Re: Regarding USB-to-serial device driver

[Raju Rameshwar Uprade]

Hi Greg,

> > Is it possible to control RTS line from user space.
> 
> Yes.
 
It's  possible to control RTS line for standard UART serial port like ttyS0 and ttyS1
from userspace.

But for USB-to-serial port like ttyUSB0, the program is not able to control RTS line
from userspace.

I have attached the userspace program for enable/disable of RTS line.

Thanks-

Raj
#include <stdio.h>
#include <stdlib.h>
#include <termios.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


static struct termios oldterminfo;


void closeserial(int fd)
{
    tcsetattr(fd, TCSANOW, &oldterminfo);
    if (close(fd) < 0)
        perror("closeserial()");
}


int openserial(char *devicename)
{
    int fd;
    struct termios attr;

    if ((fd = open(devicename, O_RDWR)) == -1) {
        perror("openserial(): open()");
        return 0;
    }
    if (tcgetattr(fd, &oldterminfo) == -1) {
        perror("openserial(): tcgetattr()");
        return 0;
    }
    attr = oldterminfo;
    attr.c_cflag |= CRTSCTS | CLOCAL;
    attr.c_oflag = 0;
    if (tcflush(fd, TCIOFLUSH) == -1) {
        perror("openserial(): tcflush()");
        return 0;
    }
    if (tcsetattr(fd, TCSANOW, &attr) == -1) {
        perror("initserial(): tcsetattr()");
        return 0;
    }
    return fd;
}


int setRTS(int fd, int level)
{
    int status;

    if (ioctl(fd, TIOCMGET, &status) == -1) {
        perror("setRTS(): TIOCMGET");
        return 0;
    }
    if (level)
        status |= TIOCM_RTS;
    else
        status &= ~TIOCM_RTS;
    if (ioctl(fd, TIOCMSET, &status) == -1) {
        perror("setRTS(): TIOCMSET");
        return 0;
    }
    return 1;
}


int main()
{
    int fd;
    char *serialdev = "/dev/ttyUSB0";

    fd = openserial(serialdev);
    if (!fd) {
        fprintf(stderr, "Error while initializing %s.\n", serialdev);
        return 1;
    }

    setRTS(fd,1);
    usleep(1);      
    setRTS(fd, 0);

    closeserial(fd);
    return 0;
}