CODEWITHSUNDEEP
c++windowsqtftdiqtserialport
user257980
user257980

Reputation: 1089

qt 5.2 serial port write issues with windows 7

We are using FTDI serial port CHIP in our hardware. Now we have working code in Linux and we moved to windows 7. We get some weird problems.

The Problem: We can't write data to Serial Port without running other console application which do this:

 serial.setPortName("COM3");
        if (serial.open(QIODevice::ReadWrite)) {
            bool success = serial.setBaudRate(QSerialPort::Baud9600) &
            serial.setStopBits(QSerialPort::OneStop) &
            serial.setDataBits(QSerialPort::Data8) &
            serial.setParity(QSerialPort::NoParity) &
            serial.setFlowControl(QSerialPort::NoFlowControl);
            qDebug() << "Connected to usb device: " << (success ? "OK" : "FAIL");

           while(true) {
                if(serial.waitForReadyRead(-1)) {
                    QByteArray out = serial.readAll();
                    for(int i=0; i< out.length(); i++) {
                        qDebug() << (int) out[i];
                    }
                }
            }
            serial.close();

So its just loop with read all. Hardware dosen't send anything, so read is just infinity loop. After closing and running our write program it runs correctly.

char* input;
input = new char[size+3];
QByteArray bytearr;

for(int i=0;i<size+2;i++) {
    input[i] = (char) package[i];
    bytearr.append((unsigned char) package[i]);
}


QString serialPortName = "COM3";
QSerialPort serialPort;
serialPort.setPortName(serialPortName);
serialPort.open(QIODevice::ReadWrite);
serialPort.write(bytearr);
serialPort.flush();
serialPort.close();

After running read everything works, but without read all, it wont work. What are we doing wrong? Thanks.

Upvotes: 3

Views: 3494

Answers (2)

Alexej S.
Alexej S.

Reputation: 41

We had similar problem in our application with a board with FTDI chip. We tried to write bytes with 19200 baud/sec, had though in real about 1200 baud/sec (seen using oscilloscope). The problem was closing the serial port right after writing a byte. Just waiting using QThread::msleep(5) before closing the port helped. It seems, that the device gets a reset or something during close operation and latest bytes are sent with false baudrate and other parameters.

Upvotes: 2

Oldfart
Oldfart

Reputation: 6259

I found out that the QT serial port SW requires you to process QT events in order to work. Putting a qApp->processEvents() in the loop before the read made it work for me.

(QT 4.8.5 on Windows-7)

Upvotes: 1

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