[lwip-users] Problem with large messages and netconn_write

[tmp]

Hi,

I’m currently running the lwIP 1.3.0 stack together with FreeRTOS on a
SAM7X controller.

I have a simple web server application up and running and I’ve also been
able to correctly obtain a “large” web page from a remote web server
(large enough to consist of several Ethernet frames).

What I haven’t been able to do is transmit large TCP packages with
netconn_write. As far as I can tell it doesn’t matter if I supply a
pointer to ROM (NETCONN_NOCOPY) or if the string is kept in RAM
(NETCONN_COPY).

The problem appears when the entire Ethernet frame going out exceeds 950
bytes (TCP package exceeds 896 bytes). The package is never received by
the computer (direct connection, using a package sniffing program to
check the traffic). netconn_write returns ERR_OK but the lwip stack
isn’t working any more (doesn’t reply to an ARP request from the
computer). 

It’s possible to send a package with netconn_write, then wait for a
second or so to make sure the package is transmitted, and then send
another package consisting of 896 byte that in turn is directly followed
by another netconn_write command.
It’s not possible to send the same thing when the second call has a size
of 897 bytes.

Is there something I’m missing here? Any ideas?

I should probably add that I’m new to lwip and the netconn interface. :)

/Andreas