QT6 QCanBus not decoding Frames correctly.

Guy Radford

I am using a Mac and have followed the https://doc.qt.io/qt-6/macos.html & https://doc.qt.io/qt-6/qtserialbus-peakcan-overview.html documentation.

I am using QT6.4.1 for MacOS.

When QT receives a Can Frame it is decoding the data incorrectly.

On my Mac, the CAN data is being correctly displayed when receiving the CAN Data via Python or the MacCAN Monitor tool. The IDs are correct, the payload length is correct and the data is correct. (The actual payload will vary slightly over time and therefore the actual data within the payload varies slightly, but the shape of the data is consistent.)

Example Python Output:

ID=00A LEN=8 DATA=[00 00 47 0A 6E 02 00 00]
ID=00B LEN=8 DATA=[E9 2F 4D 42 0E 67 AC BE]
ID=00A LEN=8 DATA=[00 00 47 0A 6D 02 00 00]
ID=00B LEN=8 DATA=[E9 2F 4D 42 28 66 AC BE]
ID=002 LEN=2 DATA=[06 3A 00 00 00 00 00 00]
ID=00A LEN=8 DATA=[00 00 47 0A 6A 02 00 00]
ID=00B LEN=8 DATA=[EA 2F 4D 42 CA 65 AC BE]
ID=00A LEN=8 DATA=[00 00 47 0A 6E 02 00 00]

With QT I am getting the following with qDebug() << canFrame.toString() << " Payload: " << canFrame.payload(); (Full code below)

"0000000A   [6]  E3 00 00 00 00 00"  Payload:  "\xE3\x00\x00\x00\x00\x00"
"     00B  [66]  Remote Request"  Payload:  "\x06^\xAC\xBE\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\xC4\x00\x00`\x00\x00\x10/!\x00\x00`\x00\x00)\x00@\xFF""e>'\xB8\n\x00\x00 E\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"0000000A   [6]  E3 00 00 00 00 00"  Payload:  "\xE3\x00\x00\x00\x00\x00"
"     00B  [66]  Remote Request"  Payload:  "\x06^\xAC\xBE\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\xC4\x00\x00`\x00\x00\x10/!\x00\x00`\x00\x00)\x00@\xFF""e>'\xB8\n\x00\x00 E\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"     002   [0]"  Payload:  ""
"0000000A   [6]  E3 00 00 00 00 00"  Payload:  "\xE3\x00\x00\x00\x00\x00"
"     00B  [66]  Remote Request"  Payload:  "\x07^\xAC\xBE\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\xC4\x00\x00`\x00\x00\x10/!\x00\x00`\x00\x00)\x00@\xFF""e>'\xB8\n\x00\x00 E\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"0000000A   [6]  E3 00 00 00 00 00"  Payload:  "\xE3\x00\x00\x00\x00\x00"
"     00B  [66]  Remote Request"  Payload:  "\x07^\xAC\xBE\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\xC4\x00\x00`\x00\x00\x10/!\x00\x00`\x00\x00)\x00@\xFF""e>'\xB8\n\x00\x00 E\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"0000000A   [6]  E3 00 00 00 00 00"  Payload:  "\xE3\x00\x00\x00\x00\x00"
"     00B  [66]  Remote Request"  Payload:  "\t^\xAC\xBE\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\xC4\x00\x00`\x00\x00\x10/!\x00\x00`\x00\x00)\x00@\xFF""e>'\xB8\n\x00\x00 E\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"0000000A   [6]  E4 00 00 00 00 00"  Payload:  "\xE4\x00\x00\x00\x00\x00"

I am expecting the following:
Frame ID 0x02 to have a length of 2, not 0 bytes.
Frame ID 0x0A to have a length of 8, not 6 bytes.
Frame ID 0x0B to have a length of 8, not 66 bytes.

None of the Frame IDs are extended, yet QCanBus is reporting 0x0A as extended.

Here is the code used to generate the above QT output:

CanBusTest.pro

QT += quick serialbus

SOURCES += \
        main.cpp

resources.files = main.qml 
resources.prefix = /$${TARGET}
RESOURCES += resources

# Additional import path used to resolve QML modules in Qt Creator's code model
QML_IMPORT_PATH =

# Additional import path used to resolve QML modules just for Qt Quick Designer
QML_DESIGNER_IMPORT_PATH =

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

QMAKE_APPLE_DEVICE_ARCHS = x86_64 arm64

main.cpp

#include <QCanBus>
#include <QGuiApplication>
#include <QQmlApplicationEngine>

class FrameReceiver : public QObject {
  public:
    FrameReceiver(QObject *parent = nullptr, QCanBusDevice *device = nullptr) {
        this->device = device;
        connect(device, &QCanBusDevice::framesReceived, this, &FrameReceiver::onNewFrame);
    }
  public slots:
    void onNewFrame(void) {
        while (this->device->framesAvailable()) {
            QCanBusFrame canFrame = this->device->readFrame();
            qDebug() << canFrame.toString() << " Payload: " << canFrame.payload();

        }
    }

  private:
    QCanBusDevice *device;
};

int main(int argc, char *argv[]) {
    QGuiApplication app(argc, argv);

    QString errorString;
    QCanBusDevice *device =
        QCanBus::instance()->createDevice(QStringLiteral("peakcan"), QStringLiteral("usb0"), &errorString);

    device->setConfigurationParameter(QCanBusDevice::BitRateKey, QVariant::fromValue(250000));
    qDebug() << "Can Device: " << device;
    device->connectDevice();

Thank you for your help.

Guy Radford

@Guy-Radford

This appears to be a bug as the CAN Frames are decoded correctly on a windows machine, I have raised a Bug report with QT:

https://bugreports.qt.io/browse/QTBUG-113538