Run SerialServer only with custom PDU #2719
Replies: 1 comment 3 replies
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v3.10 is a non functional release, please upgrade to v3.11. When you register a request/response the function code + sub function code in the class are appended to the lookup tables. . You can create new function codes or overwrite existing ones, and if overwriting existing ones your class should be called instead of the default one. Since the registration updates the lookup tables, that is the supported way. You do not share your customRequest so I cannot see if it is a new function code, or you inherit from an existing one. I assume you are aware that "large amounts of data" are limited be fit within the 255byte frame size ? If you try send send a frame bigger than 255bytes, then you will encounter problems. What is really disturbing is that it only happens under load...that seems like a concurrency problem, but since the lookup table is static I cannot see what could cause a wrong lookup. So in total please attach at least the top part of your customRequest, together with a debug log (you can use the Pymodbus call to activate debugging), allowing me to see what is happening and analyze what the problem could be. |
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Upgrade done, no change. This is what my custom request looks like: class CustomModbusRequest(pdu.ModbusPDU):
"""Use this class to register our custom Modbus function code (0x42) with pymodbus."""
function_code = 0x42
rtu_frame_size = 8 # todo: which?
def __init__(self, dev_id: int = 1, transaction: int = 0):
"""Initialize as done in the custom message example in pymodbus.
We need the dev_id argument as it is used for the modbus address, which we need.
Not sure about the transaction argument, but just following
https://github.com/pymodbus-dev/pymodbus/blob/fbf2cef0328f096822707ed068d7362e685f1be8/examples/custom_msg.py#L72
""" # allow long URL
super().__init__(dev_id=dev_id, transaction_id=transaction)
self._raw_packet: bytes
self._response_packet: CustomPacket
def encode(self) -> bytes:
"""Fake abstract method placeholder - although mypy is somehow not complaining."""
raise NotImplementedError
def decode(self, data: bytes) -> None:
"""`dev_id` is not properly set here yet, so only save the raw data for now."""
_log.debug(f"Received modbus data: {data=}.")
self._raw_packet = data
async def update_datastore(
self, context: datastore.ModbusDeviceContext
) -> pdu.ModbusPDU:
"""Use this command to send a modbus response to the client.
Only here the `dev_id` is properly set to the correct address so we can properly store
state per address.
"""
_ = context # unused but injected by pymodbus
_log.debug(f"Handling {self._raw_packet=} for {self.dev_id=}...")
self._response_packet = handle_raw_packet(
self._raw_packet, modbus_address=self.dev_id
)
_log.debug(f"Going to reply with {self._response_packet=}")
return CustomModbusResponse(
dev_id=self.dev_id,
transaction=self.transaction_id,
response_packet=self._response_packet,
)Yes I'm aware of the size constraints and am using ~100bytes now, so well below the limits. Some log excerpt where it happened again: In general with these higher data transmission packets I get a looot of those frame check failed logs.
Yes I saw that, but I need the modbus server to only recognize my custom packages and nothing else. Thank you for your help. |
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I need to see the last frames being sent/received before the frame check fails, without that I cannot analyze. The failed frame check typically indicates a couple of problems:
Function code 0x42 is not defined in the default set, so it makes it even stranger, why it stops detecting it, However the frame check failed indicates that the server receives false data. I know the upgrade to 3.11 did nothing to solve your problems, but if you decide to try other request. |
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Are you sure your client handles the high baudrate ? also at this speed your rs485 cabling needs to be in a top state...did you remember the terminating resistor. |
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Hello,
first of all thanks for the great library! 😺
I use version 3.10 and start a server like this:
In
CustomModbusRequestI register my custom function code and use it to handle a separate protocol which is just using modbus as a transport protocol.For single requests and not a lot of data being sent everything works well. Only if a lot of requests with a large amount of data are being sent problems occur.
Then the modbus server sometimes detects one of the default function codes and acts upon it and thus bricking the communication (see log message below).
My current hack is to disable the lookup of the "default" function codes here
pymodbus/pymodbus/pdu/decoders.py
Lines 75 to 82 in b9731ec
Is there any supported way to do this? If not could we add one?
Thanks for your time!
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