I have a CAN bus application that has been working well in Qt 5 (latest Qt 5.15.2). I'm having issues with Qt 6.2.0 Alpha and Beta1.

With an external CAN node connected and periodically transmitting, a QCanBusDevice on the PC Qt App is initialized and connected. CAN frames can be read once using QCanBusDevice::readAllFrames(), but subsequently, no further CAN frames are available.

Minimal example code below (readAllFrames() is not used in this example):

MainWindow::MainWindow(QWidget *parent) 
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{ 
    ui->setupUi(this);  

    QString errorString; 
    // device is a QCanBusDevice*
    device = QCanBus::instance()->createDevice(
        QStringLiteral("peakcan"),
        QStringLiteral("usb0"), 
        &errorString
    );  
    device->setConfigurationParameter(QCanBusDevice::BitRateKey, 500000);      
    device->connectDevice();

    // timer is a QTimer*
    timer = new QTimer(); 
    timer->setInterval(100);
    connect(timer, SIGNAL(timeout()), this, SLOT(timerSlot()));
  
    timer->start();
} 

void MainWindow::timerSlot()
{ 
    qDebug() << device->busStatus() << device->framesAvailable();
}

• In Qt 5.15.2, the framesAvailable() value will keep increasing
• In Qt 6.2.0, the framesAvailable() is stuck at a small number (approx 100+)
  • I am able to readAllFrames() on those available frames, then framesAvailable() will be stuck at 0, and doing more readAllFrames() will produce empty lists.
  • Calling resetController() will allow a fresh set of frames to be populated, but this is not a valid workaround since many frame are lost.
• In both cases, the busStatus() is always CanBusStatus::Good

Using PCAN-USB from Peak Systems.