Ahhh.. that explains it then. Thank you.
You just can't see the side when it's mounted on a heavily populated DIN rail! I was unlucky enough to get two with the printing error.

Ok I'm having trouble seeing these CAN messages on our CANKing monitor.

When the two RevPi's are talking to each other, they can see the messages but the CANKing can't.
When I put the CANKing on our test rig, it can see CAN messages, but the RevPis can't.
A quick look with an oscilloscope showed ...

Thank you.

I can see that uses the equivalent of system() calls but from within python. I know that the command line works and am trying to get the standard C libraries to work.

I have finally succeed! https://gist.github.com/Hansen-KK
Cross compiling in Visual Studio logged in to RevPis as root.

That explains it.. command line I'm using sudo, cross platform debugging using standard Pi login.

With root login for debugging, those commands now run without error. Still doesn't work yet, but getting closer.

All examples I can find online use libsocketcan to interact with the can0 device from within C.

By using the following commands I can get the can0 connection to be seen as "UP" and then the example C code works:
~$ sudo ip link set can0 type can bitrate 250000
~$ sudo ip link set up can0

However ...

Of course I have modified it to connect to the "can0" you mentioned above, which is why I asked. (line 29 in receive and line 28 in transmit)

I have now managed to send and receive over CAN by using a combination of command line to set the CAN to UP and the C code above. Having proven the ...

Thank you. I have removed that and it works now. My mistake, I'm flipping between two Industrial Pi platforms for a technology validation project and must have enabled that on the incorrect platform.

We're on a roll now!

Four files are attached.
The initial files are what I get immediately after a power cycle. the DIO is showing a red LED, the RevPi a green one.
Then I ran piTest -x, the files suffixed with _good are with both RevPis and DIOs showing green LEDs

I am using these as example code:

https://github.com/craigpeacock/CAN-Examples

I am running my two RevPi's, one with the transmit code, one with the receive code, but both report network down.
When I add in can_get_state() from libsocketcan I get a state of CAN_STATE_STOPPED

CAN Sockets ...

Sorry missed mentioning that. They're both without any of those lines and always fail to start on reboot or power cycle. At best I can start them with piTest -x, at worse I have to completely reload everything and power cycle.
(yes, I've updated and upgraded them today)