Multicast UDP socket

TCP/IP Chip W5500
1

I would like to open a UDP socket that sends data to a multicast group and receives unicast messages.

My current configuration is to open a UDP socket with:

socket(4, Sn_MR_UDP, 2222, SF_BROAD_BLOCK);

and send the data with

sendto( 4, *message_buffer, message_length, multicastAddr, 2222);

The problem is that, although the multicast address is correct, the destination MAC address is the MAC address of the receiving device, not the multicast hardware address.

2

W5500 Broadcast Server - TCP/IP Chip / W5500 - WIZnet Developer Forum maybe this will help?

3

I don’t see the destination hardware address being configured in the code in the provided link. Also, I think my situation is slightly different than that post. They were trying to receive multicast/broadcast frames with the W5500; I am trying to send multicast frames and receive unicast frames with W5500

Does the destination hardware address automatically get updated when I pass the multicast IP address to the sendto() function?

Specifically, I am trying to send to 239.192.8.32 multicast group; the destination hardware should be updated to multicast address but right now it is filled with the receiver’s MAC address

4

Look at the W6100 datasheet chapter 6.3.3, this may give some good idea.
It seems MC must not have ARP done, therefore try using SEND_MAC.

5

In chapter 6.3.3, it looks like I have to set the appropriate DHAR register myself.

In this multicast example provided by WIZnet, they never set DHAR, I am not sure how this works: https://github.com/Wiznet/ioLibrary_Driver/blob/master/Application/multicast/multicast.c

Also in the W5500 datasheet section 4.2, for multicasting in UDP mode, it says to set Sn_DIPR & Sn_DPORT, it does not say anything about Sn_DHAR.