Electronic – How MDIO , SGMII is connected with phy chip and ethernet controller

From the datasheet

• Fully Compatible with 10/100/1000Base-T Networks
• Integrated MAC and 10Base-T PHY
• Supports One 10Base-T Port with Automatic Polarity Detection and Correction
• Supports Full and Half-Duplex modes

So, it is 10mbps FD (and yes, 10baseT supports full duplex, at least some cards do) and, as all 10baseT devices is compatible with newer networks.

I resolved the problem, but it took re-manufacturing the board. The problem seemed to be with the routing and layer stack-up. The USB and Ethernet traces did not have correct impedance due to two reasons.

Firstly, the track geometry was not correct for 90 ohm (USB) and 100 ohm (ETHERNET) differential impedance. If your layout software does not support differential routing (eg: Altium does), then you will need to use something like SaturnPCB to calculate the track geometry and manually route the traces accordingly (I had to do this).

Secondly, and most importantly, the layer stackup was not correct to support USB and Ethernet high speed traces.The stack-up was TOP-INNER SIG-GND-BOTTOM and the high speed traces where routed on top layer. USB and ETH traces require a solid ground plane underneath and since this was not the case on my board it really messed up the signal integrity. Putting a solid ground plane (hence changing the stack-up to TOP-GND-INNER SIGNAL-BOTTOM) fixed the signal integrity issues.

I also cleaned up the placement of decoupling caps around the LAN9512 IC.

After these changes, the new board worked without problems. If you're using the raspberryPi to clock the LAN9512 (as B+ with LAN9514 does), then you also need to configure the Pi to output a clock signal. You can find info on this here: http://www.elektricks.net/raspberry-pi-compute-module-general-purpose-clock/ If you have a separate oscillator for the LAN9512 then ignore this paragraph.

Hope that helps!