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DP83869HM: Loopback mode

Noriyuki Takahashi
Genius 11020 points
Part Number: DP83869HM

Hi team

Please let me ask about loopback mode.

1. Is it possible to use loopback mode with RGMII & 1000Base-T?

2. Could you tell the registers that they need to change in order to turn on loopback mode?

3. Does DP83869HM support Near-End Loopback? It seems that the Loopback Configuration Register (LOOPCR) doesn't exist in the register map.

Regards,

Noriyuki Takahashi

  • 0
    TI__Genius 11725 points

    Hi Noriyuki,

    1. Yes loopback modes are available in the RGMII to 1000Base-T mode. You may review Table 4. Loopback Availability Exception to view the loopbacks that are not available in each of the operational modes.

    2. Most loopback modes are available via register 0x16.

    3. Near end loopback shall be available via register 0x16. Section 9.3.4 discusses the different near-end loopback modes available. 

    Thank you,

    Nikhil

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

  • 0 in reply to Nikhil Menon
    TI__Genius 11020 points

    Nikhil

    Thanks!

    Please let me make sure my understanding.

    Does Near-End Loopback include MII Loopback,  PCS Loopback, Digital Loopback, Analog Loopback and External Loopback?

    Is Far-End (Reverse) Loopback included in  Near-End Loopback?

    I am still not sure about the Loopback Configuration Register (LOOPCR), address 0x00FE, though there is a description as below in the datasheet P.27. How should we understand this?

    "When configuring loopback modes, the Loopback Configuration Register (LOOPCR), address 0x00FE, should be set to 0xE720."

    Regards,

    Noriyuki Takahashi

  • +1 in reply to Noriyuki Takahashi
    TI__Genius 11725 points

    Hi Noriyuki,

    The write to register 0xFE shall only be required if there are issues with writing the loopback mode in register 0x16, though I suspect you will only need to write to register 0x16. Additional info on register 0xFE shall be included in the next revision of the datasheet. 

    Far End (Reverse) loopback is the opposite data path from Near-End Loopback. Reverse loopback will take data from the cable side and send it back across the cable. The near end loopbacks set the PHY to receive data from the MAC interface and send it back to the MAC. If you are able to try the different loopback types, you can identify which block within the PHY is causing the issue.

    Please let me know if you have any further questions regarding loopback modes.

    Thank you,

    Nikhil

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).

  • 0 in reply to Nikhil Menon
    TI__Genius 11725 points

    Hi Noriyuki,

    Please let me know if you have any further questions. Else I will be closing this thread.

    Thank you,

    Nikhil

    All information in this correspondence and in any related correspondence is provided “as is” and “with all faults”, and it is subject to TI’s Important Notice (http://www.ti.com/corp/docs/legal/important-notice.shtml).