[Gumstix-users] Writing to Serial port

[Joost M. <joo...@ho...>]

Hi All,

I am trying to write something to the serial port of the gumstix (the serial 
port is located on the tweener expansion board). First I connected the 
gumstix to my PC via serial. When doing this I listen on the PC side what is 
written to serial port on the Gumstix side. This seems to work correctly 
(since I am writing bytes, some characters do not appear on the screen). 
However, when connecting the device I want to control to the Gumstix it does 
not work correctly. Now is the case that for the device I want to control a 
specific protocol is needed. The key element in this protocol is to switch 
from "space" to "mark" parity and vice-versa. Please see the code below 
where I do the setup in the first snippet, and I do the switching of parity 
in the second snippet.

My feeling says that something goes wrong when cross-compiling the code to 
the Gumstix hardware.
Since the same code is working fine on my PC Linux machine (i.e. I can 
successfully control the device). Does anyone have experience with this? Or 
can anyone give me a clue were to look? Maybe someone experienced problems 
with "termios.h" before?

Thanks a lot in advance.


Kind regards,

Joost Meijles
PS. Reading from the serial port goes fine.

================SETUP============
int fd = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NDELAY);
	tcflush(fd, TCIOFLUSH);
	debug("serial port open");
	//configure the serial port
	struct termios options;

	if(tcgetattr(fd, &options) < 0)		// READ SETTINGS
	{
		debug("error getting serial port configuration");
	}

	cfmakeraw(&options);
	cfsetospeed(&options, B115200);			// SET SPEED
	cfsetispeed(&options, B115200);

	options.c_iflag &= ~CLOCAL;				// Set ...
	options.c_cflag |= CLOCAL;
	options.c_iflag &= ~CREAD;
	options.c_cflag |= CREAD;

	options.c_iflag &= ~CSTOPB;				// SET STOPBITS

	options.c_iflag &= ~PARENB;				// SET PARITY BITS
	options.c_iflag &= ~PARODD;

	// Odd
	options.c_cflag |= PARENB;
	options.c_cflag |= PARODD;


	options.c_iflag &= ~CS5;				// SET DATABITS
	options.c_iflag &= ~CS6;
	options.c_iflag &= ~CS7;
	options.c_iflag &= ~CS8;

	// 8 databits
	options.c_cflag |= CS8;

	options.c_cflag &= ~CRTSCTS;			// SET HARDWARE FLOW CONTROL to none


	if(tcsetattr(fd, TCSANOW, &options) < 0)	// WRITE SETTINGS
	{
		debug("error writing configuration to serial port");
	}
===========================================

===============SWITCH=====================
//switch the parity for writing
	tcgetattr(fd, &options);//get the configuration
	options.c_cflag &= ~PARENB;
	options.c_cflag &= ~PARODD;
	options.c_cflag |= PARENB | 010000000000;
	options.c_cflag &= ~PARODD;
	if(tcsetattr(fd, TCSAFLUSH, &options) < 0) {//set the configuration
		debug("error writing configuration to serial port");
	}
============================================

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