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UDP Broadcast using the CCS Ethernet development board

 
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Greg Richter



Joined: 15 Feb 2008
Posts: 7
Location: Ellijay, GA

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UDP Broadcast using the CCS Ethernet development board
PostPosted: Fri Feb 15, 2008 1:14 pm     Reply with quote

Nice piece of code, with a little gotcha for UDP broadcast in UDP.C round about line 165:

// If remoteNode is supplied, remember it.
if ( remoteNode )
{
memcpy((void*)&p->remoteNode,
(void*)remoteNode,
sizeof(p->remoteNode));
}
// else Set broadcast address - TO BE DONE */

Oh, bother ... You can either modify the library code, or simply put:

RemoteNode.MACAddr.v[0] = 0xFF; // remote broadcast node
RemoteNode.MACAddr.v[1] = 0xFF;
RemoteNode.MACAddr.v[2] = 0xFF;
RemoteNode.MACAddr.v[3] = 0xFF;
RemoteNode.MACAddr.v[4] = 0xFF;
RemoteNode.MACAddr.v[5] = 0xFF;

RemoteNode.IPAddr.v[0] = 255;
RemoteNode.IPAddr.v[1] = 255;
RemoteNode.IPAddr.v[2] = 255;
RemoteNode.IPAddr.v[3] = 255;

... in your code to enable UDP broadcast. Truly a minor tweak, but it chewed up half a day chasing it down. If you're doing UDP broadcast with this library, this'll save you some time. Works beautifully, now.

-Greg
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asmallri



Joined: 12 Aug 2004
Posts: 1551
Location: Perth, Australia

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PostPosted: Fri Mar 07, 2008 10:10 am     Reply with quote

The MAC address is fine. The IP layer address broadcast may or may not work depending on the stack implementation of the intended remote node. It also will not transit a router. A subnet broadcast can be used instead.

Let's say your target is on on subnet 192.168.1.0 with a mask of 255.255.255.0 then the broadcast address for the subnet is 192.168.1.255 - you can reach this from the local subnet or from behind a router.
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