CODESYS Forge - CODESYS Forge / Talk / Engineering 🇬🇧: UPDPeer Sends only the first packet

Hello. I'm having an issue with UDPPeer. The instrument I'm trying to communicate with sends one response packet per request (until I request streaming data, which I haven't gotten that far yet). Using the code below, I can send and receive the first packet, but only the first one. It won't send a 2nd packet. Using Wireshark, I can see that the 2nd packet never leaves the PLC. I noticed that UDPSend.XDone always stays high after the first send. I tried changing up the code to disable and re-enable the UDPPeer connection for every send/receive, but that didn't help.

Please excuse my primitive coding skills.

Thanks,
Jim

FUNCTION_BLOCK FB_Instrument
VAR_INPUT
   sInstrumentIP: STRING := '192.168.12.80'; // IP address of Instrument
   arrbyInstrumentSendData : ARRAY [0..17] OF BYTE := [16#AB, 16#CD, 16#0, 15(16#0)];
   xInstrumentSendNow : BOOL;
   xInstrumentInit: BOOL;
END_VAR
VAR_OUTPUT
   arrbyInstrumentReceiveData : ARRAY [0..87] OF BYTE := [88(16#0)];
   xInstrumentSndRcvComplete : BOOL := FALSE;
   xInstrumentSndRcvError : BOOL := FALSE;
   eInstrumentSndRcvErrorCode: STRING;
   iInstrumentPacketsReceived: CAA.COUNT;
END_VAR
VAR
   iState: INT:= 0;
   IPAddress : NBS.IP_ADDR; (* IP Address *)
   uiPort : UINT; (* Port No. *)
   ctRecAnswers : CAA.COUNT; (* No. of received messages *)
   UDPPeer : NBS.UDP_Peer; (* FB UDP Peer *)
   XUDPPeer : NBS.UDP_Peer; (* FB UDP Peer *)
   UDPSend : NBS.UDP_Send; (* FB UDP Send *)
   UDPReceive : NBS.UDP_Receive; (* FB UDP Receive *)
   Peer : CAA.HANDLE; (* Handle to the peer connection *)
   xEnable : BOOL;
   sUDPData :STRING;
   uiRcvSize: UINT;
   iErrorCode : INT := 0;
   TON_WatchdogReceive: TON;
END_VARIF xInstrumentInit THEN 
   iState := 0;
END_IF;
CASE iState OF
0: // Initialize the connection
   
   IPAddress.sAddr := sInstrumentIP; // IP address of Instrument
   uiPort := 50000;
   xInstrumentInit := FALSE;
   TON_WatchdogReceive.PT := T#500MS;
   TON_WatchdogReceive.IN := FALSE;
   xInstrumentSndRcvComplete:= FALSE;
   xInstrumentSndRcvError:= FALSE;
   xEnable := TRUE; // Used for send case and for UDPPeer function call
   iState := 10;
   
10: // Wait for Send
   IF xEnable AND UDPPeer.xActive THEN 
      IF xInstrumentSendNow THEN
         // Clear variables for new send
         xInstrumentSndRcvComplete:= FALSE;
         xInstrumentSndRcvError:= FALSE;
   
         UDPsend (
            xExecute   := TRUE, 
            ipAddr   := IPAddress,
            uiPort   := uiPort,
            hPeer   := UdpPeer.hPeer,
            szSize   := 18,
            pData   := ADR(arrbyInstrumentSendData),
            udiTimeOut   := 1000000, (* usec *)
            );
         xInstrumentSendNow   := FALSE;
         iState:= 15;
      ELSE
         iState:= 10; // nothing to send, come back here
      END_IF;
   END_IF;
      
15: // Wait for send to complete or error
   IF UdpSend.xDone THEN
      UdpSend.xExecute := FALSE;      
      CASE arrbyInstrumentSendData[3] OF // Determine receive size based on Opcode request sent
         0..15: // Opcodes 16#0-16#F - Configuration data
            uiRcvSize := 18;
         16: // Opcode 16#10 - Stream Measurement Data
            uiRcvSize := 88;
         32: // Opcode 16#20 - Information
            uiRcvSize := 88;
      END_CASE
      // Start listening
      IF UDPPeer.xActive THEN
         UDPReceive(
            xEnable:= TRUE,
            hPeer:= Peer,
            szSize:= uiRcvSize, 
            pData:= ADR(arrbyInstrumentReceiveData)
            );
      END_IF;
      iState:= 20; // Wait for data 
      TON_WatchdogReceive.IN := TRUE; // Start watchdog
   END_IF;
   IF UdpSend.xError THEN
      UdpSend.xExecute := FALSE;
      iState:= 30; // Error state
   END_IF;
      
20: // Wait for data
   IF UDPReceive.xReady THEN
      UDPReceive.xEnable := FALSE;
      ctRecAnswers := ctRecAnswers + 1; // Number of UDP calls
      iState:= 10; // Data received, go back to wait to send
      xInstrumentSndRcvComplete := TRUE;
      TON_WatchdogReceive.IN := FALSE;
      iInstrumentPacketsReceived := ctRecAnswers;
   ELSIF UDPReceive.xError THEN
      UDPReceive.xEnable := FALSE;
      TON_WatchdogReceive.IN := FALSE;
      iErrorCode := UDPReceive.eError;
      iState:= 30; // Error state
   ELSIF TON_WatchdogReceive.Q THEN
      UDPReceive.xEnable := FALSE;
      xInstrumentSndRcvComplete := TRUE;
      TON_WatchdogReceive.IN := FALSE;
      iState:= 10; // Go back to wait for now. Improve handling later.
   END_IF;
30: // Error
   xInstrumentSndRcvError := TRUE;
   xInstrumentSndRcvComplete := FALSE;
   
40: // Exit
END_CASE
// Call the CAA FUNCTION
UDPPeer(xEnable:= xEnable, ipAddr:= IPAddress, uiPort:= uiPort, hPeer=> Peer);

To me it looks like you never call the function block UDPsend when you have execute set to false so it never registers the falling trigger. After you set UdpSend.xExecute := FALSE; you then need to call UDPsend(); before you go back into case statement 10 where it gets set back to TRUE.

For example:

15: // Wait for send to complete or error
   IF UdpSend.xDone THEN
      UdpSend.xExecute := FALSE;
      UDPsend();  (*********************** This is added *****************************)      
      CASE arrbyInstrumentSendData[3] OF // Determine receive size based on Opcode request sent
         0..15: // Opcodes 16#0-16#F - Configuration data
            uiRcvSize := 18;
         16: // Opcode 16#10 - Stream Measurement Data
            uiRcvSize := 88;
         32: // Opcode 16#20 - Information
            uiRcvSize := 88;
      END_CASE
      // Start listening
      IF UDPPeer.xActive THEN
         UDPReceive(
            xEnable:= TRUE,
            hPeer:= Peer,
            szSize:= uiRcvSize, 
            pData:= ADR(arrbyInstrumentReceiveData)
            );
      END_IF;
      iState:= 20; // Wait for data 
      TON_WatchdogReceive.IN := TRUE; // Start watchdog
   END_IF;
   IF UdpSend.xError THEN
      UdpSend.xExecute := FALSE;
      UDPsend();  (*********************** This is added *****************************)
      iState:= 30; // Error state
   END_IF;

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UPDPeer Sends only the first packet

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UPDPeer Sends only the first packet