Reading Gavazzi EM340 Modbus with Raspberry Pi 4B and pymodbus (Python 3.9.2)

[aritakku]

Hi. I hope this question finds you all well. I have Modbus/M-bus -enabled energymeter ( Gavazzi EM340, https://web.evishine.dk/wp-content/uploads/2019/11/EM340-ENG.pdf ) connected to Raspberry Pi 4B ( via RS422 / RS485 Serial HAT ( https://thepihut.com/products/rs422-rs485-serial-hat ). When booting the Rasp, it gives promising log entries:

fe201000.serial: ttyAMA0 at MMIO 0xfe201000 (irq = 34, base_baud = 0) is a PL011 rev2
fe215040.serial: ttyS0 at MMIO 0xfe215040 (irq = 35, base_baud = 62500000) is a 16550

However, I cannot read the energymeter via Rasp, using the pymodbus. Problem is that I cannot run the examples from ssh. (Rasp is headless)

Output from one example gives:

Traceback (most recent call last):
  File "/home/pi/pymodbus/new_virtual_env/test/./esim_modbus_payload.py", line 14, in <module>
    from examples.client_async import run_async_client, setup_async_client
ModuleNotFoundError: No module named 'examples'

Any help, or if anyone has a working example with reading /dev/ttyS0 it, would be highly appreciated.

[janiversen]

??? all examples are capable of being run in a normal shell, thus also with ssh. All my raspberry’s are headless and running ssh from another computer/table/phone works perfectly.

Seems you did not clone pymodbus…if you clone pymodbus you will have a directory called “examples”.

[aritakku]

Thanks for the quick reply. The git clone died with connection. So I downloaded the 3.1.1 tar.gz and it has the example dir.

(new_virtual_env) root@vadelma:/home/pi/pymodbus/new_virtual_env# ls -lah
total 128K
drwxr-xr-x 9 root root  4.0K Jan 24 14:54 .
drwxr-xr-x 4 root root  4.0K Jan 24 14:44 ..
drwxr-xr-x 3 root root  4.0K Jan 24 14:28 bin
-rw-r--r-- 1  501 staff  20K Jan 24 10:36 CHANGELOG.rst
drwxr-xr-x 2 root root  4.0K Jan 24 14:26 include
drwxr-xr-x 3 root root  4.0K Jan 24 14:26 lib
-rw-r--r-- 1  501 staff 1.4K Oct 24 13:34 LICENSE
-rw-r--r-- 1  501 staff   81 Oct 24 13:34 MANIFEST.in
-rw-r--r-- 1  501 staff  18K Jan 24 10:44 PKG-INFO
drwxr-xr-x 8  501 staff 4.0K Jan 24 14:18 pymodbus
drwxr-xr-x 2  501 staff 4.0K Jan 24 14:28 pymodbus.egg-info
-rw-r--r-- 1 root root    69 Jan 24 14:26 pyvenv.cfg
-rw-r--r-- 1  501 staff  17K Jan 24 10:36 README.rst
-rw-r--r-- 1  501 staff 2.0K Jan 14 23:21 requirements.txt
-rw-r--r-- 1  501 staff 7.4K Jan 24 10:44 setup.cfg
-rw-r--r-- 1  501 staff 1.1K Jan 14 23:21 setup.py
drwxr-xr-x 3 root root  4.0K Jan 24 14:26 share
drwxr-xr-x 2  501 staff 4.0K Jan 24 14:32 test

[aritakku]

Running the example modbus_payload results:

Traceback (most recent call last):
  File "/home/pi/pymodbus/new_virtual_env/./esim_modbus_payload.py", line 14, in <module>
    from examples.client_async import run_async_client, setup_async_client
ModuleNotFoundError: No module named 'examples'
(new_virtual_env) root@vadelma:/home/pi/pymodbus/new_virtual_env#

Script code begins:

#!/usr/bin/env python3
"""Pymodbus Client Payload Example.

