Arduino send WOL message

Projects Networking, Protocols, and Devices
1

hey guys

I try to send a Wake on LAN "Magic Packet" with my Arduino Ethernet. This "Magic Packet" is quite easy, 6 x "0xff" then 16 x the mac address, so the payload should be 102 bytes (raw data, without headers). My captured packet is only 38 bytes large, I guess the SENDING buffer is limited.

Here is the code I use:

byte broadcastAddress[] = { 255, 255, 255, 255 };    //to verify!

//send wol magic pajet
void WOL(byte mac[]) {
#ifdef USE_SERIAL_DEBUG
  Serial.print("Send WOL... ");
#endif 
  
    byte i;
    //Starts a connection to write UDP data to the remote connection, parameter: remoteIP, remotePort
    //Hint about port 7: Since the magic packet is only scanned for the string above, and not actually 
    //parsed by a full protocol stack, it may be sent as any network- and transport-layer protocol, although 
    //it is typically sent as a UDP datagram to port 7 or 9
    Udp.beginPacket(broadcastAddress, 7);
    
    //Writes UDP data to the remote connection. Must be wrapped between beginPacket() and endPacket().

    //Start of WOL magic paket (preamble)
    for (i=0; i<6; i++) {
      Udp.write(0xff);
    }
    
    //the wol packet contains 16 times the mac address
    //NOTE: BUG here, we cannot send more than 46 bytes...
    for (i=0; i<16; i++) {
      Udp.write(mac, sizeof mac);
    }
    
    //Called after writing UDP data to the remote connection.
    Udp.endPacket();
#ifdef USE_SERIAL_DEBUG
  Serial.println("done!");
#endif 
    
}

I took a look at the EthernetUDP class, all I found was a

#define UDP_TX_PACKET_MAX_SIZE 24

which is a bit unrelated I guess. Can someone help me?

Cheers

2

Have you checked the contents of the packet that is being sent?
From hte code you posted I can't see how sizeof can return the size of 6 bytes for the mac address as it can only see that it is a byte array that is passed in. Check that size of is giving the right value.

I'm thinking that sizeof may be giving you a sizeof the pointer which I am assuming is 2 bytes on the Arduino.

Paul

3

Michu,

I used the following code to do what you're trying to do - http://www.blueleafsoftware.com/Resources/EmbeddedSand/Wake_on_LAN

Hope it helps.