DP83869HM: Packets Missing During Ping

Hi Srinadh,

The only thing standing out in the schematic are these terminations on the MDI lines. If you remove these terminations, do you notice any improvement?

Furthermore, have you performed any loopback testing on the design? Loopback testing is the best way to narrow down where the issue is occurring. A ping test will utilize the entire signal path: MAC <--> PHY <--> Cable <--> PHY <--> MAC, so it is difficult to say where the breakdown is happening from a ping test alone.

• I recommend following the steps in section 2.5.2 of our DP83869 troubleshooting guide to perform MII loopback. MII loopback is enabled on DP83869 by setting register 0x0000[14]

Best,

Shane

Hi Hauser,

In one of the previous designs, the termination resistors were already placed, and I believe there should not be any difference. However, I will verify this by removing the resistors and testing again.

Yes, we have performed loopback testing. What we observed is that the request is being sent from the client (laptop) to the server (our custom board), but sometimes the request is not transmitted successfully. Does this mean the server is unable to receive the request, or that the client is occasionally unable to send it? Please suggest what might be causing this issue.

Hi Srinadh,

Srinadh Moka said:

the request is being sent from the client (laptop) to the server (our custom board), but sometimes the request is not transmitted successfully

This suggests there is some breakdown in communication on the transmit path, however we should narrow down whether the issue is on the MII or MDI side of the DP83869. I assume the DP83869 sits on the laptop/client port in your description. In your MII loopback testing, were you able to receive error-free data on the laptop back from the PHY?

• If the laptop MAC can send data and receive it back error free while the DP83869 is in MII loopback, the RGMII communication is working. For reference this is the path that MII loopback will test:

If the MII loopback testing works without errors, the problem should be somewhere on the MDI. The MDI connection consists of the following

• The PCB trace between the DP83869 and the RJ-45 port: Perform reverse loopback
• The cable used: Test multiple cables to see if this affects the packet loss.
• The Link Partner: Test multiple link partners to ensure the issue is not following one link partner.

Best,

Shane