[lwip-users] Re: Assertion : "tcp_enqueue: no pbufs on queue => both queues empty"

[Kelvin Lawson]

> I use lwip in a embedded system, one time I have got this the following message:
> "tcp_enqueue: no pbufs on queue => both queues empty"
> Exactly on this line:
> LWIP_ASSERT("tcp_enqueue: no pbufs on queue => both queues empty",
>       pcb->unacked == NULL && pcb->unsent == NULL);

I had this problem recently, and it was down to my setting for 
TCP_SND_QUEUELEN. This must be less than 256, because the data type used 
for storing the queue length (snd_queuelen) is 8 bits. Any larger and 
the snd_queuelen counter will overflow.

Hope this helps,
Kelvin.