Hi all, I've recently tried sample code from chap9 Johnson and Kunze book and in DWB, the code works fine with Fast Eth ports. However, if I try to use GE ports, it only works when MTU<=192 (<=3 Mpkts per pkt). If there are >3 Mpkts/pkt, the simulation halts with error "Transmit buffer underflow". Does this mean that the code is not filling up TFIFO fast enough? Anyways, even if I set MTU<=192, I still cannot send out any traffic on real hardware (we are using ENP-2506). L3Fwdr reference design works fine on the board so I do not expect any hardware or configuration problems. Did anybody encounter this issue before? Is there any sample code (in micro C) lying around that transmits data over GE ports? Any help is appreciated. Chompi.