This example shows how to build a client with a
complicated memory layout using builder-


Works out of the box together with payload_server.py
"""
import asyncio
import logging
from collections import OrderedDict

from examples.client_async import run_async_client, setup_async_client
from examples.helper import get_commandline
from pymodbus.constants import Endian
from pymodbus.payload import BinaryPayloadBuilder, BinaryPayloadDecoder


_logger = logging.getLogger()
ORDER_DICT = {"<": "LITTLE", ">": "BIG"}
```

[aritakku]

Tried again, and the installation via instructions does not work:

Otherwise you can pull the trunk source and install from there:

git clone git://github.com/riptideio/pymodbus.git
cd pymodbus
pip install -r requirements.txt

However, I tried my luck with another URI:

(new_virtual_env) root@vadelma:/home/pi# git clone https://github.com/pymodbus-dev/pymodbus.git
Cloning into 'pymodbus'...
remote: Enumerating objects: 13511, done.
remote: Counting objects: 100% (363/363), done.
remote: Compressing objects: 100% (193/193), done.
remote: Total 13511 (delta 208), reused 296 (delta 169), pack-reused 13148
Receiving objects: 100% (13511/13511), 7.72 MiB | 2.13 MiB/s, done.
Resolving deltas: 100% (9647/9647), done.

I will try to follow the installation instructions again.

[alexrudd2]

Tried again, and the installation via instructions does not work:

Otherwise you can pull the trunk source and install from there:
git clone git://github.com/riptideio/pymodbus.git

Apologies, this was an oversight when the organization was renamed. (#1291). You found the correct git URL.

However, as janiverson pointed out you forgot to run the following, which would have installed pyserial
pip install -r requirements.txt

[aritakku]

Installation process was (more) successful, followed the steps defined here ( https://pymodbus.readthedocs.io/en/latest/readme.html ).

I am unsure where the virtual environment should point to. Instructions used python3 -m venv /path/to/new/virtual/environment but the following step utilized .venv so I used command python3 -m venv .venv (at /home/pi/pymodbus dir).

(.venv) root@vadelma:/home/pi/pymodbus# python ./testikoodi_test7.py
Traceback (most recent call last):
  File "/home/pi/pymodbus/pymodbus/client/serial.py", line 225, in connect
    self.socket = serial.serial_for_url(
AttributeError: module 'serial' has no attribute 'serial_for_url'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/pi/pymodbus/./testikoodi_test7.py", line 39, in <module>
    client.connect()
  File "/home/pi/pymodbus/pymodbus/client/serial.py", line 237, in connect
    except serial.SerialException as msg:
AttributeError: module 'serial' has no attribute 'SerialException'

So now at least the error has changed. :-P

[janiversen]

As documented you need so install pyserial.

[aritakku]

I appreciate the help so far. :-) Now running the script ends up with

Traceback (most recent call last):
  File "/home/pi/pymodbus/./testikoodi_test7.py", line 4, in <module>
    import RS485Ext
ModuleNotFoundError: No module named 'RS485Ext'

Here's the script:

from pymodbus.client import ModbusSerialClient
from pymodbus.pdu import ExceptionResponse
from pymodbus.exceptions import ModbusIOException
import RS485Ext
import struct
import time

def registersToIeeeFloat(i):
  return struct.unpack('f', bytes(
                                   [((x & 0xff00) >> 8) if y else (x & 0x00ff)
                                     for x in i[::-1]
                                     for y in [False, True]
                                   ]
                                 )
                      )[0]

def registersToIeeeFloatReverse(i):
  return struct.unpack('f', bytes(
                                   [((x & 0xff00) >> 8) if y else (x & 0x00ff)
                                     for x in i
                                     for y in [False, True]
                                   ]
                                 )
                      )[0]

def dataConverter(t, d):
  if t == 'F':
    return registersToIeeeFloat(d)
  elif t == 'RF':
    return registersToIeeeFloatReverse(d)
  else:
    raise Exception("Converter '{0}' is not supported".format(t))


class ModbusException(Exception):
  def __init__(self, resp):
    self.msg = str(result)

