CODEWITHSUNDEEP
c++qtuart
cqRinO
cqRinO

Reputation: 23

UART doesn't receive all sent values in Qt

I'm triying to send data from a PSoc via UART to my PC where a want to store data with Qt. The PSoc sends 3 bytes of data. Theses 3 bytes are repeatet with a frequency of 2.5Hz. When I check the signals with my oscilloscope everything is fine. When I receive the data with the software HTerm also everything is as expected. When I use my code written in c++ with Qt I get the problem that not all data are received in Qt, only one third is in the memory. I expected that the signal readyRead is emitted with every new byte? But it seems that the signal is only emitted at the begin of the package of the 3 bytes. Also my qDebug output doesn't react on changes from the PSoc. So when I change values at PSoc the output in qDebug doesn't change.

I already tried reading 3 Bytes (serial->read(3)) and then I first received some single bytes and after a few readings I get the 3 bytes I sended but this is not so reproducible.

    connect(serial, SIGNAL(readyRead()), this, SLOT(readData()));

    serial->setPortName(gui->ui->comboBox->currentData().toString());
    serial->setBaudRate(QSerialPort::Baud115200);
    serial->setDataBits(QSerialPort::Data8);
    serial->setParity(QSerialPort::NoParity);
    serial->setStopBits(QSerialPort::OneStop);
    serial->setFlowControl(QSerialPort::NoFlowControl);

    void uart::readData()
    {
        QByteArray data = serial->read(1); 
        qDebug() << data;
    }

I expect an output like "0x01" "0x02" "0x03" 2.5 times a second, but I get only "0x01"

Upvotes: 0

Views: 708

Answers (2)

cqRinO
cqRinO

Reputation: 23

I just found the solution! You have to set the read-buffer size to the right value. So for reading a package of three bytes I must set:

serial->setReadBufferSize(3);

Upvotes: 0

parti82
parti82

Reputation: 161

You are only reading a fixed size with read.

Could it be that you get readyRead signals with varying bytes available but you only read fixed size of them

In your readyRead slot try to read all available bytes.

qint64 available = serial->bytesAvailable();
if (available > 0)
{
    QByteArray data = serial->read(available);
    qDebug() << data;
}

You can also use readAll() function.

Upvotes: 2

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