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EKS-LM4F232 CAN0 does not seem to be handling the ack bit

John Osen
Genius 3585 points

I have an EKS-LM4F232 in a CAN network that has a Kvaser USB-CAN interface and a CAN display.  The display sends out about 4 messages per second.  When all are on the bus, the USB interface sees all the messages generated by the display, as does the EKS.  When I send a message out on the CAN bus from the USB interface, the EKS sees it.  Now when I power down the display, both the USB interface and the EKS stop seeing messages.  When I now send a message out of the USB-CAN interface, I see a chain of bus errors and the USB goes into error-passive mode.  It is as if the EKS is not there.  I suspect that the EKS is not setting the ACK bit, so the USB interface thinks nobody is out there an just starts retransmitting.

Do I need to do something special to the EKS CAN to avoid this?

  • 0
    Guru 47900 points

    John Osen said:
    When I send a message out on the CAN bus from the USB interface

    This is a bit too vague for several of us to properly grasp.  Are you in fact "just" transmitting via EKS's USB port - and externally converting to CAN?  The "mix" of USB and CAN (as described) is troubling to our group.  Personally I think you are not USB>CAN converting - added clarification requested.

    Can you provide part no./link to Kvaser - so that the device you describe may be reviewed?  Many - this forum - seek low cost means of commissioning/verifying their CAN Aps - perhaps the device you've described may prove suitable...

     

  • 0 in reply to cb1
    Genius 3585 points

    Thanks for your rapid response.  Your question clearly exposes how vague my description was.  I am not using any USB capability on the EKS.  The USB interface to which I refer is plugged into my PC.  A simple application runs on the PC that uses the USB interface to snoop the CAN bus and electively put messages on the can bus.  The USB interface is completely independent of the EKS.  The Kvaser link would be found googling 'Kvaser Leaf Light' or www.kvaser.com/prod/hardware/leaf_light.htm.  I doubt you need it though.  It is just a third-party CAN device I can drive from my PC.

  • 0
    Guru 47900 points

    Thank you - response delayed as I was poked/prodded by scheduled med. test (rather than boss) today.

    You link did help - still uncertain re:

    John Osen said:
    when I power down the display
      Is it not possible that your CAN display - when powered down - someway/how causes a CAN bus issue?  Is that CAN display certified to "sit on the bus" (causing no harm) when unpowered?  Seems that smaller, simpler CAN bus population (i.e. remove the troublesome CAN display) would rule out 3rd party issues - and better enable you to focus on any potential issue with your 4F232. 

    To this reporter appears that your CAN display is as much (and likely more) a source of problem than your EKS.  Perhaps some part no./description of the CAN display would further assist...