[lwip-users] A new users request for help with sending TCP Packets on Demand

[Mitch Jones]

Hi there lwip users, I've had success sending UDP packets on demand, but am not finding success doing the same with a TCP Connection.

For now I'm just implementing a base case inside a function that I call after lwip_init to try to get it working. What I'm wanting in the end is to have a function I can call with an IP and data to send to it. Here's what I've got now.

void echo_tx_tcp()

{

  volatile int dumb = 0;

  err_t wr_err = ERR_OK;

  struct tcp_pcb *l_tcp_pcb;

  l_tcp_pcb = tcp_new();

  ip_addr_t dest_ip =

  { ((u32_t)0x0C0C0C2BUL) };

  wr_err = tcp_bind(l_tcp_pcb, &dest_ip, 12);

  if (wr_err == ERR_OK)

  {

    dumb +=1;

  }

  wr_err = tcp_connect(l_tcp_pcb, &dest_ip, 12, echo_accept);

  if (wr_err == ERR_OK)

  {

    dumb +=1;

  }

  tcp_sent(l_tcp_pcb, echo_sent);

  struct pbuf *pl = pbuf_alloc(PBUF_TRANSPORT, 1024, PBUF_RAM);

  unsigned char buffer_send[1024] = "My Name Is Mitch TCP";

  pl->payload = buffer_send;

  pl->len = 1024;

  pl->tot_len = 1024;

  wr_err = tcp_write(l_tcp_pcb, pl->payload, pl->len, 1);

  if (wr_err == ERR_OK)

  {

    dumb +=1;

  }

  wr_err = tcp_output(l_tcp_pcb);

  if (wr_err == ERR_OK)

  {

    dumb +=1;

  }

  return;

}

The "dumb" variable is just to force the compiler to not skip the wr_err assignement, which I'm monitoring using a debugger. What I've found is that wr_err is ERR_OK up until the tcp_write command after which it is -1 (ERR_MEM). I'm using a NXP processor and their canned demo, I do not see a buffer length function in there. Nonetheless, that is where I stand, and I'm in need of some advice as to what might be wrong.

Regards,

Mitch Jones