[Gumstix-users] Serial Driver, BTUART, RTS is always driven low and CTS is never seen

[rketcham <Ric...@gm...>]

Hello,

I'm trying to employ RTS and CTS through the BTUART. Unfortunately, it looks
like something is amiss. When I write to the serial port, the RTS line is
always brought low regardless if RTSCTS has been set or not.  Also, I don't
have to be sending anything for RTS to be driven low; I just have to open
the port. Is this normal operation? I wouldn't think so... 

After observing these two features I tried communicating with my external
device anyway. The external device would see RTS driven low and respond with
driving CTS low but the serial driver never sees CTS change and so gets hung
up waiting to send the data. I tried doing this myself by disabling RTSCTS,
driving RTS low manually (ioctl) and waiting for CTS to be driven low in a
while loop.  However, the ioctl never returns with CTS as other than 0. 

Is there a known problem with the serial driver that causes this? Is there a
simple way for me to fix this without getting into driver programming? If
not, do you have any advice on what I need to edit?

My buildroot revision is 1633. I have RTS on the Gumstix connected to RTS on
my external device. I also have CTS on the Gumstix connected to CTS on my
external device.

Thanks,
Rich

Here is my code for setting up the serial port

	_fileDescriptor = open(devicePath.c_str(), O_RDWR | O_NOCTTY);//Open the
port

	if (_fileDescriptor== -1) //Opening of port failed
	{
		fprintf(stderr,"open_port: Unable to open %s.\n", devicePath.c_str());
	}

	int databits = 8;//Number of data bytes in packet.

	//Initialize to the default value.
	int BAUD = B115200; //115200 bits per sec
	int DATABITS = CS8;//8 data bits per packet
	int STOPBITS = ~CSTOPB; //1 stop bit
	int PARITY = 0; // 0 parity
	int PARITYON = ~PARENB;//Parity is not enabled.
	int status = 0; //Assume the port is set with the new comm settings.

	//Get the current options for the port...
	tcgetattr(_fileDescriptor, &_options);

	//Sellect the baud rate.
	switch(baudRate)
	{
		 //115200: //Most likely according to the SDK.
		case baudRate_115200: BAUD = B115200; break;
		case baudRate_2400:   BAUD = B2400;   break;
		case baudRate_4800:   BAUD = B4800;   break;
		case baudRate_9600:   BAUD = B9600;   break;
		case baudRate_19200:  BAUD = B19200;  break;
		case baudRate_38400:  BAUD = B38400;  break;
		case baudRate_57600:  BAUD = B57600;  break;
		default:              BAUD = B115200; //Default to the baud in the SDK
	}
	cfsetospeed(&_options, BAUD);
	cfsetispeed(&_options, BAUD);

	//Assign the number of data bits.
	switch(databits)
	{
		case 8:	 DATABITS = CS8; break;
		case 7:  DATABITS = CS7; break;
		case 6:  DATABITS = CS6; break; //Not likely but available.
		case 5:  DATABITS = CS5; break; //Not likely but available.
		default: DATABITS = CS8; //Default to SDK value
	}

	_options.c_cflag &= ~CSIZE; /* Mask the character size bits */
    _options.c_cflag |= DATABITS;/* Select 8 data bits */

	//Assign the number of stop bits.
	switch(stopBits)
	{
		case stopBits__1_0:
			STOPBITS = ~CSTOPB;//Not 2 --> 1 stop bit
			_options.c_cflag &= STOPBITS;// stop bits
			break;

		case stopBits__2_0:
			STOPBITS = CSTOPB; //2 stop bits
			_options.c_cflag |= STOPBITS;// stop bits
			break;

		default:
			STOPBITS = ~CSTOPB; //Default to SDK value
			_options.c_cflag &= STOPBITS;// stop bits
	}

	 //Set parity.
	switch(parity)
	{
		case parity_none: //No parity.
			PARITYON = ~PARENB;
			_options.c_cflag &=PARITYON;
			PARITY = 0;	//Doesn't matter
			break;

		case parity_odd://Odd parity.
			PARITYON = PARENB;
			_options.c_cflag |=PARITYON;
			PARITY = PARODD;
			_options.c_cflag |= PARITY;//Odd Parity
			break;

		case parity_even://Even parity.
			PARITYON = PARENB;
			_options.c_cflag |=PARITYON;
			PARITY = ~PARODD;
			_options.c_cflag &= PARITY;//Even Parity
			break;

		default: //Default setting doesn't have parity checking.
			PARITYON = ~PARENB;//No parity
			_options.c_cflag &=PARITYON;
			PARITY = 0;//Doesn't matter
	}

	//set for non-canonical (raw processing, no echo, etc.)
   	_options.c_iflag = IGNPAR; // ignore parity check close_port(int
   	_options.c_oflag = 0; // raw output
	_options.c_lflag = 0; // raw input

	//Time-Outs -- won't work with NDELAY option in the call to open
	_options.c_cc[VMIN]  = 0;   // block reading until RX x characers. If x =
0, it is non-blocking.
	_options.c_cc[VTIME] = 1;   // Inter-Character Timer -- i.e. timeout= x*.1
s

	//Set local mode and enable the receiver
	_options.c_cflag |= (CLOCAL | CREAD);
	_options.c_cflag |= CRTSCTS; //Turn on flow control
	//_options.c_cflag &= ~CRTSCTS; //Turn off flow control
	//Purge serial port buffers
	Purge();

	//Set the new options for the port...
	status=tcsetattr(_fileDescriptor, TCSANOW, &_options);

	if (status != 0) //For error message
    	printf("Setting com port didn't work!\n");
	//else
    	//printf("Setting com port did work!\n");

	//Get the current options for theRead port...
	tcgetattr(_fileDescriptor, &_options);

	//Purge serial port buffers
	Purge();







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