Re: [lwip-users] tcp_enqueue fails at more than two tcp_enqueue's

[Kieran Mansley]

On Tue, 2010-05-04 at 14:15 +0100, Jimi Simpson wrote:
> Hi Kieran,
> 
> Thank you for the response.
> 
> I have 4 threads running:

That sounds fine, and your lwipopts settings look OK too.

> Sorry for the lengthy email and lots of information, but your help is 
> greatly appreciated.

It looks from the debug output and packet capture as though lwIP is
sending some data, the other side is sending an ACK, but the stack is
not receiving or processing the ACK.  It therefore retransmits the old
packet, which the other side again ACKs, but again lwIP doesn't receive
or process the ACK and so it gets stuck in this cycle.

It would be worth turning on the LWIP_STATS code to see if there is some
resource that is running dry that would account for the dropped ACKs.
The debug log does suggest that tcp_input() is being called, but the
received packets aren't (after the first couple) recognised as
acknowledging data we have outstanding.  I would look through the code
and add more debugging to work out why these packets get ignored.

Kieran