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DP83867IR: DP83867 configuration for only 2 pair MDI link partner

Yunjing Wang1
Expert 4970 points

Part Number: DP83867IR

Tool/software:

Hi team,

My customer is using DP83867 to link with their end customer Ethernet Switch, however the link partner RTL8211 only use 2 pair MDI trace connected to the link, their end customer need every PHY connect to it auto-nego as 100Mbps speed. Check below is the link partner connector schematic.

Customer need DP83867 to enable auto-nego because their product need to connect many different devices, so must support auto-nego. However, when connect to above 2 pair MDI link partner, customer need DP83867 auto-nego to 100M rather than 1000M. But the result turns out DP83867 will always nego to 1000Mbps when connect to above link partner RTL8211 , while the link partner RTL8211 nego result is 100Mbps.

Could you pls kindly suggest how DP83867 can auto-nego to 100Mbps when connect to link partner RTL8211 with only 2 pair MDI cable?

Thank you!

Yunjing 

  • 0
    TI__Mastermind 41885 points

    Hi Yunjing,

    One of our Apps engineers will be reviewing this topic and will be responding to you shortly.

    Sincerely,

    Gerome

  • 0 in reply to Gerome Cacho
    TI__Guru**** 185811 points

    Yunjing

    Please make sure the 1000Base-T full-duplex and half-duplex advertised auto-negotiation capabilities in the Configuration Register 1 (CFG1), Address 0x0009, are not configured. If they disabled these bits, do you see DP83867 auto-negotiated at 100Mbps?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    TI__Expert 4970 points

    Hi David,

    We probably need speed opt feature. But with 0x14 reg configure to 0x340/Enable speed-opt & enhance speed opt, we are not able to see speed_opt_status indication at REG0x11 PHY_Status register. May I know why the speed-opt is not performed?

    BTW, mentioned in the original post, the link partner only connect 2 pair twist outside, and those 2 pair twists are connected to DP83867 A & B channel, that means C and D channels should not be detected any energy, the enhance speed opt should works.

    Thanks!

    Yunjing

  • 0 in reply to Yunjing Wang1
    TI__Guru**** 185811 points

    Yunjing

    Once you enable the speed optimization, can you disable the advertisement of 1000Mbps capabilities of the DP83867 in register 0x0009[9:8] as I stated in my previous response? Please make sure to do a software restart afterward by writing 0x4000 to register 0x1F. If you do this, are you able to see it work?

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    TI__Expert 4970 points

    David,

    Even disable the speed optimization, we can make auto-nego to 100Mbps with disabling advertisement of 1000Mbos capabilities of DP83867.

    However, customer cannot accept this kind of setting. Their product need to auto-nego with both 2-pari twisted link partner and normal 4-pair twisted 1000Mbps link partner. 

    If you disbale 1000M advertise ability, the auto-nego cannot work when the link partner is 1000M.

    That's why we need speed optimization feature, could you investigate why speed opt configuration cannot work after we configure 0x14 reg to 0x340?

    We will also try add software restart by writing 0x4000 to register 0x1F, will let you know if it works.

    Thank you!

    Yunjing

  • 0 in reply to Yunjing Wang1
    TI__Guru**** 185811 points

    Yunjing

    The PHY will not be able to detect between the 2-pair twisted partner and normal 4-pair twisted 1G link partner. You will need to add functionality to the driver to attempt to send packet to link partner and then downshift manually if there is no response at 1G speed as a possible solution.

    Thanks

    David