manually controlling RTS/CTS

pappsynz · 05-24-2005, 09:27 AM

Hi there,

I'm trying to write a piece of software to test a UART driver and chip that I had been playing with. The chip is on a PCI card, and I have a cross over cable between the serial port on the card to the 'COM0' serial port on the motherboard. I'm wanting to test the Hardware Flow Control, whilst having the current setup and so am hoping to be able to set RTS through command line calls using maybe stty?

On Unix I have found that stty has some hardware flow control modes such as [-]rtsxoff and [-]ctsxon... however Linux doesn't look to have these. Is there any equivalent??

I'm using Linux 2.6.10, and a Red Hat distro. Any tips would be much appreciated, even if it means a change of tack.

Thanks
Ben

Hko · 05-24-2005, 10:37 AM

Quote:

Originally posted by pappsynz
On Unix I have found that stty has some hardware flow control modes such as [-]rtsxoff and [-]ctsxon... however Linux doesn't look to have these. Is there any equivalent??

GNU/Linux's stty does have these:

`crtscts'
Enable RTS/CTS flow control. Non-POSIX. May be negated.
`ixon'
Enable XON/XOFF flow control (that is, `CTRL-S'/`CTRL-Q'). May be
negated.

Is this what you're looking for?

See "info coreutils stty" for more.

pappsynz · 05-24-2005, 10:50 AM

Hey there ;-)

Actually I've already got this set, however as far as I can tell this (crtscts) only turns on the hardware flow control, I cant use it to stop and start data flow manually.

As I cannot set up a test network to try and force the hardware flow control to have to toggle RTS etc..., I am hoping to be able to write a few lines of code that will set RTS to 0, pause and then reset RTS to 1 as a way of forcing the driver for the other UART to use its flow control mechanism.

Hko · 05-24-2005, 11:26 AM

Quote:

Originally posted by pappsynz
I am hoping to be able to write a few lines of code that will set RTS to 0, pause and then reset RTS to 1 [...]

I still had some code around that's is able to do that.
I changed it to do what you described above.

Code:

#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/ttyS0";

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

    setRTS(fd, 0);
    sleep(1);       /* pause 1 second */
    setRTS(fd, 1);

    closeserial(fd);
    return 0;
}

If you saved the code above as "bumpRTS.c" you can compile it the easiest way by entering:

Code:

make bumpRTS

or, more sophisticated, with:

Code:

gcc -Wall -pedantic -O2 -o bumpRTS bumpRTS.c

Either way, the executable will be stored as "bumpRTS.c" in the same directory.
Hope this does what you need.

pappsynz · 05-25-2005, 04:55 AM

Hi Hko,

Thanks a million for the help! The ioctl is exactly what I was looking for.

Have made the necessary adjustments and additions to my code and it great.

Thanks again,

pappsynz