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RM48 LWIP Demo does not send ARP request

Martin Beakes
Intellectual 325 points

Hi, 

I'm currently writing a test software based on LWIP demo provided by TI with RM48 processor..  

I created a small demo echo server that works fine. The echo server wait's for a packet, modify the packet and send it back. This works fine. 

Now at the beginning of the code, I added a code to transmit UDP packet. 

Issue : 

The UDP packet are not sent out until the board receives a ARP request from my computer.  As soon as the ARP request are received, the UDP packet that was queued are sent out.  

This problem can be observe when you power on the board and and the application tries to send UDP packet. As soon as the another device tries to communicate with the board, the other device send a ARP request and then the board send the UDP packet. 

Is there something that I should setup/configure in the stack to have lwip to send ARP request ? 

  • 0
    Intellectual 325 points
    Here is an update:

    in lwipopts.h, I did the following:
    #define STATIC_IP_ADDRESS 0xC0A80702 (Initially set to 0, I changed it since I'm using static IP address).
    #define LWIP_ARP 1
    #define LWIP_DHCP 0

    Now when debugging the code, I can see that the stack sends 2 ARP request, the first one for 192.168.7.2 and then the one that correspond the to IP address of my computer (192.168.7.10). So it works .

    However, if load the code in the processor and perform a power cycle, I got the same issue as previously. No ARP request are sent. If I ping 192.168.7.2 then Lwip sends the packet.
  • 0 in reply to Martin Beakes
    TI__Guru**** 190616 points
    Hi Martin,
    Unfortunately we have no expertise in LwIP. For LwIP related questions I think you will find better support at the LwIP forum. http://savannah.nongnu.org/

    What might have happened is that the outgoing UDP packet is automatically preceded with an ARP-request to discover the targeted MAC address. The ARP packet generated in this case is invalid, so it is never answered and the UDP-packet is not sent until the ARP table is updated.

    Have you tried the DHCP instead of the static address? Will it make a difference? Again we have limited knowledge on the LwIP.
  • 0 in reply to Charles Tsai
    Intellectual 325 points
    Hi,

    In my case, in debug mode, when Lwip stack sends the ARP packet, it is a valid packet and the Computer replies and the UPD packet is sent.
    I did not tried DHCP mode since I do not have DHCP server on that subnet.

    Thanks. I will look on the website that you proposed.