Connection Refused to Simulink Real Time Target Port

Hi,

I am trying to use sockets (socketfuncs.h) on a Simulink Real-Time R2017b target in a C S-function.

I got a client socket to run and send some data to a server.

In the next stept I want to open a listening socket (server) and accept incoming connections and read data, if there is any. The server socket is running as non blocking. In the mdlOutput() function I use the accept() function to repeatedly look for incoming connections.

When I run this server and try to connect with a tcp client (telnet for example), I get a connection refused error. TCP error 10061. I tried different Ports in the range of 20000-33000, 80. The firewall is disabled.

I wanted to check which ports are open on the SLRT target, but I could not figure out how to do it.

/*** GLOBAL VARIABLES ***/ 
SOCKET ClientSocket = 0;
SOCKET ServerSocket = 0;
bool ConnReady = false;

uint_T localPort = 32000;
uint_T targetPort = 20000;
char_T targetAddress[16] = "192.168.8.13";    

static void mdlOutputs(SimStruct *S, int_T tid)
{ 
      char message[2500];
      char server_reply[2000];
      int recv_size = 0;

        SOCKET _acceptSocket;

  // Prepare data to send
  sprintf(message, "Hallo! Ich bin ein SLRT Tcp/Ip Client.\n");
      
    //Send some data    
    if( send(ClientSocket, message , strlen(message) , 0) < 0)
    {
        printf("Send failed\n");           
  }

  // SERVER: Check for incoming data
  if (!ConnReady)
    _acceptSocket = accept(ServerSocket, NULL, NULL);

  int bytesSent;
  int bytesRecv = SOCKET_ERROR;
  char recvbuf[200] = "";
  char sendbuf[200] = "";

  if (_acceptSocket != INVALID_SOCKET)
  {
    ConnReady = true;
    ServerSocket = _acceptSocket;
  }

  if (ConnReady)
  {
    bytesRecv = recv(ServerSocket, recvbuf, 200, 0);

    if (bytesRecv == SOCKET_ERROR)
      printf("Server: recv() error %ld.\n", getlasterror());
    else
    {
      printf("Bytes received: %ld, Received data is: \"%s\"\n", bytesRecv, recvbuf);
    }
  }
  else
    printf("accept failed: %d.", getlasterror());
}

Also, there seems to be an offset in the errors reported from the socketfuncs.h functions. For example accept() returns 112. Though 112 is not defined in socketfuncs.h, I can see that

#define EDESTADDREQ 12 /* destination address is required / #define RTIP_ERRNO 100 / RTIP error number offset */

So it is safe to assume that I always have to substract RTIP_ERRNO from getlasterrror when using socketfuncs?

Thanks alot.

Answer 1

[Jon Lobo]

It's not recommended to do this through an S-Function. I recommend using the TCP blocks here: https://www.mathworks.com/help/xpc/tcp.html

[Paul Stansell]

link is dead

[Diego Kuratli]

R2020a and previous: https://www.mathworks.com/help/releases/R2020a/xpc/tcp.html

R2020b and newer: https://www.mathworks.com/help/slrealtime/tcp.html