Added Multicast UDP support

Fix #1531

Author: aallan

libraries/Ethernet/src/EthernetUdp.cpp

@@ -216,3 +216,37 @@ void EthernetUDP::flush()
   }
 }
 
+/* Start EthernetUDP socket, listening at local port PORT */
+uint8_t EthernetUDP::beginMulticast(IPAddress ip, uint16_t port)
+{
+  if (_sock != MAX_SOCK_NUM)
+    return 0;
+
+  for (int i = 0; i < MAX_SOCK_NUM; i++) {
+    uint8_t s = W5100.readSnSR(i);
+    if (s == SnSR::CLOSED || s == SnSR::FIN_WAIT) {
+      _sock = i;
+      break;
+    }
+  }
+
+  if (_sock == MAX_SOCK_NUM)
+    return 0;
+
+  // Calculate MAC address from Multicast IP Address
+  byte mac[] = {  0x01, 0x00, 0x5E, 0x00, 0x00, 0x00 };
+
+  mac[3] = ip[1] & 0x7F;
+  mac[4] = ip[2];
+  mac[5] = ip[3];
+
+  W5100.writeSnDIPR(_sock, rawIPAddress(ip));   //239.255.0.1
+  W5100.writeSnDPORT(_sock, port);
+  W5100.writeSnDHAR(_sock,mac);
+
+  _remaining = 0;
+  socket(_sock, SnMR::UDP, port, SnMR::MULTI);
+  return 1;
+}
+
+

libraries/Ethernet/src/EthernetUdp.h

@@ -53,6 +53,7 @@ class EthernetUDP : public UDP {
 public:
   EthernetUDP();  // Constructor
   virtual uint8_t begin(uint16_t);	// initialize, start listening on specified port. Returns 1 if successful, 0 if there are no sockets available to use
+  virtual uint8_t beginMulticast(IPAddress, uint16_t);	// initialize, start listening on specified port. Returns 1 if successful, 0 if there are no sockets available to use
   virtual void stop();  // Finish with the UDP socket
 
   // Sending UDP packets