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DP83867E: Slow with 100Mbps switch , fast with gigabit switch

ruchi shah
Prodigy 30 points
Part Number: DP83867E

I am using DP83867E , when connected to a gigabit switch the speed seems fine.

But when same is connected to a 100 Mbps switch , it slows down drastically . One ping cmd takes around 400 ms.

Is there any specific settings that need to be taken care in its linux device tree config ?

Is it related to rx, tx internal delays?

Or the issue can be in hardware designing?

What are appropriate steps to debug the issue?

Thanks.

  • 0
    TI__Mastermind 18425 points
    Hi Ruchi,

    Ping is a higher level protocol. In general the PHY lantecy will increase in 100M mode but the increase is in the order of ns. The ms difference that you are observing can be a result of how ping is handled within the MAC at different speeds. From a PHY perspective, a ping packet is not different than a normal data packet. The PHY will transmit and receive them the same.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 30 points

    Thanks for the reply.

    I have 2 more concerns.

    1> Are there any specific changes that need to be done in the linux device tree for DP83867 apart from standard once given in documentation?

    2> Will the capacitance values used at power supply pins of PHY, affect its speed of operation with 100 Mbps switches?

  • 0 in reply to ruchi shah
    TI__Mastermind 18425 points
    Hi Ruchi,

    There is a related E2E post on DP83867 Linux Device Tree config: e2e.ti.com/.../563409

    As far as power supply caps are concerned, they will not affect the speed of operation or the PHY's performance with 100Mbps switches.

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 30 points

    Ok, Thanks.

    If you can suggest  what troubleshooting steps we need to follow, thereby we can conclude whether its a software issue or schematic design issue?

  • 0 in reply to ruchi shah
    TI__Mastermind 18425 points
    Hi Ruchi,

    The PHY supports loopback modes on both MAC side and cable side. Using the MAC side loopback you can transmit data from host MAC to DP83867 and DP83867 will loop it back to MAC. In Cable side loopback, DP83867 will send all receiving data on the cable back to the link partner. These modes will enable you to verify that communication between MAC-PHY and PHY-Link partner is error free. This will help you check that the hardware design is operating correctly. For MAC side loopback you can use Digital or Analog Loopback, for cable side loopback you can use Reverse Loopback. These are described in the datasheet.

    -Regards,
    Aniruddha