Re: [lwip-users] Output fails when output size exceeds 14KB while using sockets

[Kieran Mansley]

On 17 Jan 2012, at 15:38, address@hidden wrote:

> Good evening,
> 
> Is there any reason why I need to fragment the outgoing packet myself? I
> guess it has something to do with the memory allocation but I can't put my
> finger on it.
> 
> If I set TCP_BLOCKS_SIZE in the code below to KB(14) I receive the data I
> requested on the client side, however if I set TCP_BLOCK_SIZE to KB(15) I
> won't get any of the requested data or an assertion.

It's not obvious what the problem is.  Which version of lwIP?  Does the write() 
call return an error in the case when it doesn't work?  Do you receive anything 
at the receiver?  Does anything make it on to the wire (e.g. get a packet 
capture to see).  I expect you are running out of a resource, but looking in 
your lwipopts doesn't show anything that would cause a problem at 15KB.  The 
only odd thing I noticed there is that your setting for LWIP_NUM_NETBUF depends 
on the number of connections (it is the same as the definition of 
LWIP_NUM_NETCONN) which doesn't really make sense, but the value it will be 
assigned from that definition is around 54, so should be OK for sending 15 MSS 
of data.

Kieran