I managed to get a pair of Tulips going between a NetBSD system and 
a DUnix system.  (Both Miatas.)  The trick is/was to set the mode 
manually at the console (>>> set ewa1_mode Fast).  It works fine 
in half-duplex.  It hangs or crawls if you hit it hard in full duplex.  
(FTPing a 100K byte file is enough to provoke the problem.) 

At one point, I noticed the LEDs on the cards blinking.  I assume 
the autonegotation heuristics are incompatible and they were dancing 
around in circles. 

Intel 82588s seem to work OK between NetBSD and DUnix systems.  They 
agree on full-duplex and it works. 

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I learned some more about the printout from ifconfig.  The "SIMPLEX" 
on the first line doesn't mean half duplex.  It means the hardware 
won't hear any packets it sends. 

fxp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        address: 00:08:c7:08:2a:59
        media: Ethernet autoselect (100baseTX full-duplex)
        status: active
        inet 10.0.3.83 netmask 0xffffff00 broadcast 10.0.3.255

The full/half indication is on the media line.  (But the "half" won't 
get printed.) 


From /usr/include/net/if.h

#define IFF_SIMPLEX     0x800           /* can't hear own transmissions */