b' ISO : An error occurred during recv TCP : Connection timed out'

[Momoben3434]

HI ALL,
Im using a Pi4 with snap7 python to read data from plc cyclicly.

I encountered this issue while i'm reading constantly values of the PLC in every 0.65 sec then doing some calculations.
Im a begginner on python and i would like to have some support understanding the error or guide me with documentations, examples. When the error occur i lose communication with PLC and i have to run py again.

im attaching the code of the app.

"""

"""

import snap7
from snap7 import types
from snap7.types import WordLen, S7Object, param_types
from snap7.common import ipv4, check_error, load_library
from snap7.util import*
import tkinter.filedialog
from time import sleep
import tkinter
import time
from datetime import datetime
from pywhatkit import send_mail
from credential import google_p
from snap7.exceptions import Snap7Exception
import ctypes
import gc
import logging
import struct
import time
import unittest
import platform
from datetime import datetime, timedelta, date
from multiprocessing import Process
from unittest import mock

import snap7
from snap7 import util
from snap7.common import check_error
from snap7.server import mainloop
from snap7.types import S7AreaDB, S7DataItem, S7SZL, S7SZLList, buffer_type, buffer_size, S7Object, Areas, WordLen

#Snap 7 functions parameters
db_number = 127
start_offset = 4004
bit_offset = 1
value = 1 # 1 = true | 0 = false
start_address = 13024 # starting address
length = 4 # double word

#variable init
sum = 0.0
test_completed = False
count = 0
hold_1 = 0
results_received = False
seconds = 0.0
volume_1 = 0.0
volume = 0.0
chassis_nr = ''
connect = False

call snap7 client function

plc = snap7.client.Client(lib_location='/usr/local/lib/libsnap7.so')

IP address, rack, slot (from HW settings)

plc.connect('10.19.123.66', 0, 1)
#Get plc is connected true or flase
plc_connected = plc.get_connected()

read plc state run/stop/error

state = plc.get_cpu_state()

print plc state

print(f'State :{state}')

def test_wait_as_completion_timeouted(self, timeout=0, tries=500):
# Cli_WaitAsCompletion
# prepare Server
area = Areas.DB
dbnumber = 1
size = 1
start = 1
data = bytearray(size)
wordlen, data = self.client._prepare_as_read_area(area, size)
pdata = ctypes.byref(data)
self.client.write_area(area, dbnumber, start, bytearray(data))
# start as_request and wait for zero seconds to try trigger timeout
for i in range(tries):
self.client.as_read_area(area, dbnumber, start, size, wordlen, pdata)
res = None
try:
res = self.client.wait_as_completion(timeout)
check_error(res)
except RuntimeError as s7_err:
if not s7_err.args[0] == b'CLI : Job Timeout':
self.fail(f"While waiting another error appeared: {s7_err}")
# Wait for a thread to finish
time.sleep(0.1)
return
except BaseException:
self.fail(f"While waiting another error appeared:>>>>>>>> {res}")

    self.fail(f"After {tries} tries, no timout could be envoked by snap7. Either tests are passing to fast or"
              f"a problem is existing in the method. Fail test.")

def test_check_as_completion(self, timeout=5):
# Cli_CheckAsCompletion
check_status = ctypes.c_int(-1)
pending_checked = False
# preparing Server values
data = bytearray(b'\x01\xFF')
size = len(data)
area = Areas.DB
db = 1
start = 1
self.client.write_area(area, db, start, data)

    # start as_request and test
    wordlen, cdata = self.client._prepare_as_read_area(area, size)
    pcdata = ctypes.byref(cdata)
    self.client.as_read_area(area, db, start, size, wordlen, pcdata)
    for _ in range(10):
        self.client.check_as_completion(ctypes.byref(check_status))
        if check_status.value == 0:
            self.assertEqual(data, bytearray(cdata))
            break
        pending_checked = True
        time.sleep(1)
    else:
        self.fail(f"TimeoutError - Process pends for more than {timeout} seconds")
    if pending_checked is False:
        logging.warning("Pending was never reached, because Server was to fast,"
                        " but request to server was successfull.")

