Re: Single shot mode with arbitration support

Hello John, Daniel,

I agree with Daniel. The errorframe is essential. Presume a transmitting node detects a biterror during sending. If it just stops, how would the receiving nodes, which have not detected the error, know that an error occured. OK if the transmission just stops, they will see only recessive bits and in that case they would also like to send an errorframe. This should also be prohibited, which really means you don't have a CANbus anymore. I would call this CAN version 0.0.

The SJA1000 does a single-shot transmission. If it does not succeed, it sends its errorframe and waits until the software says: "Try again". This should fulfill the MILCAN specification.

In the design of the network you should calculate a maximum frame length not only the CANframe, including maximum number of stuffbits, but also the 20 bits of one extra errorframe (12 times 0 + 8 times 1). I must correct this during my writing, because if an error occurs the errorframe will come before the EOF/IFS starts, so we can subtract 10 bits, which leaves 10 bits extra in the calculation. This seems no problem to me.

Kees

  ----- Original Message ----- 
  From: Daniel Leu 
  To: [email protected] 
  Sent: Friday, January 18, 2013 7:50 AM
  Subject: Re: [CANLIST] Single shot mode with arbitration support


  Hi John,


  The revision history of MilCAN A Complete Rev3 has as first entry



    1 March 2006 Initial publication.
    Merger of the following documents: MilCAN A Physical Layer Specification (IHSDB-APP-GEN-D-030 Rev 3)
    MilCAN A Data Link Layer Specification (IHSDB-APP-GEN-D-031 Rev 4)  *********
    MilCAN A Application Layer Specification (IHSDB-APP-GEN-D-032 Rev 2)



  Looks like the specification you referenced is now included in MilCAN A, rev3.


  Paragraph 3.10 becomes 3.2.10


    • 3.2.10  Link Layer Re-transmission on Error - Compulsory

    The LLC sub-layer of the ISO11898 CAN standard includes amongst its functions the re- transmission of frames that have been disrupted by errors during transmission. This process can result in an unpredictable number of re-transmissions of the same frame in the event of errors.

    Automatic re-transmission on error shall be prohibited where this would violate the requirements of prioritised queuing as stated in section 3.2.7.1. Corrective procedures appropriate for the system application may then be executed by the node/device application software.


  To me this defines the requirement for disabling automatic re-transmission. But this doesn't say anything about not having an error flag.


  I can't really imagine that a CAN HLP disallows an essential CAN feature such as the error flag.




  Regards,
  Daniel








  On Jan 17, 2013, at 6:46 PM, John Dammyer <[email protected]> wrote:


    Hi Daniel,

    See below.  Unless it's changed.

    John

    From:
    MilCAN A
    Data Link Layer Specification
    IHSDB-APP-GEN-D-031
    Revision 4

    3.10 Link Layer Re-transmission on Error - Compulsory
    The LLC sub-layer of the ISO11898 CAN standard includes amongst its
    functions the retransmission
    of frames that have been disrupted by errors during transmission. This
    process can result in an unpredictable number of re-transmissions of the
    same frame in
    the event of errors.
    This function shall be disabled by selecting CAN controllers that provide
    the capability to
    disable re-transmissions. Corrective procedures appropriate for the system
    application
    may then be executed by the node/device application software



    -----Original Message-----
    From: [email protected]
    [mailto:[email protected]] On Behalf Of Daniel Leu
    Sent: January-17-13 6:09 PM
    To: [email protected]
    Subject: Re: [CANLIST] Single shot mode with arbitration support

    Hi John,


      The problem is MilCAN doesn't allow error flags since a bad message 
      retrying could easily overlap into the next SYNC message window.  The 
      architecture of a MilCAN system is such that the designer plans what 
      messages occur during each SYNC slot.  A node may broadcast only when the

    SYNC COUNTER was 24.

      Another only when 32 and so on.   


    Just wondering where in the MilCAN spec it says that error flags are not
    allowed. Thanks!


    Regards,
    Daniel




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