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DP83865 - Loopback mode

Denis ROMAN
Prodigy 40 points
Other Parts Discussed in Thread: DP83865

Hello,

I am facing issue with DP83865 in loopback mode using the RGMII interface.

THe loopback takes place since I can see with a Logic Analyzer that data on MII_Tx data are copied on MII_Rx with a small latency.

However, MII_Rx data as not read by the host.

And I was wondering if the RGMII control signal (like RXDV/ER..) of DP83865 were toggling exactly the same way in loopback as in regular mode, the timing diagrams of datasheet are not clear to me.

I also was wondering if selection of the mode (HP or 3COM) had an impact.

 

Thanks in advance

Denis

  • 0
    TI__Mastermind 31600 points

    Denis,

    The RGMII specification requires some delay on the clock signals in order to achieve the necessary timing.  This delay can be implemented as additional trace delays on the board or internal to the device.  In 3COM mode, the DP83865  implements the clock delay internal to the device.  In HP mode, the delay must be implemented on the board.  Therefore, the selection of HP or 3COM mode can have an impact. I would suggest comparing the DP83865 RGMII timing specifications against those of the MAC. 

    Patrick

  • 0 in reply to Patrick OFarrell
    TI__Mastermind 31600 points

    Denis,

    One additional note, I modified the title of your post to simplify any future searches of the forum.  I hope that the change does not cause any confusion.

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 40 points

    Hi,

    I have a very stupid question but I am wondering if DP83865 is really supporting loopback mode while in RGMII. This is not clearly stated in the DS.

    Thanks in advance

    Denis

  • 0 in reply to Denis ROMAN
    TI__Mastermind 31600 points

    Loopback mode should work.  In fact, testing of the R/G/MII interface timing is one of the intended uses of this interface. 

    Have you attempted loopback in both RGMII modes (HP and 3Com)?  That configuration directly affects the timing and could resolve the issue you are seeing.

    If the RGMII mode setting does not resolve the issue, could you provide a complete dump of the registers?  I would want to see registers 0x00 through 0x1F on register page 0x0.  Some registers latch their values and need to be read twice so please make sure that the registers are read twice and both reads are reported. 

    Patrick

  • 0 in reply to Patrick OFarrell
    Prodigy 40 points

    Hi Patrick,

    see below the registers dump.

    PHY_REG_0 = 6100

    PHY_REG_1 = 7949

    PHY_REG_1 = 794d

    PHY_REG_2 = 2000

    PHY_REG_3 = 5c7a

    PHY_REG_4 = 1e1

    PHY_REG_5 = 0

    PHY_REG_6 = 4

    PHY_REG_6 = 4

    PHY_REG_7 = 1

    PHY_REG_8 = 0

    PHY_REG_9 = 1300

    PHY_REG_A = 0

    PHY_REG_A = 0

    PHY_REG_0F = 3000

    PHY_REG_10 = c840

    PHY_REG_11 = 44e

    PHY_REG_12 = e000

    PHY_REG_13 = 1

    PHY_REG_14 = 0

    PHY_REG_15 = 0

    PHY_REG_16 = 0

    PHY_REG_17 = 0

    PHY_REG_18 = 0

    PHY_REG_19 = 0

    PHY_REG_1A = 8000

    PHY_REG_1B = 0

    PHY_REG_1C = 0

    PHY_REG_1D = 0

    PHY_REG_1E = 36

    PHY_REG_1F = 0

    I hope it isn't too borrying !!!

    Once again, thanks for your help.

     

    Denis

  • 0 in reply to Denis ROMAN
    Prodigy 40 points

    Hi Patrick,

    I have another about loopback mode.

    Seems the DP83865, does not work in loopback when in 10M.

    It works in 100M, and when it works we realized that bit 2 of register 0x11 (link status) was HIGH after programming PHY while it was 0 when not operating.

    Any particular setting for the 10M loopback to work ?

     

    Thanks in adavance

     

    Denis