Reading Serial Data From C (OSX /dev/tty)

Question

I am trying to read data from a bluetooth barcode scanner (KDC300) using C. Here is the code I have so far, and the program successfully establishes a bluetooth connection to the scanner, but when a barcode is scanned, no input is displayed on the screen (Eventually more will be done with the data, but we have to get it working first, right).

Here is the program:

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

int main (int argc, const char * argv[]) {

    // define vars
    int STOP = 0;
    //char buf[255];

    if(argv[1])
    {
        int fd = open("/dev/tty.KDC1", O_RDONLY);
        if(fd == -1)
        {
            printf("%s", strcat("Unable to open /dev/tty.", argv[1]));
        }

        int res;
        while(STOP == 0)
        {
            while((res = read(fd,buf,255)) == 0);
            {
                if(res > 0)
                {
                    buf[res]=0;
                    printf("%s:%d\n", buf, res);
                    if(buf[sizeof(buf)]=='\n') break;   
                }
            }
        }
    }

    return 0;
}

If anyone has any ideas, I am at a loss on this so far. If it is any help, I can run screen /dev/tty.KDC1 and any barcodes scanned on the scanner appear in the terminal, I just can't do anything with the data.

Jud

Answer 1

In your code

printf("%s", strcat("Unable to open /dev/tty.", argv[1]));

Why did you do that? It would be easier to do it this way:

printf("%s: Unable to open /dev/tty.KDC1", argv[0]); 

Why the parameter referencing to the command line?

res = read(fd,buf,255)

Why did you have buf declaration commented out above?

Answer 2

This line:

        while((res = read(fd,buf,255)) == 0);

Does not do what you think it does. That's a while loop with an empty body.

Answer 3

@tommieb75, the strcat statement was from the first "go" at the program, I took a variable from argv[1] and appended it to the /dev/tty.* so you could select which device you wanted to monitor.

I am not sure why I had commented out buf, probably stems from looking at the code too much / trying different approaches and forgetting where I was (not much of a C programmer, which is how I can get lost in 30 LOC).

@caf, Good catch on the extra semi-colon after the while loop, unfortunately, even after correcting it, the program doesn't behave correctly.

I am researching the problem further. I can verify (with osx packetlogger) that the computer is getting the data, but the but the buffer never has any data placed in it.

-Jud

---------------Edit--------------

I solved the problem after a little trial and error. Adding the following code to setup the serial connection solved everything:

struct termios theTermios;

memset(&theTermios, 0, sizeof(struct termios));
cfmakeraw(&theTermios);
cfsetspeed(&theTermios, 115200);

theTermios.c_cflag = CREAD | CLOCAL;     // turn on READ
theTermios.c_cflag |= CS8;
theTermios.c_cc[VMIN] = 0;
theTermios.c_cc[VTIME] = 10;     // 1 sec timeout
ioctl(fileDescriptor, TIOCSETA, &theTermios);

Thanks to the other answers for getting me to this point.