Re: [lwip-users] tcp_write() errors on snd_queuelen

[Simon Goldschmidt]

Tim Lambrix <address@hidden> wrote:
> > Can you include your lwipopts.h in this post?
> 
> Should be attached.  I could use some help verifying I have it configured
> correctly for my application with respect to the memory requirements at
> some point too.

I can comment on generic lwIP options (without knowing your platform in detail):

>>>>> snip >>>>>
#define TCP_WND                         2048          // default is 2048
#define TCP_MSS                         1050          // default is 128
#define TCP_SND_BUF                     (8 * TCP_MSS) // default is 256, was 6 *
#define TCP_SND_QUEUELEN                128//(4 * (TCP_SND_BUF/TCP_MSS))
<<<<< snap <<<<<

In general, you might run into receive problems with the TCP window being so 
small compared to the MSS (TCP_WND is only used as receive window, the transmit 
window is taken from the remote host's SYN packet). It should be at least 2*MSS 
but is encouraged to be at least 4*MSS if your memory constraints allow you to. 
This is to make sure the TCP sliding window algorithm can work correctly.

TCP_SND_BUF and TCP_SND_QUEUELEN seem OK. Those settings allow you to make 64 
or 128 calls to tcp_write() (one pbuf per call when copying data, 2 per call 
when not copying) and to enqueue 8400 bytes of data in these pbufs.

The other memory settings seem OK, too. However, that depends on the number of 
parallel connections.

Simon
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