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 th

Answer 1

Here is the best info I've found.

The C program on there using termios worked just by adding

#include<string.h>

And changing the baudrate to match my needs.

Answer 2

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 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.

Answer 4

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.