udpStartListen (Function)

This starts to listen for data received as a connectionless UDP packet on the specified local port.

The data will then be received with the updReceive function block.

Note: many GSM networks are using a firewall so that inbound connections to the RTCU are blocked when using the Cellular network interface.

Input:

port : DINT

Port number listening on.

rip : DINT

Remote IP address accepted. 0 = all IP addresses accepted (default).

iface : SINT (default 0)

The network interface to listen on. 0 = all networks (default), 1 = Cellular network, 2 = LAN network, etc. (See Network)

Returns: SINT

ID for the connection or 0 if an error occurred (out of resources).

Declaration:

FUNCTION udpStartListen : SINT;
VAR_INPUT
   port  : DINT;      // Port number to listen on
   rip   : DINT :=0;  // Accept from this remote IP only. 0=all.

   iface : SINT :=0;  // Interface to listen on
END_VAR;

Example:

INCLUDE rtcu.inc
 
PROGRAM udp_server;
VAR
   fbReceive : udpReceive;            // Receive data on a UDP socket
   port      : INT := 2500;           // port to receive data on
   udp_id    : SINT;                  // listener ID
   host      : STRING;                // translated IP
   line      : STRING;                // ASCII string to send
   data      : ARRAY[1..255] OF SINT; // received data buffer
   rc        : INT;                   // return code of command
END_VAR;
 
gsmPower(power := ON);
gprsOpen();
 
// Wait for the cellular connection to be established
WHILE NOT gprsConnected() DO 
   DebugMsg(message := "Waiting for cellular connection");
   Sleep(delay := 2500);
END_WHILE;
 
// Listen for incoming connection on a UDP port
udp_id := udpStartListen(port := port, rip := 0);
BEGIN
   // update udp received data
   fbReceive(id := udp_id, data := ADDR(data), maxsize := SIZEOF(data));
 
   IF fbReceive.ready THEN
      host := sockIPToName(ip := fbReceive.ip);
      DebugFmt(message := "Received '\1' bytes from '" + host + "'", v1 := fbReceive.size);
      line := strFromMemory(src := ADDR(data), len := fbReceive.size);
      DebugMsg(message := "Message : " + line);
   END_IF;
END;
END_PROGRAM;