Re: 3com 3c905C-TX driver bug: incorrect FLOW Control, speed using MII..

On Wed, 18 Feb 2004, Will Richmond wrote:

> WILL: Don, thanks for reply, my comments are also embedded:
> 
> >> We are experiencing what appears to be a bug in the 3com 
> >> 3c905C-TX drivers for redhat linux enterprise version 7.X. 
> >> Our Cisco...
> >
> >When I read Cisco, I think duplex mismatch
> >Read
> >   http://www.cisco.com/warp/public/473/46.html
> 
> WILL: we try to stick to row four (4) of the "Cisco Valid 
> Configuration Table", which is GOOD, according to cisco--
> normally.

Note that the table is labeled "Auto-Negotiation Valid Configuration".
Line 4 *not* using autonegotiation: manually configuring full duplex
disables auto-negotiation.

This is not a standard-conforming (read that as "violates the Ethernet
standard").

If you fear autonegotiation, disable it, force the speed  and set half
duplex.  The NIC will sense the speed and use standard Ethernet CSMA/CD
("half duplex").  Keep in mind that for a workstation there is only a
very slight speed advantage for full duplex. Compare that to the pain
and grief caused by forced full duplex.

> >> ...and 3com switches are hardset for 100 FD, no flow 
> >> control in either direction.
> >
> >Accckkkk!!!  Don't do that.  Read the URL above.  That's 
> Cisco saying "Uhmmm, yeah, that thing we told you to do, 
> uhmm, ignore that."
> 
> WILL: I scanned link and couldn't figure out what part about 
> cisco's suggestion was retracted: flow control, or 
> hardsetting? Hardset to autonegotiate change is not an option 
> as many things fail when both ends are set to auto-neg. Flow 
> control can be turned on, but I normally leave off.

What fails?  The only case where autonegotiation fails with a few broken
older Cisco (and 3Com) switches.  It appears that Cisco implemented
autonegotation in firmware, without understanding that the timing
requirements couldn't be met when the switch was busy.

-- 
Donald Becker				[email protected]
Scyld Computing Corporation		http://www.scyld.com
914 Bay Ridge Road, Suite 220		Scyld Beowulf cluster systems
Annapolis MD 21403			410-990-9993

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