Connect to cisco router with c++ via serial interface

Question

I want to connect to Cisco router from my c++ application. Need it in order to get interface status. My linux station (Ubuntu) and the router connected via serial interface.

connected from puty or minicom or Console Connections work.

for example:

root@test:/etc/minicom# cu -l /dev/ttyS0 -s 9600
Connected.

Router#show int summary

 *: interface is up
 IHQ: pkts in input hold queue     IQD: pkts dropped from input queue
 OHQ: pkts in output hold queue    OQD: pkts dropped from output queue
 RXBS: rx rate (bits/sec)          RXPS: rx rate (pkts/sec)
 TXBS: tx rate (bits/sec)          TXPS: tx rate (pkts/sec)
 TRTL: throttle count

Now i tried to do the same with C++ (or C) , but read hang.

My c code:

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <unistd.h>
#include <iostream>
#include<stdio.h>
#include<sys/ioctl.h>
#include<unistd.h>
#include<fcntl.h>
using namespace std;
int fd1;
int fd2;
char *buff, *buffer, *bufptr;
int wr, rd, nbytes, tries;

int configure_port(int fd)      // configure the port
        {
    struct termios port_settings;     // structure to store the port settings in
    bzero(&port_settings, sizeof(port_settings));
    cfsetispeed(&port_settings, B9600);    // set baud rates
    cfsetospeed(&port_settings, B9600);

    port_settings.c_cflag &= ~PARENB;    // set no parity, stop bits, data bits
    port_settings.c_cflag &= ~CSTOPB;
    port_settings.c_cflag &= ~CSIZE;
    port_settings.c_cflag |= CS8;

    tcsetattr(fd, TCSANOW, &port_settings);    // apply the settings to the port
    return (fd);

}
int main() {
    fd1 = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd1 == -1) {
        perror("open_port: Unable to open /dev/ttyS0 – ");
    } else {
        fcntl(fd1, F_SETFL, 0);
    }
    printf("Port 1 has been sucessfully opened and %d is the file description\n",fd1);
    configure_port(fd1);

wr = write(fd1, "\r", 1);
cout << " wr status " << wr << endl;
wr = write(fd1, "\r", 1);
cout << " wr  status " << wr << endl;
wr = write(fd1, "ena\r", 4);
cout << " wr status " << wr << endl;
wr = write(fd1, "show int sum\r", 13);
cout << " wr status " << wr << endl;
rd = read(fd1, buff, 50);
cout << " rd status " << rd << endl;
cout << rd << endl;
    return 0;
}

Have you checked `port_settings` after setting it up? I notice it isn't initialized to zero ... — Useless, Oct 29 '12 at 16:22
My first suggestion was going to be "try cu" (Linux) or "hyperterminal" (Windows). But you've done that - the RS232 connection is OK. Q: Have you tried initializing "port_settings" to zero? — paulsm4, Oct 29 '12 at 16:23
@paulsm4 i am new to this , can you please explain 'port_settings' to 0 ? — Avihai Marchiano, Oct 29 '12 at 16:25
@Useless if you mean to add bzero(&port_settings, sizeof(port_settings)); than this cause to read hang . without it read failed — Avihai Marchiano, Oct 29 '12 at 16:35
OK, so first: when read failed, what was the error? Second, if read hangs, presumably it's at least waiting successfully for data ... and I assume the correct line ending is definitely `\r`? You could `strace` both cu and your process, to compare _exactly_ what they're both writing to `/dev/ttyS0` ... — Useless, Oct 29 '12 at 16:41

score 0 · Answer 1 · answered Oct 29 '12 at 16:40

0

You aren't zeroing your port_settings struct first before modifying it. That's surely a bug, though it may not be the source of your problems. Have you tried building one of the dozens of "termios sample programs" available on the intnernet for comparison?

answered Oct 29 '12 at 16:40

Andy Ross

11,699
1
34
31

I tried to zeroieng but than the read is hang. i copy my example from the internet. i also tried this example - http://stackoverflow.com/questions/6947413/how-to-open-read-and-write-from-serial-port-in-c , but read still hang – Avihai Marchiano Oct 29 '12 at 16:47
You can't find *any* working examples with your serial port? That seems very strange. Try running `stty < /dev/ttyS0` when minicom is running and when your (hanging) program is running and see what the difference is. Also: please prune your example program to the minimal subset. I see not reason to be clearing the file descriptor flags with `fcntl`, using non-blocking I/O or using NOCTTY for a process to be run interactively... – Andy Ross Oct 29 '12 at 16:53

score 0 · Accepted Answer · answered Oct 31 '12 at 09:07

This work - probably sleep was missing.