def readBool(db_number, start_offset, bit_offset):
reading = plc.db_read(db_number, start_offset, 1)
a = snap7.util.get_bool(reading, 0, bit_offset)
#print('DB Number: ' + str(db_number) + ' Bit: ' + str(start_offset) + '.' + str(bit_offset) + ' Value: ' + str(a))

        return str(a)

def readMemory(start_address,length):

        reading = plc.read_area(snap7.types.Areas.MK, 0, start_address, length)
        value = struct.unpack('>f', reading)  # big-endian
        #print('Start Address : ' + str(start_address) + ' Value: ' + str(value))
        #print('Value: ' + str(value))

        return (value)

def writeMemory(start_address,length,value):
plc.mb_write(start_address, length, bytearray(struct.pack('>f', value))) # big-endian
plc.disconnect()
print('Volume to PLC:' + str(value))

def append_new_line(file_name, text_to_append):
"""Append given text as a new line at the end of file"""
# Open the file in append & read mode ('a+')
with open(file_name, "a+") as file_object:
# Move read cursor to the start of file.
file_object.seek(0)
# If file is not empty then append '\n'
data = file_object.read(100)
if len(data) > 0:
file_object.write("\n")
# Append text at the end of file
file_object.write(text_to_append)

def tic():
global _start_time
_start_time = time.time()

def tac():
t_sec = round(time.time() - _start_time)
(t_min, t_sec) = divmod(t_sec,60)
(t_hour,t_min) = divmod(t_min,60)
print('Time passed: {}hour:{}min:{}sec'.format(t_hour,t_min,t_sec))

def sendmail(message_to_send):

send_mail (
    email_sender = "[email protected]",
    email_receiver = ("[email protected]","[email protected]"),
    message = message_to_send ,
    password = google_p['password'],
    subject = "Alert ! Primer Zone 4 - Volume is too low !!"
           )
print("Mail sent")

def disconnect(self) -> int:
"""Disconnect a client.
Returns:
Error code from snap7 library.
"""
logger.info("disconnecting snap7 client")
result = self.library.Cli_Disconnect(self.pointer)
check_error(result, context="client")
return result

Write results to a file.

file_name = tkinter.filedialog.askopenfilename()
#Write reject results to a file
reject_filename = tkinter.filedialog.askopenfilename()

while(True):

#Check the plc is connected 
#if plc_connected :


if not plc.get_connected():
    try:
        
        plc = snap7.client.Client(lib_location='/usr/local/lib/libsnap7.so')
        plc.connect('10.19.123.66', 0, 1)             
        
    except Snap7Exception as e:
        logger.error("warning in PLC connection >>{}".format(e))
        connect = False
        continue
    
else:
        
    
        #get string test
        data = plc.db_read(db_number=127, start=4014, size=8)
        
        # read the trigger from PLC
        read_start_req = readBool(127,4004,1)
    
        # time stamp 
        now = datetime.now()

        if read_start_req == 'True':

            results_received = False

            # readings reading 
            for x in readMemory(13024,4):
                time.sleep(0.65)
                count = count + 1
                my_results = x
                sum = sum + my_results
                print(count)
                print('Readings :' + str(my_results) )
                print('sum:' + str(sum))               

        else:

            # Sum of the readings 
            if count > 0 and not results_received:
                # compensation factor.12.522 ml
                
                # Volume calculation
                volume = sum /60
    
                #Dentsity beta 5404 is 0.9
                weight = volume * 0.90

                #results time stamps 
                timestamp = datetime.timestamp(now)
                dt_object = datetime.fromtimestamp(timestamp)
                
                if str(snap7.util.get_string(data, 0)) == '':
                    chassis_nr = 'NO RFID DATA'
                else:
                    chassis_nr = str(snap7.util.get_string(data, 0))

                    #Display results to the user 
                print('Job Number:'+" "+ chassis_nr +" "+','+ 'Volume Dispensed is :'+" "+ str(volume)+ " " + '(ml)'+" " + '/' + str(weight) +'(g)')                    
                print(str(sum))
                contents = ("Job Number:"+"\n"+ chassis_nr + " " + "\n" + "Volume Dispensed:" + "\n" + str(volume)+" "+ '(ml)' + "\n" + "Time Stamp :" "\n" + str(dt_object))

