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I have a strange finding about the heartbeat-protocol in CANopen. Maybe somebody else has seen something like this and maybe it is supposed to work like this... Anyway, here's what it's about:

In CANopen there are two timeout-based life-guarding mechanisms: the first is node guarding, which I will not mention further, since it's considered old news.

The other one is called heartbeat. It is pretty simple: Any participant on the network sends a regular message stating its node ID and its state. The frequency is defined by object 0x1017sub0 and is called heartbeat-producer-time. If it is set to zero, no heartbeat is being sent.

Any other participant can then define a number of nodes it wants to find on the network plus the maximum time there may be between two consecutive heartbeat-messages. This information is stored in object 0x1016sub1..n as 32-bit entries for as many nodes as this particular node wants to listen to.

The entries consist of the node ID (bits 22 to 16) and the mentioned maximum time that may elaps between heartbeats, called the heartbeat-consumer-time (in bits 15..0). Again if the entry is zero, it is being ignored.

As you may have gathered, there is no distinction between network-master (node ID 1) and slaves (node IDs 2 to 127).

So far the theory, now for my problem:

I configure one of the slave-nodes in my network as a heartbeat-consumer for the master, so there's an entry in object 0x1016sub1 that looks like this: 0x000107D0. Meaning that a heartbeat-message from the master is expected after at least two seconds.

I have observed that this works in two examples. If I send a master-heartbeat for a time and then stop, the node either returns to pre-operational mode or sends an appropriate emergency-message.

If I don't send any master-heartbeat-messages, I would expect that after I start the node (send it into operational mode) it takes at most two seconds for the node to either return to pre-operational mode or send an appropriate emergency-message or perhaps even both. But in the two examples I tried, nothing happened. If I never send any heartbeat, the node never expects one and just keeps on running.

The two examples are very different from each other. I am not sure whether they use the same CANopen-stack library perhaps.

Is there an explanation?

Peter Mortensen
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Henning
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1 Answers1

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If you read CANopen User Manual, section 1.3.1.6, page 39, you will notice that the heartbeat consumer is first activated upon receiving a heartbeat from the producer. I would assume then that, since in your example the first heartbeat is never sent, the consumer is not activated.

Peter Mortensen
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erik kelley
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  • @Peter, would you like to relink the `CANopen User Manual`? The previous link is down. – asys Aug 23 '22 at 10:13