|Subject:||Re: [lwip-users] lwip-users Digest, Vol 107, Issue 32|
|Date:||Thu, 26 Jul 2012 09:04:10 -0400|
Chen <address@hidden> wrote:
> I use lwip_send (....0), along with FreeRTOS on AVR32, to send out TCP
> Each time I call, I present 200 bytes to lwip. From Wireshark, I can
> see the packets size alternating between 200 and 1400 bytes with more
> idle time right before the 1400-byte packet
> Is there a flag I can set so that lwip sends out the packet (200
> bytes) if the output queque is empty, without trying to packaging the
> data to make it more efficient?
It is efficient as it is, as it uses less header bytes per data byte when combining multiple 200-byte-chunks into one 1400-byte-packet. Note that this is only done when there is un-ACKed data - this is the TCP representation of your "output queue is empty". Note that when using sockets, the actual output queue is always empty as tcp_output() is called after each send().
What you want is less latency, I guess (i.e. sending the packets right away without combining them)? This can be achieved by disabling the nagle algorithm, which can be done like this on most socket implementations:
int flag = 1;
ret = setsockopt( sock, IPPROTO_TCP, TCP_NODELAY, (char *)&flag, sizeof(flag) );
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