Hi,
I am unable to read UART data from COM port ttyS0. Read is being blocked (since it is a blocking call) and it gets triggered and data is read from UART once i run cutecom application. Please let me know if any changes are required for my code given below.

Code :

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>

int main()
{
int fd, n;
char buf[100]= {0};
struct termios options;

fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY );

if (fd == -1)
{
perror("open_port: Unable to open /dev/ttyS0 ");
}
else
{
fcntl(fd, F_SETFL, O_RDWR | O_NOCTTY);
}


if(tcgetattr(fd, &options) != 0)
{
printf("Error %i from tcgetattr: %s\n", errno, strerror(errno));
return 1;
}

options.c_cflag &= ~PARENB;
options.c_cflag &= ~CSTOPB;
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8;
options.c_cflag |= CRTSCTS;
options.c_cflag |= (CREAD | CLOCAL);

options.c_lflag &= ~ICANON;
options.c_lflag &= ~ECHO;
options.c_lflag &= ~ECHOE;
options.c_lflag &= ~ECHONL;
options.c_lflag &= ~ISIG;

options.c_iflag &= ~(IXON | IXOFF | IXANY);
options.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL);

options.c_oflag &= ~OPOST;
options.c_oflag &= ~ONLCR;

options.c_cc[VTIME] = 100;
options.c_cc[VMIN] = 0;

cfsetispeed(&options, B115200);
cfsetospeed(&options, B115200);

if (tcsetattr(fd, TCSANOW, &options) != 0)
{
printf("Error %i from tcsetattr: %s\n", errno, strerror(errno));
return 1;
}

while(1)
{
printf("Waiting to read\n");

n = read(fd, buf, 100);

if(n != 0)
buf[n]='\0';

if (n <= 0)
fputs("read() failed!\n", stderr);
else
printf("read bytes = %d, read val = %s\n", n, buf);

sleep(1);
}
}


Thanks in advance...

Read the "Question Guidelines" link in my posting signature. You haven't told us anything about your system, version/distro of Linux, or even what the actual error(s)/message(s) you're getting are. We're happy to try to help you, but we can't guess...and we aren't going to debug your code for you (which you should post in CODE tags). Also, cutecom appears to be last updated in 2009....may want to consider using minicom or something else more current.

And if your program is opening/reading/writing to a serial port...why do you need cutecom or any other program to ALSO open that port?

Provide details and relevant messages, and we can try to assist.