Re: [lwip-users] tcp_write problem after the first transmission

[address@hidden]

As a side note, I hope you are calling the loop below in the 
tcpip_thread, not from another application thread, which would violate 
lwIP threading.

Aside from that, what Bernhard said is true: the packets are buffer for 
retransmission until they are ACKed by the remote side, which cannot 
happen while you are in the loop. As a result, you either have to bufer 
your data somewhere else and call tcp_write() from the 'poll' or 'sent' 
callback - or increase TCP_SND_QUEUELEN to 20 (in your case, depends on 
your application) to be able to internally queue as much data as you 
have to at maximum.

Simon


Daniel Berenguer wrote:
> I'm trying to send a bunch of TCP packets using the raw API but
> tcp_write is returning -1 (out of memory) after the 8th packet.
>
> for (i=0 ; i<20 ; i++)
> {
>      strcpy(buffer, "holaaa");
>      res = tcp_write(pcb, buffer, 7, 0);
>      tcp_output(pcb);
> }
>
> I've used many variants of the above code (with delays, w/o
> tcp_output, ...) but the problem is always there. The first packet is
> sent immediately after the first tcp_write but then, tcp_write just
> pushes the packets into the sending queue. TCP_SND_QUEUELEN is set to
> 8 so once the TX queue gets overflowed tcp_write starts returning -1
> and the contents of the queue is finally sent (only 7 packets of 20
> though).
>
> Any idea?
>
> Thanks.
>
>
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