Qt NFC 5.11 on Linux (neard)- Mifare 1k tag "uid" returned is empty

[fbelloni]

Hi,
I'm working with Qt Nfc 5.11 on my Linux board based on ARM processor (neard v0.16 is installed).

I'd like to read the UID of a Classic Mifare 1k Tag usign the following code:

Nfc::Nfc(QObject *parent) :
    QObject(parent)
{
    QLoggingCategory::setFilterRules("*.debug=true\n"
                                     "driver.usb.debug=true");

    manager = new QNearFieldManager(this);

    if (!manager->isAvailable()) {
        qDebug() << "NFC not available";
        return;
    }

    manager->setTargetAccessModes(QNearFieldManager::NdefReadTargetAccess);

    connect(manager, SIGNAL(targetLost(QNearFieldTarget*)), this, SLOT(targetLost(QNearFieldTarget*)));
    connect(manager, SIGNAL(targetDetected(QNearFieldTarget*)), this, SLOT(targetDetected(QNearFieldTarget*)));

    manager->startTargetDetection();
}

void Nfc::targetLost(QNearFieldTarget *target)
{
    qDebug() << "lost!!!";
}

void Nfc::targetDetected(QNearFieldTarget *target)
{
    qDebug() << "detect!!!";
    qDebug() << "UID:" + target->uid();
}

All seem to be ok: neard (v0.16) is running correctly, the driver of my NFC reader (PN532) with "i2c" interface is correctly installed and Qt doesn't report any issue. When I tap my tag on the NFC reader the tag is correctly detected.
My issue is that the "uid" returned by the Qt uid() method is empty. I debugged the driver and I'm sure that the uid is red correctly via i2c. I report below the output debug of this operation:

qt.nfc.neard: org.neard.Adapter found for path "/org/neard/nfc0"
qt.nfc.neard: starting target detection
qt.nfc.neard: adapter is already powered
qt.nfc.neard: successfully started polling
Echoserver listening on port 8080
Scan card screen
qt.opengl.diskcache: OpenGL ES v2 context
qt.opengl.diskcache: Shader cache supported = 0
qt.nfc.neard: tag found at path "/org/neard/nfc0/tag8"
qt.nfc.neard: tag type "Type 2"
detect!!!
"UID:"

qt.nfc.neard: tag removed "/org/neard/nfc0/tag8"
lost!!!

I noticed that after the tag detection, the tag is released by the driver automatically in few milliseconds (500ms) even if the tag is still on the NFC reader. I didn't understand why the driver releases the target but the time to read the uid should be enough.

• Do you have some advices to solve this issue?
• Could be a synchronization issue between the driver, neard and Qt?

Thank you for your help guys,
Fabrizio