EthernetInterface Lib : only 3 sockets ?

11 Nov 2013

Hi there,

my application needs at least 3 UDP sockets and I'm having trouble with it, I cannot create more than 3 sockets. I also found a post in the questions section, where someone reports the same with 3 TCP connections.

I made a small test program that attempts to start a thread, and inside the thread I call lwip_socket(AF_INET, SOCK_DGRAM, 0) - it works for 3 sockets, then fails.

After digging into the depths of the lwip things, I think the function tcpip_apimsg() fails, when it calls sys_mbox_valid(&mbox). I do not yet understand what this code does, "mbox" is a static variable, so why would the code work 3 times and then fails.

Can anyone confirm this behaviour ? Or is there anyone with more than 3 sockets ?

sample code

#include "mbed.h"
#include "EthernetInterface.h"

Serial pc (USBTX,USBRX);

void SocketThread(void const* args)
   int aSocket;
   aSocket = lwip_socket(AF_INET, SOCK_DGRAM, IPPROTO_UDPLITE);
   if (aSocket < 0)
   while (true) osDelay(1001);

osThreadDef(SocketThread, osPriorityNormal, 512 );

static EthernetInterface interface;

int main()
   pc.printf("\r\nHello netTest \r\n");
   interface.init("", "", "");

   osThreadId tid[16];
   for (int i=0; i<8; i++)
      tid[i] = osThreadCreate(osThread(SocketThread), (void*) i);
      if (tid[i] == NULL) pc.printf("Failed to create a thread #%d \r\n", i);
   pc.printf("\r\ndone \r\n");
   while (true) wait(1.0);

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