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how to enable LWIP multicast reception on STM32F7 + FreeRTOS?

Question asked by Kamil Alkhouri on May 20, 2018

I have a client/server LWIP program that works correctly with unicast communication however I want to use multicast features so I used IGMP library did the following:

1- in opt.h:
#define LWIP_IGMP 1 //allowed IGMP


2- in ethernetif.c:

netif->flags |= NETIF_FLAG_IGMP; //in low_level_init function


3-in my source file (for both client and server projects):

implemented the following code:


void recCallBack (void)
      printf("connected");  //BREAK_POINT
static void UDP_Multicast_init(void *arg)
   struct ip4_addr ipgroup, localIP;
   struct udp_pcb *g_udppcb;
   char msg[] = "hello";
   struct pbuf* p;
   p = pbuf_alloc(PBUF_TRANSPORT,sizeof(msg),PBUF_RAM);
   memcpy (p->payload, msg, sizeof(msg));


   IP4_ADDR(&ipgroup, 224, 0, 1, 129 ); //Multicast IP address.
   IP4_ADDR(&localIP, 192, 168, 1, 2); //Interface IP address
   #if LWIP_IGMP
      s8_t iret = igmp_joingroup((ip4_addr_t *)(&localIP),(ip4_addr_t *)(&ipgroup));
   g_udppcb =( struct udp_pcb*) udp_new();
   udp_bind(g_udppcb, &localIP, 319); //to allow receiving multicast
   udp_recv(g_udppcb, recCallBack,NULL); //recCallBack is the callback function that will be called every time you    receive multicast
   udp_sendto(g_udppcb,p,&ipgroup,319); //send a multicast packet

void telnet_shell_init(void)
   sys_thread_new("TELNET", UDP_Multicast_init, NULL, DEFAULT_THREAD_STACKSIZE, osPriorityAboveNormal);


The result: all the mentioned code steps are executed successfully in both projects (client and server) but I'm not receiving any multicast messages (or maybe not even sending)!

I added a "BREAK_POINT" in the callback function but I never reached it. Can you help me? either by suggesting a solution or at least a way to track the problem... I'm using STM32F746 Nucleo board with LWIP, FreeRTOS libraries generated by cubeMX.

Thank you.