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Date:      Sun, 20 Sep 2009 01:36:19 -0400
From:      Pierre-Luc Drouin <>
Subject:   Newbie question about ASYNC communication with FTDI-based device (via uftdi)
Message-ID:  <>

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I'm trying to hack the code of tbancontrol, a linux tool used to control 
t-balancer fan controllers that use FTDI FT232BL chips. It seems to be 
working fine on linux, but when I try to use it on FreeBSD, I noticed 
that read calls fail with "Interruted system call". It seems there is 
something wrong with the SIGIO signal since it is generated as soon as 
tcsetattr is called. I guess there must be something wrong with either 
the way the device is opened or (more likely) the way the descriptor is 
configured, but I have very little experience with serial 
communication... Here is the main lines of the code related to 

tban->port = open("/dev/ttyU0", O_RDWR | O_NOCTTY | O_NONBLOCK);
saio.sa_handler = tban_signal_handler_IO;
result = sigemptyset(&saio.sa_mask);
saio.sa_flags = 0;
result = sigaction(SIGIO, &saio, NULL);
result = fcntl(tban->port, F_SETFL, FASYNC);
tcgetattr(tban->port, &(tban->oldtio));
memcpy(&newtio,&tban->oldtio,sizeof(struct termios)); /*I added this 
line to avoid the error EINVAL when calling tcsetattr below. This is 
probably not enough to set all flags properly :S */

newtio.c_cflag = intToBaud(tban->baudrate)  /*baudrate is 19200*/
    | intToDataBits(tban->databits) /*databits is 8*/
    | intToStopBits(tban->stopBits) /*stopBits is 0*/
    | CLOCAL
    | CREAD;
  newtio.c_iflag     = IGNPAR;
  newtio.c_oflag     = 0;
  newtio.c_lflag     = 0;
  newtio.c_cc[VMIN]  = 1;
  newtio.c_cc[VTIME] = 0;
result = tcsetattr(tban->port, TCSANOW, &newtio);
/*SIGIO is generated (?)*/
result = write(tban->port, sndBuf, cmdLen); /*request device status*/
/*Initialize data availability flag to false*/
/*sleep 1 second*/
/*SIGIO is generated */
bytesread = read(tban->port, local_buf, sizeof(local_buf));
/*bytesread is -1, EINTR is generated*/

So does anybody know what could be wrong in this code?

Thanks a lot!

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