On Wed, 5 May 2010, Manfred Gruber wrote:
> 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 controller. My C code works
> without problems on ttyS0 but with the usb-to-serial adapter (I tried
> tree defferent chipsets pl2303, ch341-uart and FT232RL) it just sends
> but can't read from the controller.
What happens if you use your program to communicate with another
computer running minicom instead of with the PIC-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 what the problem could be?
>
> Manfred
>
> Im working on Ubuntu 9.10, Kernel 2.6.31-21
>
>
> here is my code:
> =====================================================
> 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));
Instead of using bzero, you should copy oldtio into newtio. By setting
everything to 0, you may be messing up something that is essential.
> 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);
> }
Alan Stern
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