I am trying to communicate with a device by using a serial port and I have encountered a problem - with every library I have tried using so far (serial, Qextserialport, boost) it is the same. What happens is that I can send commands but I cannot receive any data.

I know that the device works properly because the same code executed as Qt project, without ROS, causes the device to send a response and I can observe this response, either in Qt by port->read (or similar command), or in terminal such as cutecom. While running a ROS program, there is no output. However I am sure the commands are correct (I can for example send a command to change digital outputs of my device and confirm in cutecom that they have changed).

Hence my question - does serial port communication work in a different way in these two examples (Qt and ROS)? Can ROS be blocking the reading from the port in some way? Maybe should I use longer timeouts?

Here is my code:

int main(int argc, char **argv){

ros::init(argc,argv,"device");
ros::Time::init();
ros::Rate loop_rate(1);

QextSerialPort *port;
PortSettings settings = {BAUD57600, DATA_8, PAR_NONE, STOP_1, FLOW_OFF, 10};

port = new QextSerialPort("/dev/ttyACM0", settings, QextSerialPort::Polling);

if(port->open(QIODevice::ReadWrite) == true)
{
    qDebug() << "OK";
}

while(ros::ok())
{
    commandCnt = 0;
    commandArray[commandCnt++] = NF_COMMAND_ReadDigitalInputs; // this is my command array 

    txCnt = NF_MakeCommandFrame(&NFComBuf, txBuf, commandArray, commandCnt, 48); // command frame

    if(port->write((const char*)txBuf, txCnt))
    qDebug() << "Commands sent";

    ros::spinOnce();
    loop_rate.sleep();
}}

I would be greatly appreciated if you could give me a hint where the problem can be.