                #Update the file with the results (append)
                append_new_line(file_name, contents)

                #Write the volume to te PLC
                writeMemory(4010,4,volume)
                
                #send mail to process team 
                if volume <= 0.3 or volume == 0.0:
                    sendmail(contents)
                    #Update the file with the results (append )
                    append_new_line(reject_filename, contents)                               
                
                results_received = True
                
                # Close connection 
                plc.disconnect()
                time.sleep(10)
                print('plc connect ', connect)
                
                #Init the variables 
                count = 0
                volume = 0.0
                volume_1 = 0.0
                sum = 0.0               

            else :

                hold_1 = hold_1 + 1

                if hold_1 < 1:
                    
                        print('...')
                        results_received = False

---

Error :
b' ISO : An error occurred during recv TCP : Connection timed out'
Traceback (most recent call last):
File "/home/momo3434/Desktop/PyProject/primer/python/snap7_/zone4_primer_1.py", line 231, in
read_start_req = readBool(127,4004,1)
File "/home/momo3434/Desktop/PyProject/primer/python/snap7_/zone4_primer_1.py", line 136, in readBool
reading = plc.db_read(db_number, start_offset, 1)
File "/usr/local/lib/python3.9/dist-packages/snap7/client.py", line 226, in db_read
check_error(result, context="client")
File "/usr/local/lib/python3.9/dist-packages/snap7/common.py", line 89, in check_error
raise RuntimeError(error)
RuntimeError: b' ISO : An error occurred during recv TCP : Connection timed out'

[swamper123]

To much code - won't read everything.
As well, you should take a look how to quote Code in Github Markdown, so that stuff is more readable. ;)

For the start, I wouldn't use asynchroun functions/methods, since this would be the next step (especially if you want to profit from it on Python side...) about handling async PLC-requests with asynchrounus Python. So stay there on synchrounus side first.

We got some examples mostly below every function, like:

python-snap7/snap7/client.py

Line 366 in 38d6576

def read_area(self, area: Areas, dbnumber: int, start: int, size: int) -> bytearray:

Are you excepting such problems?
Are cou disconnection clearly, if sth like that happens and try a reconnect?

Have you traced the package flow (e.g. with Wireshark)?
Do you receive an answer from the PLC?

[Momoben3434]

Thank you for your reply.
I will quote the code as per your suggestions and read about asynchronous functions then I will feedback.

‘The error is happening in different occasions :
1- disconnecting the data cable of the port. For testing purposes.
2- While reading the DB.
The code can hold for a good 2 hours without crashing , then suddenly the error occurring.

Again much appreciated.

[spreeker]

Hi Momben,

Well to debug your code I would cut the problem in small pieces. Try to reproduce errors in small pieces of your code.

1. Only run the code with the loop printing the extracted value. Does the crash still occur? Can the code run for days now? 0.65 ms loop is pretty fast. Connection problems will occur and your code needs to handle that.

2. Doing concurrent stuff in python is very very hard to get right. It is easier to have a bunch of python scripts with single loops sharing state via a database, redis or zeromq. It's cleaner to. Python cannot really run multiple stuff concurrent and it is just kind of 'faked'. (GIL) global interpreter lock.

3. looks like some python code is blocking, and putting sleeps in your code is a big code smell IMHO. sending an email can take much longer then 0.65 seconds for example.

[Momoben3434]

Thanks man. I’m trying to improve the code as I mentioned before I’m a beginner into Python but I luv this programming language . The code can run for 3 - 4 before crashing ( communication is done via PI4 via WiFi with the PLC ) my code structure is done as SCL programming ! So multiple uses of if .. the 0.6s reading is actually needed for accuracy of the reading of the Analog input readings. Any help is much appreciated or advices .
thank you dude,

[Momoben3434]

Hi All,
Thank you for the information and support.
I have managed to solve the issue basically i was opening to many connection with PLC , and the fundamentals of snap7 is to open 1 connection at the time.
NOW i'm taking data cyclically in 0.65 with no issues at the end of the process i disconnect the client.
running for more than 3 days with no interruption.

THank you again

[AlexL4nda]

Use "try" and "except" to avoid your code stops when an error occur