#include <stdio.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <termios.h>
#include <unistd.h>
#include <iostream>
#include<stdio.h>
#include<sys/ioctl.h>
#include<unistd.h>
#include<fcntl.h>

using namespace std;

int set_interface_attribs(int fd, int speed, int parity) {
    struct termios tty;
    memset(&tty, 0, sizeof tty);
    if (tcgetattr(fd, &tty) != 0) {
        printf("err");//error_message("error %d from tcgetattr", errno);
        return -1;
    }

    cfsetospeed(&tty, speed);
    cfsetispeed(&tty, speed);

    tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;     // 8-bit chars
    // disable IGNBRK for mismatched speed tests; otherwise receive break
    // as \000 chars
    tty.c_iflag &= ~IGNBRK;         // ignore break signal
    tty.c_lflag = 0;                // no signaling chars, no echo,
                                    // no canonical processing
    tty.c_oflag = 0;                // no remapping, no delays
    tty.c_cc[VMIN] = 0;            // read doesn't block
    tty.c_cc[VTIME] = 5;            // 0.5 seconds read timeout

    tty.c_iflag &= ~(IXON | IXOFF | IXANY); // shut off xon/xoff ctrl

    tty.c_cflag |= (CLOCAL | CREAD); // ignore modem controls,
                                     // enable reading
    tty.c_cflag &= ~(PARENB | PARODD);      // shut off parity
    tty.c_cflag |= parity;
    tty.c_cflag &= ~CSTOPB;
    tty.c_cflag &= ~CRTSCTS;

    if (tcsetattr(fd, TCSANOW, &tty) != 0) {
        printf("err");//error_message("error %d from tcsetattr", errno);
        return -1;
    }
    return 0;
}

void set_blocking(int fd, int should_block) {
    struct termios tty;
    memset(&tty, 0, sizeof tty);
    if (tcgetattr(fd, &tty) != 0) {
        printf("err");//error_message("error %d from tggetattr", errno);
        return;
    }

    tty.c_cc[VMIN] = should_block ? 1 : 0;
    tty.c_cc[VTIME] = 5;            // 0.5 seconds read timeout

    if (tcsetattr(fd, TCSANOW, &tty) != 0)
        printf("err");//error_message("error %d setting term attributes", errno);
}

int main(int argc, char **argv) {
    char *portname = "/dev/ttyS0";
    int fd = open (portname, O_RDWR | O_NOCTTY | O_SYNC);
    if (fd < 0) {
        printf("err");//error_message("error %d opening %s: %s", errno, portname,strerror(errno));
        return -1;
    }

    set_interface_attribs(fd, B9600, 0); // set speed to 115,200 bps, 8n1 (no parity)
    set_blocking(fd, 0);                // set no blocking
    write(fd, "\r", 1);           // send 7 character greeting
    write(fd, "\r", 1);
    usleep(100000);
    char buf[1000];
    write(fd, "ena\r", 4);
    memset(&buf, 0, sizeof buf);
    usleep(100000);
    write(fd, "show int sum\r", 15);
    sleep(1);
    memset(&buf, 0, sizeof buf);
    int n = read(fd, buf, sizeof buf); // read up to 100 characters if ready to read
    cout << " n " << n << endl;
    cout << " buf " << buf <<  endl;
    close(fd);
}

Relying on sleep or other delays to result in capturing a full reply is an unreliable implementation which could break if the connected devices replies more slowly some day. You want to read in a loop until you have received a full reply through the specified terminating character/condition, or use a read function which reads until such condition (or timeout or other fault). — Chris Stratton, Nov 03 '12 at 17:46
@ChrisStratton can you give a reference to " read with timeout " — Avihai Marchiano, Nov 03 '12 at 19:31
Look at select() or related syscalls as a means of implementing a data check with a timeout, and read only if they indicate data is available. Or you can put the port in non-blocking mode and poll it periodically (but beware that busy-waiting in a tight loop will hog a lot of CPU and reduce the performance of other tasks). You already seem to be setting up non-blocking I/O, so shortening the sleep and putting in a loop until a complete message is received would work - but beware of collecting the end of one message and the start of another in a single multi-byte read. — Chris Stratton, Nov 03 '12 at 19:37

score 0 · Answer 3 · answered Oct 31 '12 at 09:15

0

You should use SNMP to get interface status/statistics instead of connecting to serial console.

This is exact purpose what was SNMP designed for.

answered Oct 31 '12 at 09:15

rkosegi

14,165
5
50
83

The management control computer cannot have network connect with the router (security) , so need to connect with serial. – Avihai Marchiano Oct 31 '12 at 09:19

Connect to cisco router with c++ via serial interface

3 Answers3