Re: [lwip-users] Problem doing UDP multicast receive using netconn API

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Do you have NETIF_FLAG_IGMP set in your netif's flags?

Honestly, I haven't used IGMP so far, but looking at the code of igmp_joingroup(), which is called by netconn_join_leave_group, ERR_VAL is the default return value, which means that your netif isn't correctly detected (either it does not have NETIF_FLAG_IGMP set in its netif->flags or the IP address is wrong, which can't be the problem from reading your code).

Simon


David K Squires wrote:

Dear Group Members,

 

I am struggling to try to receive UDP multicast messages with the Atmel UC3A lwip 1.3.2 port.

 

I have been successfully sending UDP multicast packets with lwip for a couple of years using the netconn API. But now I need to receive them in a different FreeRTOS task.

 

Here are the particulars:               Multicast Group Address = 224.0.0.0, destination UDP port = 55555

 

I've enabled the IGMP code in lwip and everything builds fine. I have coded up several attempts to set up to receive UDP multicast packets for the above group and port as follows:

 

=============================== Code snippet ================================================

(other includes here)

 

/* lwIP includes. */

#include "lwip/api.h"

#include "lwip/memp.h"

#include "lwip/inet.h"

#include "lwip/ip_addr.h"

#include "lwip/udp.h"

 

(other includes here)

 

my_task_function()

{

   struct ip_addr s_mcast_ip_addr;           // MCAST IP Address

   struct netconn *conn;

   int lwip_status;

   err_t err;

 

   /* Multicast Group IP address bytes are specified in MS to LS order here */

   /* The group address is 224.0.0.0 */

   IP4_ADDR(&s_mcast_ip_addr,(NetConfig_s.udp_mcast_group_addr.addr >> 24) & 0xff,

                                                    (NetConfig_s.udp_mcast_group_addr.addr >> 16) & 0xff,

                                                    (NetConfig_s.udp_mcast_group_addr.addr >>  8) & 0xff,

                                                    (NetConfig_s.udp_mcast_group_addr.addr & 0xff));

               

    // Create a new UDP connection

   conn = netconn_new(NETCONN_UDP);

 

   // Note: the above call returns a valid pointer (non-zero)

               

    // Bind to the multicast group address 224.0.0.0 and UDP port 55555  (is this call needed??)

    // lwip_status = netconn_bind(conn, &s_mcast_ip_addr, NetConfig_s.udp_dest_port);

               

   // Allow packets from ANY remote host on any port. Is this call needed?????

   // I suspect this call is not needed for UDP

   // netconn_connect(conn, &s_remote_ip_addr, 0);                      //  what do we use for "Any UDP Port?"

               

   err = netconn_join_leave_group (conn,                                             // netconn *

                                                          &s_mcast_ip_addr,                              // Multicast Group Address (32-bits: 224.0.0.0)

                                                          &NetConfig_s.ip_addr,       // Local interface IP address = 192.168.1.21

                                                          NETCONN_JOIN);                  // We want to join this multicast group

 

=============================================================================================

The code from which this snippet was taken compiles fine with no errors or warnings.

 

The problem seems to be in the netconn_join_leave_group function call. It returns err = -9 (ERR_VAL).

 

The first parameter, conn, is non-zero, indicating a reasonable, initialized struct netconn  pointer.

 

The second parameter has been checked and really is 224.0.0.0.

 

The third parameter is a pointer to struct ip_addr which is initialized with the IP address of our local Ethernet interface.

 

As you can see, I've commented out calls to the netconn_bind and netconn_connect functions; it's not clear whether or not these are necessary.

 

Examples of using this function seem to be non-existent, hence my decision to post  a humble cry for help on the lwip forum.

 

Incidentally, I've patched the Atmel UC3A MACB driver to allow all broadcast and multicast packets to be passed to lwip. However, I am not yet to the point where this matters, given the above error scenario.

 

Any help would be greatly appreciated.

 

Thanks,

 

Dave Squires

 

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phone:  (321) 242-8611

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