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DP83822I: MII loopback in RMII

Pascal REGACHE
Prodigy 240 points
Part Number: DP83822I

Hello, i am using the dp83822 configured to operate in RMII slave 50Mhz interface mode.

Enabling the MII lopback (BMCR register, bit 14, all other BMCR bits clear), I have no data returned on the RMII RX while sending on RMII TX.

Is the MII loopback only working with a MII interface only and I need to use a PCS input loopback instead ?

Thxs

Pascal

  • 0
    TI__Mastermind 18425 points
    Hi Pascal,

    MII loopback should send data back in RMII mode as well. Can you try MII loopback by keeping all the other bits of BMCR register in their default state?

    -Regards,
    Aniruddha
  • 0 in reply to Aniruddha Khadye
    Prodigy 240 points

    Hello Aniruddha, thanks for the answer.

    In the meantime, we made several trials and it seems that the MII loopback works (al least for us) only if BMCR is programmed for 100 Mbps speed.

    I guess that trying the register default setting is not good as if the device is pin-programmed in 10Mbps, it won't work.

    Thats is our conclusion. Could you please confirm that the MII loopback with RMII works only for 100Mbps speed setting ?

    Thanks, best regards,

    Pascal

  • 0 in reply to Pascal REGACHE
    Prodigy 240 points

    Hello, as a follow-up to this thread, we have noticed that just clearing bit 14 of BMCR after a loopback does not restore an good operating state of the device.

    Could you please let me know if:

    - the device has to be reset after a MII loopback ? If yes, what kind of reset (there are at least 3 of them)

    - in loopback state, the device is still expecting a well-formed ethernet frame on the RMII interface (preamble, SOF, 64 bytes of data min) or any pattern can be used as a test pattern ?

    Just to clarify, we are using the DP83822 part without a regular MAC, the loopback test uses a preamble + SOF + 32 bytes of data. At the end of the test, clearing the loopback, the device corrupts received data. A powerdown/up cycle using the PWRDN_N pin restores a nominal device operating state.

    Best regards

    Pascal

  • 0 in reply to Pascal REGACHE
    Prodigy 240 points
    Is there somebody to take care of my questions ?
  • 0 in reply to Pascal REGACHE
    TI__Mastermind 26320 points
    Hi,

    Loopback are debug features and recommend hard reset of device. On RMII loopback ( data inserted from MAC on TXDx and loopback on RXDx) any pattern shall be ok.


    Regards,
    Geet