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Do you need a PHY for 1000Base-BX on backplane?

Allan Law
Intellectual 340 points

Hi,

I am finding out how to connect two devices through a backplane using the SGMII module of the C6678.

I would like to know if I need a PHY module to achieve this. If needed, is there a recommendation for this purpose?

Here is what I know so far:

The C6678 has two SGMII ports; SGMII_0 and SGMII_1.

Each of these ports has a pair of SGMII_RXP / SGMII_RXN and SGMII_TXP / SGMII_TXN signals.
If I want to use 1000Base-T with the SGMII, I need to use a PHY module, like the Marvell 88E111,1 to convert these two pairs of TX and RX signals to four pairs of differential signals to be transmitted over the Ethernet cable. From what I understand, this is done to eliminate potential noise that will influence the signals when they are being transmitted through the long Ethernet cables, hence the 1000Base-T standard requires data to be transmitted through four twisted pairs over the Ethernet Cable.

If I want to use SGMII to transfer data through optical fiber, I will need to connect the SGMII_RXP / SGMII_RXN and SGMII_TXP / SGMII_TXN signals to a SFP module.

However, I only need to transfer the data through a backplane, in which there will be minimal noise. This means that I will not need the extra noise cancellation that the 1000Base-T offers, nor do I have to translate the SGMII signals into light medium, which is the case for optical fibers.

Hence, can I connect the SGMII_RXP / SGMII_RXN and SGMII_TXP / SGMII_TXN signals directly into the backplane and into another C6678's SGMII port?

I tried to do some searching on 1000Base-X backplane PHY but I failed to find anything related to it.

Thanks!
Allan 

  • 0
    TI__Mastermind 30825 points

    SGMII to SGMII connection is supported w/ Autonegotiation.  This is discussed in the 'Keystone Architecture Gigabit Ethernet Switch Subsystem UG' http://www.ti.com/lit/ug/sprugv9b/sprugv9b.pdf

    Best Regards,

    Chad

  • 0 in reply to Chad Courtney
    Intellectual 340 points

    Hi Chad,

    There are some figures shown in section 2.4.3.3, that shows the direct connection between SGMII interfaces.

    However, I would like to clarify if that is the industrial standard for 1000Base-X for backplane where we only need a TX+/- and RX+/- given by the SGMII interface.

    I have difficulties finding the standard for 1000Base-X over a backplane and I was wondering if the method shown in figure 2-9 and 2-10 will work, in which there is no need for a PHY when we are transmitting over a backplane.

    Thanks for your help.

    Allan

  • 0 in reply to Allan Law
    TI__Mastermind 30825 points

    1000Base-X is over fiber.  It's a bit outside my knowledge range but maybe you really meant something else.

    You would need to go across a backplane that supported SerDes links if you're going across a backplane board to board and are connecting via SGMII MAC to MAC.  You may also want to look at the HW Design Guidelines for HW implementation details http://www.ti.com/lit/an/sprabi2b/sprabi2b.pdf

    Best Regards,

    Chad

  • 0 in reply to Chad Courtney
    Intellectual 530 points

    Hi Chad,

    I have a customer that is having a hard time getting his 6678 connect to an SGMII-GMII bridge (Max24288). They are using an example from TI’s PDK package, namely the “pdk_C6678_1_1_2_6_old\packages\ti\drv\exampleProjects\PA_emacExample_exampleProject”, to configure the SGMII interface of the 6678.  The example was modified to use the SGMII 0 port instead of  SGMII 1.  That is pretty much the only difference from the original source from TI. However:

    • They are able to perform both internal SGMII and SERDES loopbacks within the DSP but not outside the DSP.
    • They are able to perform GMII loopbacks within the MAX24288 chip.
    • They cannot get any traffic to pass from the TI DSP (SGMII) to the SGMII interface chip (MAX24288).

    I consulted the doc you recommended ( http://www.ti.com/lit/ug/sprugv9b/sprugv9b.pdf) in this ticket but I don't see anything that could help; However I could not figure out if the 6678 expected the interface chip to be in SGMII master or Slave mode?

     Could you possibly have someone review the SGMII port 1 to SGMII port 0 change that my customer did on the TI example code please? You might have some suggestions to make this work.

    Please advise as I need help on this issue badly.

    Thanks
    Electrons4me

  • 0 in reply to Electrons4me
    TI__Mastermind 30825 points

    Can you please create a new E2E thread on this?  This is a bit of a different subject and it's better to start a new thread and get the correct people to look at it.

    Best Regards,

    Chad