdw);
}

Answer 1

Your tty is probably in canonical mode.
Try to reset ICANON by using tcsetattr(). Something like this:
struct termios termiosv;
tcgetattr(fd, &termiosv);
termiosv.c_lflag &= ~ICANON;
tcsetattr(fd, TCSANOW, &termiosv);
More information in man page of termios:
In canonical mode:
* Input is made available line by line. An input line is available
when one of the line delimiters is typed (NL, EOL, EOL2; or EOF at
the start of line). Except in the case of EOF, the line delimiter
is included in the buffer returned by read(2).