Subject: PCI network driver -- receive pkts with 0xDEADBEEF
To: None <>
From: Shashi Rao <>
List: tech-net
Date: 02/06/2001 21:29:03

i am writing a driver for a pci device that looks like a network
card. in order to test my driver, i put the device in "loopback
mode" where every transmitted packet turns around and reappears as a
received packet. i based my driver on code in the tulip and if_ti

sometimes i notice (in the rxintr handler) that the first few bytes
of the received packet are 0xDEADBEEF. these are not what i send,
and is clearly a godsend (from the netbsd kernel guys) pointing me
to a bug in either my descriptor handling or mbuf handling (some of
the buffers i handle are jumbo bufs much like in if_ti).

i've spent about a couple days trying to look for it, but still cant
find evidence of my programming the transmit descriptor wrong or
using a dmamap that is stale.

any ideas on what might be wrong? i wondered if i was using freed
mbufs (if such a thing is possible, but i couldnt find any instance
of that either)

thanks in advance
Shashi Rao