Duplex operation of BayNetworks FA310tx cards

[Donald Becker]

On Fri, 11 Sep 1998, Simeon Warner wrote:

> I have a bunch (14) dual PII 300 PCs dedicated to physics calcs 
> (not really beowulf since we aren't using them in parallel right
> now) with FA310tx cards. I setup linux on them identically 
> (using RedHat's kiskstart mechanism) and notice that the cards
> on some machines have the duplex light lit and others don't.
> They are all plugged into the same switch (Cisco2900xl).
> I haven't done speed tests to see what they are actually doing 
> except ftp to verify I get more than 10Mb/s so they must be running at
> 100Mb/s as indicated by the lights.

I don't know about that specific model, but Cisco switches are known to have
problems with autonegotiation.  Cisco resisted implementing it for years,
and then implemented it incorrectly on some models.  For this reason Cisco's
documentation suggests that you force the duplex.

I recommend that you do *not* force full duplex, unless
  You have a non-MII 21140 card that cannot autonegotiate (older designs) or
  You must connect to old equipment that does not autonegotiate.
When you do force the duplex, make certain that the machine is never moved
to repeater, because that resulting out-of-window collisions will usually
stop the transmitters on most attached machines.

Forcing full-duplex also means that the LEDs might not light correctly.
When a FD LED is attached to MII transceiver, it typically only turns on
when full-duplex is negotiated or when a transceiver-specific register is
written.  Since the Tulip driver avoids transceiver-specific code (except to
work-around broken Level-One transceivers, grrr..) it sometimes cannot turn
on the FD LED.

Complicating this is that there are at least two options for forcing full
duplex: advertising/accepting only FD entries (10-FD and 100-FD), or turning
autonegotiation off completely.  These two options may result in different
FD LED behaviors, with neither one being obviously better.

When the FD LED is attached to the general purpose pins it will only be lit
if you select the specific media table entry e.g. 10baseT-FD and that media
table entry is written correctly for the board.  It will not be turned on if
you just force full duplex and let the driver autosense the speed, if the
media table is the generic Digital example, or if it's a MII transceiver
(there is no media table entry for setting the general purpose pins for MII
media).

Anyway, the bottom line is that there are many cases where the FD LED does
not work with a non-card-specific 21*4* driver.  However all cards of a
single design should behave similarly.

Donald Becker					  becker@cesdis.gsfc.nasa.gov
USRA-CESDIS, Center of Excellence in Space Data and Information Sciences.
Code 930.5, Goddard Space Flight Center,  Greenbelt, MD.  20771
301-286-0882	     http://cesdis.gsfc.nasa.gov/people/becker/whoiam.html