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DP83822IF: The device cannot build up link once auto-negotiate function is disabled

John11513
Expert 5500 points
Part Number: DP83822IF

Hi Experts,


My customer reported an issue of DP83822IF. 

Normally the device can work properly if one equipment with DP83822IF is connected to another same equipment or a PC, if both sides is enabled with Auto-Negotiation. However, the problem is the equipment cannot build up 100BASE-TX link once one of side is disabled for Auto-Negotiation. Customer has tried enabling Auto MDIX, however cannot fix the problem.

How should we solve the problem?

Thank you!
John

  • +1
    TI__Mastermind 32485 points

    Hi John,

    When a 10/100 PHY is set to disable auto-negotiation, its MDI is flooded with scrambled idle signals as opposed to FLP (fast link pulses) which come with auto-negotiation. As the other side is expecting FLPs but instead getting idles, the PHY cannot go through the required process to link up. It is thus encouraged to either have auto-negotiation on for both PHYs or manual configuration for both PHYs.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Expert 5500 points

    Hi Gerome,

    Thank you for explain. 

    Regards,

    John

  • 0 in reply to Gerome Cacho
    TI__Expert 5500 points

    Hi Gerome,

    Customer told me the other side of equipment is out of their control. Their equipment must work with different vendor's equipment. The current issue is if the other side equipment work at force mode, and their equipment is enabled Auto Negotiation, while the negotiation result is always 10Mbps mode. However, based on 802.3 standard, though in this condition, the equipment should be able to be negotiated at 100Mbps/half duplex mode. Why our DP83822 cannot achieve this? Cann't it support parallel detection?

    Regards,

    John

  • 0 in reply to John11513
    TI__Mastermind 32485 points

    Hi John,

    It just occurred to me that if a device is disabling auto-negotiation, then they must also force MDI(X). If DP83822 is the device which is forced speed, please disable auto-MDIX (Reg 0x19[15]). Bit[14] may need to toggle as necessary. This has been recreated in lab with a DP83822 with DP83825 EVMs.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Expert 5500 points

    Hi Gerome,

    Thank you! I will have engineer done the test you mentioned.

    The reason why customer has such kind of requirement is that they want their equipment communicates with any other equipment with 100Mbps. They can only control their own equipment, while the partner equipment is out of their control. I am not sure if a 100BASE-TX equipment without auto-negotiation will also disabled for auto-MDIX?

    Thank you!

    John

  • 0 in reply to John11513
    TI__Mastermind 32485 points

    Hi John,

    That is an understandable concern. However, we can only control our equipment. If a device disables their auto-negotiation, it is recommended to also manually force their MDI/x setting. If our device is auto-negotiating, then this is a concern for the link partner to configure.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Expert 5500 points

    Hi Gerome,

    Ok, understand. Is the reason why forcing the link partner's MDI/x setting to make sure correct connection between the two devices? if so can we also forcing DP83822's MDI/x setting and try different Reg 0x19[14] setting?

    Regards,

    John

  • 0 in reply to Gerome Cacho
    TI__Expert 5500 points

    Hi Gerome,

    Engineer told me yes they can build up 100M link through disabling Auto-MDIX and toggling force-MDIX. Though they think this is not convenient for them since their system do not know the status of link partner. They told me the devices from other competitors does not require such kind of operation. It seems DP83822 cannot function Auto-MDIX once it is configured for Auto-Negotiation. Is this the root casue?

    Thank you!

    John

  • 0 in reply to John11513
    TI__Mastermind 32485 points

    Hi John,

    A colleague of mine had wrote an FAQ based off of this: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/1276226/faq-can-auto-negotiation-link-up-with-force-mode-on-100mbps?tisearch=e2e-sitesearch&keymatch=%2525252520user%252525253A511468#

    The intention behind disabling auto-negotiation in the first place is to be able to be in systems where hotpluging is required. Thus, complete knowledge of the system is required (speed, duplex, MDIx). If your customer intends to be compatible with other partners, it is advised that everything is auto-negotiation enabled and if a link partner is not auto-negotiating, then it is on them to configure specifically to handle that edge case.

    Sincerely,

    Gerome