Freertos_connect always timesout

frankthetank34 wrote on Friday, May 06, 2016:


I have ported over the tcp stack to the tiva tm4c1294 launchpad. I am playing with socket connections.

I successfully get assigned a ip address via dhcp. Using wireshark, I also see my device periodically sending out a Gradtuitous ARP for (my ip address). Makes me believe my device is talking. However, when I setup a socket, I can never get it to successfully connect. The value returned is a 116, or pdFREERTOS_ERRNO_ETIMEDOUT.

Any suggestions as to where to go from here?


rtel wrote on Saturday, May 07, 2016:

What are you trying to connect to? Do you have an external echo server set up, or something similar? If so, could you please post a wireshark log of the attempted communication.

Some links that may be helpful, although I expect you have seen them already: (this one is referring to an example that is in the download).

heinbali01 wrote on Sunday, May 08, 2016:

Yes a WireShark PCAP file would be useful in this case :slight_smile:

Suppose that you want your device to connect to your laptop, for example IP address, port 7.

You can connect to other laptops or devices, but then WireShark may not be able see all traffic.

Make sure that you assign this port 7 in network byte order:

	addr.sin_port = FreeRTOS_htons( 7 );

otherwise +TCP will try to connect to port 0x0700 in stead of 0x0007.

A FreeRTOS_connect() will do the following:

  • It will start an ARP lookup request for
  • It waits for a reply to this ARP request
  • It will send out a TCP SYN packet

All three actions should be visible in WireShark.

In case you connect to an outside IP address, the hw address of a router (gateway) will be lookup up.


heinbali01 wrote on Sunday, May 08, 2016:

Ps. The target IP address can be asigned safely in this way:

	addr.sin_addr = FreeRTOS_inet_addr_quick( 192, 168, 2, 100 );

Both FreeRTOS_inet_addr_quick() and FreeRTOS_inet_ntoa() work with IP adddresses in network-byte order (i.e. big endian)

frankthetank34 wrote on Wednesday, May 11, 2016:

Hi Hein,

Your questions and suggestions really helped. I had been using wireshark, but one of the things that confused me was I would only see my dhcp messages go out. Then silence from my device. I am on a switched network. I may be a network newbie but I should have known switches mask messages to network plugs/ports that don’t have the inteneded device connected to it.

Once I got around the wireshark issue, I had another light bulb moment. I asked our IT folks to set me up with a connection not behind our network firewall. Turns out that didn’t happen. We love to lock things down. Reason I was failing connection was our firewall. I am up an running now, no issues. I was convinced it was my code. I need to learn to trust myself more.