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CAN bus CRC - Probability of Undetected Failure

William Glover

I wonder if anyone could help me please.

I am writing an assessment of the safety implications of functions that are reliant on a CAN bus.  

More specifically, I am interested in the Probability of Undetected Failure of the CAN bus CRC-15 Cyclic Redundancy Check.  I have found some figures and graphs for some specific CRCs, for some Bit Error Ratios, but not for the specific CRC of interest.  I know there are ways of calculating these figures given the CRC polynomial, packet length, and BER, but in the papers I have seen, the maths looks a bit beyond me.  Also, as it is a commonly used CRC I am interested in, I was hoping to find a source of pre-calculated values, ideally for a range of BERs.

Any assistance or guidance would be appreciated. 

Thanks

Bill

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    Hmm the question seems to be about the CRC specifically, just applied to the slightly thorny problem of variable length CAN packets. There is a lot written about the chances of errors being missed under a CPC, but there are real situations, such as bursts of interference or periodically repeating  interference that complicate the answer relative to the white noise normally considered in the text books.

    Certainly it  is  possible to have far more un-spotted errors than the simple case suggests, if the errors are non-random. My maths is not really good enough to go far beyond this.

    Mike

  • 0 in reply to mapj1

    The main point for me is the relevance to safety. If it is a safety-related calculation then the piece of kit is being used in a safety-related application. That will necessarily have been assessed - or is being assessed - against some standard (IEC 61508; IEC 61511, ISO 26262, etc). The manufacturer of the kit will have the kind of information that allows users to use their kit in safety-related applications according to that standard. As a matter of due diligence, you have first to ask them for their HRA, or data relevant for yours. That is why I suggested it.

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  • 0 in reply to mapj1

    The main point for me is the relevance to safety. If it is a safety-related calculation then the piece of kit is being used in a safety-related application. That will necessarily have been assessed - or is being assessed - against some standard (IEC 61508; IEC 61511, ISO 26262, etc). The manufacturer of the kit will have the kind of information that allows users to use their kit in safety-related applications according to that standard. As a matter of due diligence, you have first to ask them for their HRA, or data relevant for yours. That is why I suggested it.

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