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Date: Sun, 30 Jun 2019 09:27:14 +1200
From: "Lilith Bryant (dark141 AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Subject: Re: [geda-user] Ethernet PHY KSZ8081 auto negotiation link up
 problem
To: geda-user AT delorie DOT com
In-Reply-To: <20190629203837.ec779cc02f9ac3f1da0cc593@gmail.com> (from
 geda-user AT delorie DOT com on Sun Jun 30 06:38:37 2019)
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FWIW, I use this chip in a client's design, and they do talk to each other 
fine in this design.

Though I have had issues with them being extremely touchy w.r.t. the output 
impedance of the CPU lines feeding the RMII signals, typically though this
results in just lots of CRC errors, rather than AN failing.   Where as the
obselete KSZ8031 was much more tolerant of wrong impedences.

I'd probably first look that the control regs are indeed being set correctly, i.e.
read them back to verify,  maybe the MDIO bus isn't working right.  I can't
remember if AN is on by default with these chips.

I'd also look at clock quality.  Maybe you've got as much jitter, such that 
if BOTH ends are jittery then AN doesn't work, but if only ONE end is jittery,
then things work well enough.

On 2019-06-30 06:38:37, Nicklas SB Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via geda-user AT delorie DOT com] wrote:
> I have an Ethercat card there I choosed KSZ8081 as PHY, driver for Ethernet,
> datasheet where registers where not available for chip used in reference
> design BCM4251XA1KMLG and KSZ8081 is common so I expected it work.
> 
> Auto negotiation works with other devices ordinary computer, switch, other
> ethercat card but not other cards with the same PHY KSZ8081. I could
> actually put ethercat cards with KSZ8081 closest to computer another
> ethercat card in between an ethercat card with KSZ8081 at the then and work
> counter say it is communication in between all three cards in the chain.
> Problem is bound to auto negotiation and there should be no other
> communication before link up so I expect same problem will if it used for
> ordinary ethernet.
> 
> Registers suggest auto negotiation work, ack is sent but link up never
> occur. Do anybody have any idea?
> 
> 
> Regards Nicklas Karlsson
>