XNET CAN frame queue overrun kills Read VI

[pgraebel]

Hello, I am trying to read CAN frames via XNET. My problem seems to be connected to the queue of my Input session: If the queue gets bombed with random CAN messages from somewhere, the session property "Number of Values Pending" increases rapidly. That's ok, because my program calls XNET Flush before it starts using the bus itself. Otherwise my program would read the old queue content first and the expected reply frames later. This behaviour is ok and expected.

But after I bombed the bus a little bit more so that the queue gets filled to maximal queue size (seems to be predefined as 1000), the Input session read operation will always timeout (tested with 1 second and more) and return an empty frame array. In this case the error wire is s to -1074384886 (timeout). The session always reports tranceiver state "Normal". Even the XNET Flush operation does not help, although it seems to empty the queue properly.

summary: hitting the queue size limit with incoming CAN frames results in dead read operations.

[O_Proulx]

Hello pgraebel,

In the screenshot you posted, NI-XNET will wait 0.1seconds for 1 frame to be present in the queue.  If there is less than 1 fram available, the VI will timeout.  That being said, I would guess that the timeout happens if you ask for many frames (close to the buffer limit), but the timeout is too small.  If you are trying to read 1000 frames, you may need to wait longer than 1 second for the frames to go on the bus.  That really depends on your bus timing/frame timing/etc.

I made a small example to show you a little more how the buffers can be used in XNET.  You can set the buffer size and look at the unused spaces in both the read and write queue.  Let me know if it helps.