Subject: Re: de0: abnormal interrupt: transmit underflow (fwd)
To: fission <>
From: Manuel Bouyer <>
List: tech-net
Date: 01/12/2000 21:19:37
On Tue, Jan 11, 2000 at 06:30:27PM -0600, fission wrote:
> I am forwarding this message along because I did not get any replies for
> this on the port-macppc list.  Please cc: any replies to me as I am not on
> tech-net.
> What exactly is a transmit underflow anyways?

The ethernet chip starts tranfering the packet before it has read it all in
its own buffer (to reduce round-trip time), but if the PCI bus can keep
with the speed (this can occur if a higth-priority device grabs the bus for
example) the tranmitter runs out of data. That's it.

I get the same on my PC with de boards, but it usually bup the threshold for
each underflow, eventually ending in store-and-forward mode (in which case
underflows are not possible any more).

Manuel Bouyer <>