[eepro100] mii-diag program - slight inaccuracy

[Donald Becker]

On Wed, 5 Jul 2000, John Cagle wrote:

> I've recently been using Donald's mii-diag program and I've come across
> something that's not quite accurate.
> 
> With my NIC & Switch combination, the BMSR register has a "1" in the bit
> position for "Link Jabber" (bmsr & 0x0002).  This causes the mii-diag
> program to print out "*** Link Jabber! ***".
> 
> However, according to the National DP83840A specification, the Link
> Jabber bit only has meaning in 10 Mb/s mode.  I'm running at 100 Mb/s,
> so this bit should be ignored.

Hmmm, curious.  I've seen false indication of link jabber at 100baseTx
before, but I don't believe that it adheres to the standard.  Does anyone
have a copy of the standard nearby to check?

I happened to have two transceiver datasheets open when this message
arrived.  Both are from the same company, Lucent.  The LU6612 doesn't
specify when the bit is valid, implying that it always is.  The LU3X31
datasheet says "During 10baseT operation..."

The minimal standard does not provide a way to tell what speed the
transceiver selects if autonegotiation fails and autosense takes over(1).  So
it's pretty much unreasonable for the bit to be set in 100baseTx mode unless
there is a data jabber(2).

(1) Many transceiver do report the speed in register 5, leaving the
    autonegotiation-complete bit unset.  A few report the speed in register 0. 

(2) Unlike 10baseT, 100baseTx is constantly sending data symbols.  But the
    transceiver does know when it's sending data vs. idle symbols.

Donald Becker				becker@scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Beowulf Clusters / Linux Installations
Annapolis MD 21403