I understand PGN and SPN, Copperhill was a great book. What I've been trying to get a better understanding is DD Identifiers and how they fit in? BTW, I was a electronics instructor for years, nice job. I relied a lot on student feedback to progress a class, you did it by yourself, impressive.
At the beginning of this episode you state this bus is pretty well loaded. How is it determined when the bus becomes overloaded? Are messages lost, or is transmit/receive just delayed?
I ran a CAN log taken around the same time as the scope recording through an engineering tool to determine the bus loading. Average load was about 50% with several peak loadings periods of 100% which appear to be captured in the scope recording. Visually on the scope, the amount of time where no controller is using the bus is very limited which is a rough indication of bus loading. Answering your question on lost messages, it somewhat depends on what the designers of the controller have done and how long the high loading occurs. Ideally, a controller which looses arbitration repeatedly because of high bus loading is able to eventually get any messages held in a queue in that controller onto the bus. At some point, the controller will likely flush the queue which result in those messages never getting to the bus. In practice, I have seen where some controller is blabbering junk messages result in communication timeout faults or machine performance issues. I plan to discuss CAN errors in future videos. Thanks for asking.
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I understand PGN and SPN, Copperhill was a great book. What I've been trying to get a better understanding is DD Identifiers and how they fit in? BTW, I was a electronics instructor for years, nice job. I relied a lot on student feedback to progress a class, you did it by yourself, impressive.
Thanks Don. I am not sure what you mean by DD identifier. Is this the address claim identity number?
At the beginning of this episode you state this bus is pretty well loaded. How is it determined when the bus becomes overloaded? Are messages lost, or is transmit/receive just delayed?
I ran a CAN log taken around the same time as the scope recording through an engineering tool to determine the bus loading. Average load was about 50% with several peak loadings periods of 100% which appear to be captured in the scope recording. Visually on the scope, the amount of time where no controller is using the bus is very limited which is a rough indication of bus loading. Answering your question on lost messages, it somewhat depends on what the designers of the controller have done and how long the high loading occurs. Ideally, a controller which looses arbitration repeatedly because of high bus loading is able to eventually get any messages held in a queue in that controller onto the bus. At some point, the controller will likely flush the queue which result in those messages never getting to the bus. In practice, I have seen where some controller is blabbering junk messages result in communication timeout faults or machine performance issues. I plan to discuss CAN errors in future videos. Thanks for asking.