how to read and write data on serial port using threads

Question

I am creating a serial port application in which i am creating two threads one is WRITER THREAD which will write data to serial port and a READER THREAD which will read data from serial port.I know how to open, configure,read and write data on serial port but how to do it using threads.

I am using LINUX(ubuntu) and trying to open ttyS0 port programming in C.

Jonathan Jonathan · Accepted Answer · 2011-03-16T14:07:19

The way I have done this in the past is to set up the port for asynchronous I/O using a VMIN of 0 and a VTIME of, say, 5 deciseconds. The purpose of this was to allow the thread to notice when it was time for the application to shut down, as it could try to read, time out, check for a quit flag, and then try to read some more.

Here is an example read function:

size_t myread(char *buf, size_t len) {
    size_t total = 0;
    while (len > 0) {
        ssize_t bytes = read(fd, buf, len);
        if (bytes == -1) {
            if (errno != EAGAIN && errno != EINTR) {
                // A real error, not something that trying again will fix
                if (total > 0) {
                    return total;
                }
                else {
                    return -1;
                }
            }
        }
        else if (bytes == 0) {
            // EOF
            return total;
        }
        else {
            total += bytes;
            buf += bytes;
            len -= bytes;
        }
    }

    return total;
}

The write function would look as you would expect.

In your setup function, make sure to set:

struct termios tios;
...
tios.c_cflag &= ~ICANON;
tios.c_cc[VMIN] = 0;
tios.c_cc[VTIME] = 5; // You may want to tweak this; 5 = 1/2 second, 10 = 1 second, ...
...

how to read and write data on serial port using threads

2 Answers