  def __str__(self):
    return self.msg

class ModbusRequestDefinition(object):
  def __init__(self, kind, unit, address, count, converter, label):
    self.kind = kind
    self.unit = unit
    self.address = address
    self.count = count
    self.converter = converter
    self.label = label

reqs = [
#  ModbusRequestDefinition(4, 0x2000, 2, 'F', '(ERR) Unavailable device'),
#  ModbusRequestDefinition(1, 0x2000, 4, 'F', '(ERR) Wrong register size'),
#  ModbusRequestDefinition(1, 0x2000, 2, 'F', 'Voltage'),
#  ModbusRequestDefinition(1, 0x2020, 2, 'F', 'Frequency'),
#  ModbusRequestDefinition(1, 0x2060, 2, 'F', 'Current'),
#  ModbusRequestDefinition('H', 3, 0x0004, 2, 'RF', 'Resistance Channel 1'),
#  ModbusRequestDefinition('H', 3, 0x000C, 2, 'RF', 'Temperature Channel 1'),
#  ModbusRequestDefinition('H', 3, 0x0014, 2, 'RF', 'Resistance Channel 2'),
#  ModbusRequestDefinition('H', 3, 0x001C, 2, 'RF', 'Temperature Channel 2'),
  ModbusRequestDefinition('D', 4, 0x0000, 1, '', 'Discrete Input'),
  ModbusRequestDefinition('I', 5, 0x0001, 1, '', 'Temperature'),
  ModbusRequestDefinition('I', 5, 0x0002, 1, '', 'Humidity'),
]


def getSerial():
  return RS485Ext.RS485Ext(port='/dev/ttyAMA0', baudrate=9600, stopbits=1,
                           timeout=1)

client = ModbusSerialClient(method='rtu')
client.socket = getSerial()
client.connect()

delay = 0.05
period = 0.5

while True:
  for req in reqs:
    try:
      time.sleep(delay)
      if req.kind == 'H':
        # print("Trying to read: {0} {1} {2}".format(req.address, req.count, req.unit))
        result = client.read_holding_registers(address=req.address,
                                               count=req.count,
                                               unit=req.unit)
        if type(result) in [ExceptionResponse, ModbusIOException]:
          raise ModbusException(result)
        print("{0}: {1:.2f}".format(req.label,
                                    dataConverter(req.converter,
                                                  result.registers)))
      elif req.kind == 'D':
        result = client.read_discrete_inputs(address=req.address,
                                             count=req.count,
                                             unit=req.unit)
        if type(result) in [ExceptionResponse, ModbusIOException]:
          raise ModbusException(result)
        print("{0}: {1!s}".format(req.label, result.bits))
      elif req.kind == 'I':
        result = client.read_input_registers(address=req.address,
                                             count=req.count,
                                             unit=req.unit)
        if type(result) in [ExceptionResponse, ModbusIOException]:
          raise ModbusException(result)
        print("{0}: {1}".format(req.label, result.registers))
    except ModbusException as e:
      print("ERROR when querying '{0}': {1!s}".format(req.label, e))
      if client.socket is None:
        print("renew socket")
        client.socket = getSerial()

  print("-------------")
  time.sleep(period)

client.close()

PS. I am unsure what script I should use in order to access the Raspberry Pi 4B Serial HAT, which is available in /dev/serial0 -> /dev/ttyS0 , but the test7.py seemed like a good one to try out.

[aritakku]

Google revealed the class in question:

import serial.rs485
import serial.serialutil
import ctypes

class RS485Ext(serial.rs485.RS485):
    def __init__(self, *args, **kwargs):
        super(RS485Ext, self).__init__(*args, **kwargs)
        self.writec = ctypes.cdll.LoadLibrary('writec.so')
        r = self.writec.init()

    def write(self, b):
        d = serial.serialutil.to_bytes(b)
        r = self.writec.writec(self.fileno(), d, len(d))
        return r

Unfortunately there are other errors now, so perhaps this example I found is nonworking.

[janiversen]

The testikoodi_test7.py is not from our examples ! We do not have any file called test7.

Please use our examples.

[aritakku]

What example would allow me to read values from Gavazzi EM340 energy meter? Device is available via /dev/ttyAMA0

#/home/pi/pymodbus/examples#  python -m serial.tools.list_ports
/dev/ttyAMA0
1 ports found

[janiversen]

client* examples, especially client_calls.py

but of course you need to adapt it to your needs.