I got a subflow to handle modbus retries. Because modbus requests are highly unstable and fails multiple times each hour. Quick and dirty solution is to run the request again 1 or 2 more times until it succeeds.
For this to work, I need precise handling of errors/exceptions. It is also good to have a 2nd error ouput to support the case when the request that failed was part of a group to be joined later in parent flow.
Modbus flex getter has many different options:
- Empty msg on Modbus fail
- Keep Msg Properties
- Show Activities
- Show Errors
- Show Warnings
Then the context node also has a set of options:
- Log states changes
- Log failures
- Show Errors
- Show Warnings
- Show Logs
I don't understand the details of all these options, for example what is the difference between Show Errors and Log failures? Furthermore, I don't understand what happens if I set a specific setting in the node and/or the context node.
I monitor 12 values to export every minute. When these settings are disabled, I get no exception in parent's catch (set to catch all). When I enable them, I also don't get any exceptions when data is missing. If I set Empty msg on Modbus fail, I get an output message which I use to throw an exception (to be logged and possibly retried). But that empty message doesn't have the Msg Properties, so all meta-data about the context of that particular msg is lost. And so the retry fails.
How is it possible to make a retry mechanic for modbus? How to precisely capture every msg which request doesn't return successfully with a value?
This was very easy to do with for example http node. I need some help to understand how it's possible to manage with modbus. Thanks in advance for any insight.
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}
],
"x": 550,
"y": 340,
"wires": [
[]
]
},
{
"id": "4a75d82c6ec39ab7",
"type": "catch",
"z": "692b7a4cf60bbc70",
"name": "catch modbus",
"scope": [
"54509e994c668256"
],
"uncaught": false,
"x": 270,
"y": 420,
"wires": [
[
"23fd3630c7140e81"
]
]
},
{
"id": "23fd3630c7140e81",
"type": "function",
"z": "692b7a4cf60bbc70",
"name": "invalid json",
"func": "msg.errorMsg = `Modbus threw an exception!`;\nif (msg.logError) {\n msg.logMessage = msg.errorMsg;\n}\n\nnode.error(msg.errorMsg);\nreturn msg;",
"outputs": 1,
"timeout": 0,
"noerr": 0,
"initialize": "",
"finalize": "",
"libs": [],
"x": 450,
"y": 420,
"wires": [
[
"64f8edf4788d0f18"
]
]
},
{
"id": "64f8edf4788d0f18",
"type": "subflow:a5184c5aab2f6cda",
"z": "692b7a4cf60bbc70",
"name": "",
"env": [
{
"name": "logCompleteMsgObj",
"type": "bool",
"value": "true"
}
],
"x": 630,
"y": 420,
"wires": [
[]
]
}
]
It sure ain't pretty:
.. but why do you have to do this "manual" retry for failed modbus reads ?
