I'm trying to get a 100Mbit connection with
a DE500 ethernet card. (NetBSD-current/i386)

The card is recognized correctly:
> de0 at pci0 dev 13 function 0 at irq 10
> de0: DE500-XA 21140 [10-100Mb/s] pass 1.2
> de0: address 00:00:f8:30:94:ca

It works with 10Mbit, and it used to work under
NetBSD-1.2 with 100Mbit too.
Not it looks the following:
If I do a "ifconfig de0 link2", it doesn't cause any
effect. "ifconfig de0 -link2" prints
"de0: enabling 10baseT port".

I observed that the TULIP_ALTPHYS flag in
sc->tulip_flags is set all the time.
So I set it to 0 by the debugger. After that,
the "ifconfig de0 link2" switched the card to
100Mbit (but without the console printout), the link got
up, but after a second or so, "de0: enabling 10baseT port"
appeared and the card switched back.

There seems to be a bug in the driver logic. Unfortunately,
the tulip driver is rather complex and it would take a while
to understand its working.
What do the experts say?

best regards
Matthias Drochner