Are you opening the serial port with all the right options?  I've never had that
happen, but it sounds like some sort of echo.  Do you know that the device you
are reading from is not actually sending the newlines?

Here is my serial port initialization function.  You'll need to set the options
to what you need, but...  Maybe you will find something missing in your code.
I've used this exact code in several projects over the last year.  Including one
just a few weeks ago, so I know it works.

Just pass this function the port number and it returns a file descriptor to the
open port.


int initialize_serial(int port_num)
{
        struct termios options;
        int fd=0;

        //open port
        switch(port_num)
        {
                case 0:
                        fd=open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
                        break;
                case 1:
                        fd=open("/dev/ttyS1", O_RDWR | O_NOCTTY | O_NDELAY);
                        break;
                case 2:
                        fd=open("/dev/ttyS2", O_RDWR | O_NOCTTY | O_NDELAY);
                        break;
                case 3:
                        fd=open("/dev/ttyS3", O_RDWR | O_NOCTTY | O_NDELAY);
                        break;
        }

        //make sure it opened okay
        if(fd==-1)
        {
                printf("Error opening serial port\r\n");
        }

        fcntl(fd, F_SETFL, 0);

        //get the current port options
        tcgetattr(fd, &options);

        //set baud rate
        cfsetispeed(&options, B38400);
        cfsetospeed(&options, B38400);

        //set up port for 8N1
        options.c_cflag |= (CLOCAL | CREAD);
        options.c_cflag &= ~PARENB;
        options.c_cflag &= ~CSTOPB;
        options.c_cflag &= ~CSIZE;
        options.c_cflag |= CS8;

        //options.c_lflag |= (ICANON);
        options.c_lflag &= ~(ECHO | ECHOE | ECHOK | ECHONL | ISIG);

        options.c_cc[VTIME]=0;
        options.c_cc[VMIN]=6;

        //apply new settings
        tcsetattr(fd, TCSANOW, &options);

        return fd;
}



Good luck,
Eric



On Mon, 16 Feb 2004 15:12:28 -0500
Herbert Graf <mailinglist2@FARCITE.NET> wrote:

> Hello all,
>
> I'm trying to write a small program that sends a few things over a serial
> port and then reads a few things back. I've having trouble getting it to
> work.
>
> I'm using open, write and read to do my things, accessing the device through
> the /dev/ttyS1 interface. Things work fine for a while and then seem to go
> crazy. For example, I can send a few things down the line, but then when I
> do a single byte read from the port I continuously get the newline
> character.
>
> Anybody have some simple gcc compatible c code of accessing the serial port
> in Linux? I'm using Redhat 9.0 and gcc. Thanks, TTYL
>
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