Re: [lwip-users] curious large packets and transmit stuck

[Kieran Mansley]

On Mon, 2007-01-29 at 20:06 +0100, Andre Puschmann wrote:
> hello guys,
> i did a port of lwip to our custom mpc5200 board.
> transmission runs quite fast so far, but i still have stability problems.
> i am not sure if this is a lwip related problem or if it comes from
> lower levels, e.g. fec driver, interrupt handling or even dma problems.
> 
> with my lwip app i constantly transmit 1000Byte long packets. this
> works quite well up to a certain point. sometimes i even transmit 3GB of
> data until it starts to stuck, but sometimes it hangs after 10MB.

At what level are you transmitting these packets?  Is it an application
doing 1000 byte writes to the network, or do you have something low
level that is output the packets directly?

> in my ethernet transmit function i did some sanity checks, doing so
> showed up that lwip sometimes tries to transmit packets larger than
> 1300Byte which shouldn't be the case.

If an application does 1000 byte writes, lwIP (or any other TCP stack)
can decide to split them or combine them as it wishes to form packets up
to the MTU of the network.  At the application level there is no concept
of packets: it is just one single stream of bytes.  The splitting into
packets is done by the stack, and it can choose where it does these
splits, and so the lengths of the packets.  

Hope that helps, but it doesn't sound like the large packets are the
cause of your problems.

Kieran