L4 ethernet driver and stack setup

Hi all, I've "extracted" the E1000 driver code from the TFTP server to get some packet data directly into L4. I've noticed that if I load this task with the loader then the TX part sends garbage. I then added (for fun) the attribute (section "STACK") to the buffer from which the packet is send and now it works. Can anybody explain this to me! Send a link to some use full doc? Thanks Leon