[lwip-users] raw interface, detecting retries

[lwip]

Moin all,

I use the raw interface to xmit some lengthy data over TCP. My applications 
works fine so far.

I have difficulties to implement retries in case of lost datagrams.

tcp_write sends data without copying it. The data is kept until tcp_sent callback notes success. Thereafter more data is prepared 
and xmitted.

What happens if the data gets lost? I expect tcp_sent will not be called as the other side did not acked it. After a while the 
tcp_poll callback will be called, which in turn could retransmit the data.

Nevertheless I see tcp_poll callback even when everything works fine.

How can I differentiate whether a retransmit is required or more data should be 
send?

Did I miss something in the docs? Any help apreciated.

Friedrich