DP83867IS: RGMII Not Detecting While Connecting XCZ7020 Based SOM

Hi Akhil, 

Could you confirm if my understanding is correct?
Working configuration:
Laptop ---- DP83867 
Not working configuration:
Laptop ---- DP83867 ---Ethernet---SOM

When the PHY is not being detected, are the LEDs blink normally?
Is this the only case the PHY becomes undetectable? Are there other link partners that cause the PHY to be not detected?
Can you also probe RBIAS and see if it gives out 1V when the PHY is not being detected and ensure that the RST_N pin is not low?

I looked at the schematic and I didn't see any noticeable things that may cause this issue. However, I doubt this is the case, but would it be possible to remove the ESD diodes and try? This is just to confirm the functionality of the MDI path without anything on it. 

Best,
J

Dear J

Please find my observations below.

1) PHY Link is getting when I connect my Laptop-RJ45-Ethernet PHY and not detecting when i connect my Laptop-RJ45-Ethernet PHY-XCZ7020 SOM

2) Reset is High when I am connecting XCZ7020 SoM.

3) I found one mistake in my design (MDIO and MDC swapped) and I corrected it in my hardware.

4) I probed the MDIO and MDC and the wave form I am getting is shared below.

5) I am using DP83867ISRGZR PHY and I am working on RGMII Configuration.

6) My address strap resistors (RXD0 and RXD2) is open (Address - 00H) so is there any possibility of address mismatch by floating pins.

I will check the RBIAS pin and get back to you.

Hi Akhil, 

If there is no MDIO connection to the laptop, the driver will not be able to detect the PHY as all communication of the PHY happens via MDIO. Is the MDIO connection to the laptop correct?

The address can be mismatched, but it shouldn't change once the PHY links up. Is the link LED blinking when the SOM is connected?

Akhil K R said:

Laptop-RJ45-Ethernet PHY-XCZ7020 SOM

How is the PHY and the SOM connected? Is it not by RJ45?

Could you provide me a block diagram of connections because I thought the SOM and the PHY are connected by RJ45. 

Best,
J

Dear J,

I’m connecting the PHY to the XCZ7020 SOM using RGMII. When I attach my laptop to the RJ45, the link LEDs blink, but I cannot ping the board.

I’ve also observed a separate — but probably related — problem with the strap-addressing: I hard-set the PHY address with strap resistors, but on power-up the address the SOM reads is different from the one I configured. This only happens when the RGMII lines are connected. If I isolate the RGMII signals from the PHY by removing the 22 Ω series resistors, the address reads correctly.

Notes:

Reset is held high after power-on (I’m not actively controlling reset).

LEDs on the RJ45 show activity when the laptop is connected, but the board never responds to pings.

The incorrect PHY address appears only when RGMII is connected; removing the series resistors makes the strap configuration behave as expected.

i have attached the complete schematics for your reference

OEPL_DCT_CR_0925_V100.pdf7181.OEPL_DCT_BCN_0925_V100.pdf

Hi Akhil, 

Akhil K R said:

I’ve also observed a separate — but probably related — problem with the strap-addressing: I hard-set the PHY address with strap resistors, but on power-up the address the SOM reads is different from the one I configured.

There is a chance that the SOM is pulling up or down on the RGMII lines causing the PHY address to be mis-strapped on the power-up. 

If you cannot ping the board, could you confirm that the SOM detects the link? If so, this may be network layer issue, not physical layer issue. Try setting network routes directly to each other so the devices can ping each other. 

Please let me know. 

Best,
J

Dear J

Thanks for your support.

I check in the Firmware side and identified pull up resistors are present in the XSA file that we are using. I will check the same by removing pull up resistor configuration in the XSA.

Hi Akhil, 

Sounds good. Please keep me updated. 

Best,
J