QCanBusDevice: Error "Network is down"

[MHermann]

Hi all!

At the moment I am trying to use QCanBusDevice and QCanFrame for CAN communication.
I am able to set up the connection and to configure the device.
But if I try to send a message via

QCanBusDevice::writeFrame(const QCanBusFrame &frame) 

I get the error

QCanBusDevice::WriteError (2)

which means

"Network is down".

Has anyone an idea what causes this error and how to solve it?

Regards,
MHermann

[aha_1980]

Hi @MHermann, and welcome to the forum!

Which CAN plugin do you use? If you, for example, use SocketCAN, you will have to set up the CAN network before: http://doc.qt.io/qt-5/qtserialbus-socketcan-overview.html#socketcan-usage

[MHermann]

@aha_1980 :
Yes. I am using SocketCAN. Setting up the CAN network is done at system startup by a little script.
Otherwise

QCanBusDevice::connectDevice()

would fail.
Or does a successful connect not indicate, that the CAN network setup is correct?

[aha_1980]

@MHermann said in QCanBusDevice: Error "Network is down":

Or does a successful connect not indicate, that the CAN network setup is correct?

I can not tell you exactly at the moment, maybe it succeeds if the can device is present but not up.

You could try sending a test frame with cansend to see if you SocketCAN setup is correct.

Also please tell me: which Qt version are you using?

[MHermann]

@aha_1980 :

Thanks for your help.
I found the error. Now the CAN communication is working.

The code for setting up the CAN network was correct, but the script was not executed at startup. :|
I think I would not have checked the script again without your hint.

Btw. I am using Qt5.9.