Problem writing on serial device

maus · 10-09-2009, 11:13 AM

Hi,

I'm writing a program which reads and writes data on the serial device.

Reading works fine. But with writing I'm struggling.

Here is my code reduced to the minimum:

Code:

	//----< Open serial device >----------------------------------
	int fileDescriptor;
	fileDescriptor = open(devTTY, O_RDWR | O_NOCTTY);
	
	if (fileDescriptor == -1) {
		perror("Error while opening serial interface occurred!");
		return -99;
	}

	// set new parameters to the serial device
	struct termios newtio;
	tcgetattr(fileDescriptor, &oldTio);
	// flush it before restore it.
	bzero(&newtio, sizeof(newtio));
	//	newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
	

	// canonical disable -> RAW input
	newtio.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
	newtio.c_cflag = BAUDRATE | CRTSCTS	| CLOCAL | CREAD;

	// When the OPOST option is disabled, all other option bits in  c_oflag are ignored.

	//	newtio.c_oflag &= ~OPOST;
	// newtio.c_oflag |= OPOST;
	newtio.c_oflag = 0;

	secs vor next char during burst
	
	tcflush(fileDescriptor, TCIFLUSH);
	if (tcsetattr(fileDescriptor, TCSANOW, &newtio)) {
		perror("could not set the serial settings!");
		return -99;
	}

	
	//----  Open serial device ----------------------------------
	char acki[32] = { "test test\n\0" };


// finally writing
if (write(fd, acki, strlen(acki)) != strlen(acki)) {
			perror("can't write);
		}

I'm testing my program with a Nullmodem-Cable plugged in to /dev/ttyS0 and /dev/ttyUSB0

One end is the program by me, at the other end I use Screen. I checked the setup by running Screen on both ends and writing messages to each other end.

I guess the error is somewhere in the Serial-Settings. Any suggestions? Thanks

smeezekitty · 10-09-2009, 01:18 PM

Quote:

I guess the error is somewhere in the Serial-Settings. Any suggestions? Thanks

clarify

michaelk · 10-09-2009, 01:51 PM

Without seeing all of your code it is difficult to provide help. What you posted does not look like it will compile without errors. Homework?

One error that pops out:

Code:

fileDescriptor = open(devTTY, O_RDWR | O_NOCTTY);
vs
write(fd, acki, strlen(acki))

salasi · 10-09-2009, 05:18 PM

Err, but what does happen? Do you get nothing, lost characters or are all you characters corrupt?

And you cable, what connections have you made in addition to txdata and rxdata? And are you trying to use software or hardware flow control?

maus · 10-10-2009, 06:06 AM

Quote:

Originally Posted by michaelk

Without seeing all of your code it is difficult to provide help. What you posted does not look like it will compile without errors. Homework?

One error that pops out:

Code:

fileDescriptor = open(devTTY, O_RDWR | O_NOCTTY);
vs
write(fd, acki, strlen(acki))

Sorry, I merged the given code from two functions into one. Of course fd is the valid and open filedescriptor. Anyway, writing works just fine, and returns the number of written bytes. No homework. I'm trying to interrogate my solar power converter.

Again, I'm fine while reading from the serial device without any problems. I just have the impression that in case of writing nothing comes out.

Quote:

Originally Posted by salasi

Err, but what does happen? Do you get nothing, lost characters or are all you characters corrupt?

And you cable, what connections have you made in addition to txdata and rxdata? And are you trying to use software or hardware flow control?

I'm loosing all characters which I try to write out.
I'm using a ordinary Null-Modem cable which worked fine during a test with a Minicom or Screen apps at both ends.

I guess I'm using the standard software flow control.

michaelk · 10-10-2009, 06:30 AM

If you can read then the serial port parameters are ok and so you should be able to transmit characters as well.
If nothing comes out then you still might have errors in your code which is why I asked if you would post your entire program.

maus · 10-14-2009, 05:46 PM

Hi,

I was wrong with the CRTSCTS Option. There is no HW flow control. Now I'm able to write.

Thanks for your Support.