connect to ttyUSB with C/C++

[korlans]

Hi,

on ubuntu I try to access a PIC-controler via the ttyUSB0. I send a few command bytes and get the status from the controler. My C code works without problems on ttyS0 but with the usb-to-serial adapter (I tried two with defferent chipsets pl2303 + ch341-uart) it just sends but can't read from the controller.
With minicom I can communicate with an other computer without problems but in my code there must be something wrong for the ttyUSB.

Any ideas?

Here my code for the termios configuration:

struct termios oldtio,newtio;

extern "C" HANDLE SioOpen(char *name, unsigned int baudrate)
{
BOOL RetStat;
HANDLE ComHandle;
DWORD winrate;

//Open COM port as a file
printf("Opening %s\n",name);
ComHandle = open(name, O_RDWR) | O_NOCTTY);

	if (ComHandle < 0)
		{
        printf("%s failed to open\n",name);
        perror(name); 
    	}

    switch (baudrate) {
		case 9600: 	winrate = B9600; break;
		case 19200: 	winrate = B19200; break;
		case 38400: 	winrate = B38400; break;
		case 57600: 	winrate = B57600; break;
		case 115200: 	winrate = B115200; break;
    	default:		printf("Baud rate not supported - using default of 19200\n");
    					winrate = B19200;
    	}
    //printf("tcgetattr(ComHandle,&oldtio)\n");

    tcgetattr(ComHandle,&oldtio); // save current port settings

    bzero(&newtio, sizeof(newtio));

    newtio.c_cflag = winrate | CS8 | CLOCAL | CREAD;
    newtio.c_iflag = IGNPAR;
    newtio.c_oflag = 0;

    // set input mode (non-canonical, no echo,...)
    newtio.c_lflag = 0;

    // Wait block for 100ms, then timeout
    newtio.c_cc[VTIME]    = 1;   // inter-character timer unused 
    newtio.c_cc[VMIN]     = 0;   // blocking read until 1 chars received 

    //tcflush(ComHandle, TCIFLUSH);
    tcflush(ComHandle, TCIOFLUSH);
    //printf("tcsetattr(ComHandle,TCSANOW,&newtio)\n");
    RetStat = tcsetattr(ComHandle,TCSANOW,&newtio);

	if (RetStat < 0)
    	{
    	printf("Failed to set COMM configuration\n");
        //break;
        }
//printf("Setup complete, returning file handle.\n"); 
return(ComHandle);
}

[BrianMicek]

Sorry for the late response, I had this same problem months later. My problem occurs 2/3 of the time. For reasons unknown, if you open(2) your tty non blocking then select(2) on your read(2), things will probably work. I suppose its a driver problem. I observed minicom always worked and strace(1)d it and compared the output with my output. I'm really surprised this problem has been around this long.