docs: Note canbus_query.py limitations in CANBUS_Troubleshooting.md

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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Kevin O'Connor 2025-04-29 13:51:40 -04:00
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@ -118,6 +118,23 @@ necessary to increase the `txqueuelen` above the recommended value
of 128. However, as above, care should be taken when selecting a new of 128. However, as above, care should be taken when selecting a new
value to avoid excessive round-trip-time latency. value to avoid excessive round-trip-time latency.
## Use `canbus_query.py` only to identify nodes never previously seen
It is only valid to use the
[`canbus_query.py` tool](CANBUS.md#finding-the-canbus_uuid-for-new-micro-controllers)
to identify micro-controllers that have never been previously
identified. Once all nodes on a bus are identified, record the
resulting uuids in the printer.cfg, and avoid running the tool
unnecessarily.
The tool is implemented using a low-level mechanism that can cause
nodes to internally observe bus errors. These internal errors may
result in communication interruptions and may result is some nodes
disconnecting from the bus.
It is not valid to use the tool to "ping" if a node is connected. Do
not run the tool during an active print.
## Obtaining candump logs ## Obtaining candump logs
The CAN bus messages sent to and from the micro-controller are handled The CAN bus messages sent to and from the micro-controller are handled