Simulink-Python Simultaneous Send-Receive using TCP-IP

I wanna send/receive data from Python (inside Visual Components software) to Simulink using TCP-IP. I have two parts of code, one for sending and other for receiving.

When I use only send part or receive part, it works! But when I try to use them both, sending and receiving at the same time, I get error in Simulink like connection refused etc and upon re-running, the Simulink displays the received data. Also I don't receive the data in Python when using both at the same time.

So how to solve it and send/receive data at the same time?

Screenshot of Simulink is attached. Python code is below.

   from vcScript import *
    import socket
    import struct
    def OnRun():

      #Server TCP Communication
      TCP_IP = '127.0.0.1'
      TCP_PORT = 5002
      BUFFER_SIZE = 20  # Normally 1024, but we want fast response

      s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      s.bind((TCP_IP, TCP_PORT))
      s.listen(1)

      conn, addr = s.accept()
      print 'Connection address:', addr
      while 1:
          data = conn.recv(BUFFER_SIZE)
          if not data: break
          print "received data:", data
          conn.send(data)  # echo
      conn.close()

      #Send to Simulink
      serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
      serversocket.bind(('localhost',30001))
      serversocket.listen(5)
      (clientsocket, address) = serversocket.accept()
      for i in range(50):
        msg1 = struct.pack('>d', 1.1+i)
        delay(0.2)
        clientsocket.send(msg1)
      clientsocket.close()

Answer 1

[Thomas Hafkamp]

Your code probably doesn't work because you didn't specify the Block priorities correctly.

According to this Simulink tutorial, for some reason Simulink needs to send a TCP/IP message first before receiving a TCP/IP message. To do so, you need to set the priority of the TCP/IP Send block to 1 and of the TCP/IP Receive block to 2:

"Step 8: Specify the Block Priorities To run the simulation correctly, specify the order in which Simulink should process the blocks. Right-click the block and select Properties. Enter the priority number in the Priority field. In this case, set the priority of TCP/IP Send to 1 and TCP/IP Receive to 2."

In the tutorial, a MATLAB tcpip echo server is used. However, when using Python as the echo server with the code below, I found out that the order should be reversed. So first Simulink needs to receive, and then Simulink needs to send.

Simulink scheme:

This Simulink scheme runs for 4.9 [s] with a fundamental sample time of 0.1 [s]. A linear ramp with slope 10 [1/s] is sampled. This way, the values 0 to 49 are sent to Python.

Python code:

import socket, struct

TCP_IP = 'localhost'
TCP_PORT = 30001
BUFFER_SIZE = 1024

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((TCP_IP, TCP_PORT))
print('Waiting for Simulink to start')
s.listen(1)

conn, addr = s.accept()
print('Connection address: ', addr)

for i in range(50):
    # send data to Simulink
    msg1 = struct.pack('>d', i)
    conn.send(msg1)
    print('sent data:', i)
    
    # receive data from Simulink
    data = conn.recv(BUFFER_SIZE)
    converteddata = int.from_bytes(data, byteorder='big', signed=False)
    print('received data:', converteddata)

conn.close()

[Soumil Chugh]

I am trying to run a simulation model in MATLAB which takes input via TCP/IP from python code and sends back some data to the python code. I am unable to sync both the times. My TCP/IP is sending data with a different time interval(0.02) while my simulation model runs with a different interval(0.08). I tried to fix the step size in simulation model configuration but nothing helps. Can anybody explain the same?