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DP83848K: Longer link time than expected

Hiromu Susami
Prodigy 400 points
Part Number: DP83848K

Tool/software:

Hi exparts,

I have qustion about DP83848K link time. This is my first support for ethernet phy, so I hope your kindly support. If I need more information, please tell me.

Customer situation:

Two DP83848Ks are mounted on a single circuit pack. Two DP83848Ks were folded and connected for shipment testing. It took more than 30 seconds to establish the link. They want to know the cause.
*Two DP83848Ks are unreset at the same time.
*Two DP83848Ks are connected to each other with a straight-through cable. (TX-to-RX, RX-to-RX).

Q1. In the above configuration, each DP83848K will run Auto MDIX at the same time. Is it possible that by repeating TX and RX to each other, it will not be possible to connect or it will take a long time to connect?

Q2. Are there any reports or errata that this or other device is experiencing any of the above? 

(This is an example of a device from another company, and there was errata information about the issue of not being able to connect and the connection taking a long time due to Auto-MDIX)

https://www.analog.com/media/en/technical-documentation/data-sheets/ADIN1200-silicon-anomaly.pdf

Q3. If Auto-MDIX cannot be connected to each other continuously, is it possible to grasp the situation by measuring the communication waveform, accessing registers, etc.?

Thank you for your support.

Regards,

Hiromu

  • 0
    TI__Mastermind 19621 points

    Hi Hiromu,

    Thank you for submitting your query. Would it be possible to connect each 848 to a different link partner, instead of to each other, and see if that also take a long time to link up?

    We can also rule out the Auto-MDIX doubt by disabling it in Reg 0x19 and forcing MDI.

    Regards,

    Alvaro

  • 0 in reply to Alvaro (Al-vuh-roe) Reyes
    TI__Prodigy 400 points

    Hi Alvaro,

    Thank you for your comment. I will ask the customer for the behavior if he connect each 848 to a different link partner.

    My question is, "Is it possible that by repeating TX and RX to each other, it will not be possible to connect or it will take a long time to connect?" Do you have any answers on this? 

  • 0 in reply to Hiromu Susami
    TI__Mastermind 19621 points

    Hi Hiromu, 

    It shouldn't have an effect, but to rule out doubt I suggested disabling Auto-MDIX. We can try disabling Auto-MDIX on one of the DP83848s and leave it enabled on the other. This will keep one of the 848s in a fixed MDI state and the other should be able to use the Auto-MDIX feature to correctly link up.

    Regards,

    Alvaro

  • 0 in reply to Alvaro (Al-vuh-roe) Reyes
    TI__Prodigy 400 points

    Hi Alvaro,

    ・When connected to different link partners, the link takes approximately three seconds.

    We are checking if you can change register Reg 0x19. It's going to take a while, so I'd like to check it out first:
    ・ If the problem of longer link time is caused by the operation of Auto-MDIX, or if it is not, is there a solution for each problem?

    ・As I asked in Q3, is it possible to grasp the situation by measuring communication waveforms, accessing registers, etc.?

  • 0 in reply to Hiromu Susami
    TI__Mastermind 19621 points

    Hi Hiromu,

    So when the two 848's are connected to each other, it takes ~30 seconds to link up, but when connected to a different link partner it took ~ 3 seconds?

    Accessing Registers would be the first place I would check. If register access is available, could you read register 0x00 - 0x1F for the following conditions:

    1. Baseline - Ethernet cable is disconnected
    2. 848 linked up with 848
      1. Provide register dump for both 848 PHYs
      2. If possible, provide a register dump during the ~30second link up period
    3. 848 linked up with different link partner

    Regards,

    Alvaro