CAN Communication in QT

Question

I have a specific problem with the CAN communication in QT. It is not a problem to send/write CAN messages, but the readFrame() function in QT doesn't load my received frames. If you are implementing a CAN communication in C++ you can use the read() and write() functions. But in QT it is not supported. In general the read function interrupts the programm until a message is received, how can I do the same in QT?

QCanBusFrame frame = device->readFrame();

Thanks for your help, I really appreciate it!

Did you connect framesReceived signal to your slot? – Farshid616 Sep 15 '21 at 10:44 — Farshid616, Sep 15 '21 at 10:44

score 0 · Accepted Answer · answered Sep 14 '21 at 13:49

0

From the QT docs:

Returns the next QCanBusFrame from the queue; otherwise returns an empty QCanBusFrame. The returned frame is removed from the queue.

The queue operates according to the FIFO principle.

https://doc.qt.io/qt-5.12/qcanbusdevice.html#readFrame

Try first calling

bool QCanBusDevice::waitForFramesReceived(int msecs)

https://doc.qt.io/qt-5.12/qcanbusdevice.html#waitForFramesReceived

and then read frames

answered Sep 14 '21 at 13:49

Shabbir Hussain

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Thanks for your reply. How can I call the "bool QCanBusDevice::waitForFramesReceived(int msecs)" in QT. In the header file or in mainwindow.cpp. – Sinan Kiris Sep 14 '21 at 14:27
`QCanBusFrame frame; if (device->waitForFramesReceived(1000)) { frame = device->readFrame();}` – Shabbir Hussain Sep 14 '21 at 18:42
Most likely, you're reading frames before the buffer has any. Adding a waitforFramesReceived will block execution for a period and then you may call readFrame? – Shabbir Hussain Sep 14 '21 at 18:44
What is your setup? What is sending and receiving, are you able to confirm that your physical setup is functional? – Shabbir Hussain Sep 15 '21 at 13:17
Yeah, everthing is working so far. I am monitoring the CAN messages over candump can0. There I receive every message. – Sinan Kiris Sep 20 '21 at 06:38
Thank you, it works! Instead of 1000 ms as value you can typ -1 (waitForFramesReceived(-1).Finally, the whole programm will wait for a CAN message. – Sinan Kiris Sep 23 '21 at 15:20
If I understand correctly, your solution was to do this: ` if (device->waitForFramesReceived(-1))` which waits until a frame is received? – Shabbir Hussain Sep 24 '21 at 18:25
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Yes, correct! :) – Sinan Kiris Sep 26 '21 at 21:42

CAN Communication in QT

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