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DP83849C: MAC to Phy loopback

Rochus
Prodigy 150 points
Part Number: DP83849C

Dear DP83849C experts,

I am using the DP83849C phy. I understand that there are 3 types of loopback tests available with this phy. They are:

- Internal BIST test. A pseudo random pattern is generated in the phy and looped from the phy internal TX to the phy internal RX and compared.

- External BIST test. Same as internal BIST above, except the loopback is performed with a ethernet loopback plug that is plugged into the RJ45

- PMD test. A test which loops back data received from the physical layer back into the tx path and in turn back to the physical layer. I presume you would need some sort of device/application that can verify the integity of loopbacked data.

I have two questions in relation to this.

1) Is my description above correct ?

2) Is it not possible to loop back data in the phy that it received from the MAC, such that the MAC receives data it transmitted ?

Kind regards,

Rocco

  • 0
    TI__Mastermind 26320 points

    Hi,

    1) Yes, your understanding is correct.

    2) You can use MII  loopback using register 0x0000 bit[14]

    Regards,
    Geet

  • 0 in reply to Geet Modi
    Prodigy 150 points

    HI Geet,

    I am trying to get MII loopback working. I have the following setting of the Basic Mode Control Register 0x6001.

      I am taking a logical analyser waveform.  From that waveform I do not see the MTXD0-3 data, but not the MRXD0-3. I have attempted to capture on both the MTXEN and MRXDV, as the spec says that in MII loopback synchronisation is lost,  and a dead time of 500us may occur.

    With the Basic Mode Control Register Setting of 0x6100 alone, should I be expect MII loopback to work? Is there any diagnostic data in the registers that gives a hint on why MII loopback is currently not working ?

    I have seen data on the MRXD once but I have failed to see any time since.

    Kind regards,

    Rocco

  • 0 in reply to Rochus
    TI__Mastermind 26320 points

    Hi Rocco,

    You can read the bit and reconfirm that it is intact set. We don't have any other status register to confirm.

    On TX pins, have you checked TX_EN also getting triggered ? Also, given the PHY has two MAC interface. you have to ensure your configuration is for the right port.

    Regards,

    Geet

  • 0 in reply to Geet Modi
    Prodigy 150 points

    Hi Geet,

    Thanks, from that I understand that other than setting the loopback setting for the target port, there is no other setting required.

    I got it working. I  had to add a delay to compensate for the dead time.

    Thanks,

    Rocco