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TMS570LC4357: How to disable CAN auto-answer on RTR message / request

v01d
Expert 2025 points
Part Number: TMS570LC4357
Other Parts Discussed in Thread: HALCOGEN

I've configured this message box for RTR, and it gets invoked when RTR request arrives. See pic below:

But, I have unwanted behavior , fact that the CAN controller seems automatically fires replies with whatever it had last loaded into this message box. 

So, for example, if I hold the CPU halted with debugger, and send RTR frame from PC host, I get reply from the devboard, even though the code is not running, so the CAN controller seems handling this request automatically.
Which I do not want at all, I need to reply to this request from the code.

And because I also have my own send response, now I get effectively two responses from the card: one which it always fires automatically, followed by my the reply as from code.  

My CAN trace would look like this:  

I read for other TI chip (here : https://www.ti.com/lit/ug/sprueu0/sprueu0.pdf?ts=1598526170937&ref_url=https%253A%252F%252Fwww.google.com%252F)  allows to disable this "Auto-Answer" mailbox/object feature, but I do not see how / where to do this with TMS570.

Is it possible to remove this automatic handling?  To pre-load values in advance into that box is not a good thing for me.

  • 0
    TI__Guru**** 197036 points

    If the RmtEn bit is set, a matching received Remote Frame will cause the TxRqst bit to be set; the Remote Frame will autonomously be answered by a Data Frame. This is the feature.

  • 0 in reply to QJ Wang
    Expert 2025 points

    QJ Wang,

    Yes, I have read that in the manual. So what that means, it is not possible to turn off "autonomously" answering?

    How does one need to set it up then :  If I have set it to RX direction && enable RTR, then I do not get the host's RTR message at all - I do not get the frame in. (without RTR I receive the frames).

    And if I'm forced to use that "autonomous" feature, how to pre-fill that buffer for auto-answer? I'm sketchy / if at all know how/where to do this...

    UPDATE: I see you can fill message object data (HalCoGen -> canFillMessageObjectData);   but still un-sure the proper way to pre-fill this specific box the very first time then, before first Tx request which comes already after the frame was sent out by the controller. 

  • 0 in reply to QJ Wang
    Expert 2025 points

    Also, QJ Wang,

    With this "autonomously" answering,  is it possible to map more than one CAN id then to same message box, how? 
    If I have say 10 ids mapped to same box,  which value will it send automatically back on RTR request?  ... I see only single hardware buffer , and TxRqst seems set after the frame was already sent out, so ..

    Is it possible to have more than 1 id per message box with RTR feature?

  • 0 in reply to v01d
    TI__Guru**** 197036 points

    No, each message object has only one unique message ID at a time. You can update the ID if you want. 

    You can get message with different message IDs by changing MASK to ignore some bits. 

    Writing 0 to a bit of MASK[28:0], the corresponding bit in the message identifier is not used for acceptance filtering (don't care).