Receive UDP Packets via Port.Receive

2020-02-27T13:47:58.387000Z

Didn't try your code, but I had good luck with the following FBs of Net Base Services:

NBS.UDP_Peer
NBS.UDP_Send
NBS.UDP_Receive

I think Net Base Services is build around on the UDP library. Don't know if you are supposed to use UDP directly. NBS was quite straight forward for me.

Receive UDP Packets via Port.Receive

2020-02-27T13:47:58.242000Z

Hey there,

I've been trying to receive UDP packets with the UDP library (can be found in CAA Net Base Services) for quiet a while now, but I don't seem to get to a result. First of all, here's the code I'm working with.

PROGRAM PLC_PRG
VAR
   state :INT := 0;                        // State of the SM
   driver : UDP.UDPDriver;                     // UDP Driver
   port : UDP.Port;                           // UDP Port
   
   (* The following parameters describe the socket on the SPS *)
   src_ipAddr_ud : UDINT;                     // Source IP-Address as UDINT
   src_ipAddr_st : STRING := '192.168.200.99';         // Source IP-Address readable
   src_Port : UINT := 5005;                     // Source Port
   
   (* The following parameters describe the destination for outgoing packets *)
   dest_ipAddr_ud : UDINT;                     // Destination IP-Address as UDINT
   dest_ipAddr_st : STRING := '192.168.200.165';         // Destination IP-Address readable
   dest_Port : UINT := 5005;                     // Destination Port
   
   result : SysTypes.RTS_IEC_RESULT;               // Result of receive function 
   bind : UDINT;                           // Result of binding
   resultCreate : SysTypes.RTS_IEC_RESULT;            // Result of creating the port
   rcvData : ARRAY[0..99] OF BYTE;               // Data which was received 
   sendData : STRING := 'Hello World';               // Data to be sent
   
   END_VAR

CASE state OF
   0:   // Initial State
      resultCreate:=driver.CreatePort(ADR(port));      
      state:=10;
   10:   // Bind Socket
      src_ipAddr_ud:=UDP.IPSTRING_TO_UDINT(sIPAddress:=src_ipAddr_st);
      port.IPAddress := src_ipAddr_ud;
      port.ReceivePort := src_Port;
      port.SendPort := dest_Port;
      bind := port.Bind(udiIPAddress:=src_ipAddr_ud);
      state:=20;
   20: // Send packet
      dest_ipAddr_ud := UDP.IPSTRING_TO_UDINT(sIPAddress:=dest_ipAddr_st);
      port.Send(udiIPTo:=dest_ipAddr_ud, pbyData:=ADR(sendData), diDataSize:=SIZEOF(sendData), uiPortTo:=dest_Port);
      state:=30;
   30:
      result := port.Receive(pbyData:=ADR(rcvData), diDataSize:=SIZEOF(rcvData));
      IF result<>ERRORS.ERR_PENDING THEN
         state := 40;   
      END_IF
      
   40: // Placeholder
   
END_CASE

Sending a packet works perfectly fine with that code. Using a python script on the receiver side (the IP participant with the IP Address 192.168.200.165 - let's call him 165 from here on) I receive the string "Hello World". However, the receive function on Codesys doesn't really seem to work.
With a python script I was able to send a simple byte from 165 to my machine. Tracking it with Wireshark was successfull, so it definitely arrived at my computer. The ressource monitor of Windows also lists IP 192.168.200.99, Port 5005 as reserved port for Codesys with no constraint from the firewall. When I use a python script on my computer which simply receives UDP packets, I even receive the packet with this. Still, the Codesys Receive-Function returns with ERR_PENDING.

Does anybody have any idea what I could have possibly missed?

By the way, I have been trying this with the SysSocket library as well and I again got all the way to the point where I want to receive a packet - with that library one can even check whether binding a socket was succesfull and according to Codesys it was - but I just don't receive it.

Grateful for your help,
Alex

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