Question

I want to read data from my serial port on Linux with C/C++ code.
As I can still read from this serial port with GtkTerm and even with cat /dev/ttyUSB0, this is not a hardware / driver problem.

It seems that the serial port is not initiated correctly as reading do works after the use a program like gtkterm.

Here is the code I use to init the serial port (seconde version) :

UbiDriver::UbiDriver(const std::string &ttyPort)
{
    // Doc : http://www.easysw.com/~mike/serial/serial.html#2_4

    m_serialHandle = open(ttyPort.c_str(), O_RDWR | O_NOCTTY | O_NDELAY); // Open perif
    if(m_serialHandle < 0)
    {
        MY_THROW("Impossible d'ouvrir le port '" << ttyPort << "' !\nerrno = " << errno);
    }

    // Conf
    //if(fcntl(m_serialHandle, F_SETFL, 0) == -1) // lecture en mode bloquant
    if(fcntl(m_serialHandle, F_SETFL, O_NONBLOCK) == -1) // lecture en mode non bloquant
    {
        MY_THROW("fcntl failed !\nerrno = " << errno);
    }

    struct termios options;
    tcgetattr(m_serialHandle, &options); // Init struct avec la conf actuelle

    cfsetispeed(&options, B9600); // In speed
    cfsetospeed(&options, B9600); // Output speed

    options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
    options.c_cflag |= (CLOCAL | CREAD); // Enable the receiver and set local mode...
    options.c_cflag &= ~PARENB; // Desactive bit de parité
    options.c_cflag &= ~CSTOPB; // Désactive 2 stop bits -> Active 1 stop bits
    options.c_cflag &= ~CSIZE; // Désactive le bit "CSIZE"
    options.c_cflag |= CS8; // Communication sur 8 bits

    options.c_oflag &= ~OPOST; // Raw output is selected by resetting the OPOST option in the c_oflag member:

    // Application de la conf
    if(tcsetattr(m_serialHandle, TCSAFLUSH, &options) == -1) // Vidage buffer & application immédiate
    {
        MY_THROW("tcsetattr failed !\nerrno = " << errno);
    }
}

And to read data from the port

std::string UbiDriver::GetAnswer()
{
    const int buffSize = 1024;
    char buffer[buffSize] = {'\0'};
    int count = 0;
    std::string wholeAnswer = "";

    int noDataTime = 0;

    while(noDataTime < 2) // Tant qu'il y a des données à lire
    {
        count = read(m_serialHandle, buffer, buffSize - 1);
        if(count == -1)
        {
            MY_THROW("Impossible de lire sur le port serie. Verifiez la connexion avec l'imprimante !")
        }

        if(count > 0)
        {
            noDataTime = 0;

            buffer[count] = '\0';
            for(int i = 0; i < count; i++)
            {
                buffer[i] &= ~128; // Supression du premier 1 du binaire
            }

            wholeAnswer += std::string(buffer);
            std::cout << count << std::endl;
        }
        else
        {
            noDataTime++;
            usleep(100000);
        }
    }

    cerr << "----------- Answer -----------" << endl;
    cerr << "Size = " << wholeAnswer.size() << endl;
    cerr << wholeAnswer << endl;

    return wholeAnswer;
    return std::string("");
}

Note: this code is a second version completed with your comments.

Answer 1

I opened the gtkterm source code and I finally found a solution : in fact, you need to override the terminos structure (and yes, you should not have to do it normally).

If someone finds a better solution, feel free to post it. In the meantime, here is the working code, with english comments :

To open the serial port :

// Doc : http://www.easysw.com/~mike/serial/serial.html#2_4

m_serialHandle = open(ttyPort.c_str(), O_RDWR | O_NOCTTY | O_NDELAY); // Open serial port
if(m_serialHandle < 0)
{
    MY_THROW("Impossible d'ouvrir le port '" << ttyPort << "' !\nerrno = " << errno);
}

// Read mode
//if(fcntl(m_serialHandle, F_SETFL, 0) == -1) // Blocking read
if(fcntl(m_serialHandle, F_SETFL, O_NONBLOCK) == -1) // Non-blocking read
{
    MY_THROW("fcntl failed !\nerrno = " << errno);
}

// Get current terminos configuration
struct termios options;
tcgetattr(m_serialHandle, &options);

// Force termios values (should not be needed, but is)
options.c_cflag = B9600;
options.c_oflag = 0;
options.c_lflag = 0;
options.c_iflag = IGNPAR | IGNBRK;
options.c_cc[VTIME] = 0;
options.c_cc[VMIN] = 1;

// Set data rate
cfsetispeed(&options, B9600); // In speed
cfsetospeed(&options, B9600); // Output speed

// Set communication flags
options.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
options.c_cflag |= (CLOCAL | CREAD); // Enable the receiver and set local mode...
options.c_cflag &= ~PARENB; // Desactive bit de parité
options.c_cflag &= ~CSTOPB; // Désactive 2 stop bits -> Active 1 stop bits
options.c_cflag &= ~CSIZE; // Désactive le bit "CSIZE"
options.c_cflag |= CS8; // Communication sur 8 bits

options.c_oflag &= ~OPOST; // Raw output is selected by resetting the OPOST option in the c_oflag member:

// Disable flow control
options.c_iflag &= ~(IXON | IXOFF);

// Apply
if(tcsetattr(m_serialHandle, TCSANOW, &options) == -1) // Vidage buffer & application immédiate
{
    MY_THROW("tcsetattr failed !\nerrno = " << errno);
}

// Empty buffers
tcflush(m_serialHandle, TCIOFLUSH);

To read (non-blocking)

const int buffSize = 1024;
char buffer[buffSize] = {'\0'};
int count = 0;
std::string wholeAnswer = "";

int noDataTime = 0;

while(noDataTime < 3) // while there is data to be read
{
    count = read(m_serialHandle, buffer, buffSize - 1);
    // May fail in NON-BLOCKING mode if there is nothing to be read
    /*if(count == -1)
    {
        MY_THROW("Impossible de lire sur le port serie. Verifiez la connexion avec l'imprimante !")
    }*/

    if(count > 0)
    {
        noDataTime = 0;

        buffer[count] = '\0';
        /*for(int i = 0; i < count; i++)
        {
            buffer[i] &= ~128; // Delete first binary bit. Could be useful for 7 bit communication, if the first bit is set to 1
        }*/

        wholeAnswer += std::string(buffer);
    }
    else
    {
        noDataTime++;
        usleep(100000);
    }
}

if(!wholeAnswer.empty())
{
    cerr << "----------- Answer -----------" << endl;
    cerr << "Size = " << wholeAnswer.size() << endl;
    cerr << wholeAnswer << endl;
}

return wholeAnswer;