Connectionless Ethernet library

Forum 2005-2010 (read only) Software Bugs & Suggestions
1

The Ethernet library dearly needs a way to send packets without connecting a Client.

I would specifically want to send Wake-On-LAN magic packets - a UDP datagram would work just fine, but there's currently no high-level way to send anything to remote hosts that obviously aren't there to respond...

2

Check out this thread, which points to this site.

haven't tried it myself (yet).

I would be interested in seeing your WoL code, if you feel like sharing.

-j

3

Thanks for the hint - looks pretty straightforward, unfortunately it seems to consume resources and might not fit into my already crammed application...

I'll probably need to try it as a proof of concept anyway, I will then post the code :slight_smile:

4

OK - I actually didn't use any of that UDP wrapper code, since all it does is wrap... The minimal code to send a WOL packet, assuming we live in subnet 10.0.0.x/24:

extern "C" {
#include "utility/types.h"
#include "utility/w5100.h"
#include "utility/socket.h"
}
#include <Ethernet.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = { 10, 0, 0, 111 };

void setup() {
Ethernet.begin(mac, ip);
}

void loop() {
uint8_t socket_index = 0;
uint8_t txbuf[102]; /* Size of magic packet = 6 + 16*6 */
uint8_t p;
byte n, i;
uint8_t remote_ip[] = {10, 0, 0, 255}; / Broadcast address /
uint8_t remote_mac[] = {0x00, 0x0e, 0x2e, 0x0a, 0x23, 0x19}; / Remote's MAC */

/* Use 9999 as source port, shouldn't be of any relevance */
socket(socket_index, Sn_MR_UDP, 9999, 0);

/* Magic packet is 6 * 0xff followed by 16 times the destination MAC */
p = txbuf;
for(n = 0; n < 6; n++) p++ = 0xff;
for(n = 0; n < 16; n++) {
for(i = 0; i < 6; i++) p++ = remote_mac;

  • }*
    /* Send to remote_ip and port 0 (port doesn't matter) /
    sendto(socket_index, txbuf, 6 + 616, remote_ip, 9999);
  • close(socket_index);*
  • for(;;);*
    }
    The sad part here is that this can't really coexist with the normal Ethernet code during the time it is actually used, since we run over it - e.g. Server.begin() allocates all of the four sockets W5100 offers us, and so socket 0 used above is not free anymore then. That UDP example code linked previously in this topic has the same problem, though.
    I only tested this with one remote, and for some peculiar reason it really needed this packet to be sent to the broadcast IP address. As far as I understand, it should not matter since the NIC - which does all the work while the host system sleeps - doesn't even know its IP address when it receives the WOL packet.
5

for some peculiar reason it really needed this packet to be sent to the broadcast IP address.

Isn't that part of the specification for how WoL works?

--Phil.

6

Yes, you're right - but for some reason the helper program I've used to send WOL packets (wolcmd.exe) worked just fine using a single IP as destination address. I guess it sets the broadcast bit anyway.

But still, I would like to see further development on the Ethernet library, it's quite rudimentary as it is now (how do you shut down a server, for example?) :slight_smile: But I guess this is a hard task, it uses a large part of the sketch space already...