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BCM53286 with Optical Fibre SFP via SERDES

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  • 1.  BCM53286 with Optical Fibre SFP via SERDES

    Posted 03-16-2017 02:50 AM


    I'm currently working on a design which uses the BCM53286 managed switch.

    In our system we use the BCM53286 to give us 24 FE ports connected through various means (capacitive / magnetic isolation) to a number of sub-systems, a BCM5482S GPHY interfaced via 2 of the BCM53286 SGMII/SERDES ports for 2 GigaBit switched copper ports (for system daisy-chaining), and the remaining 2 BCM53286 SGMII/SERDES ports connected to 2 optical fibre SFP's which we will use as a dual-redundant fibre uplink (using link aggregation).

    We have no problems when switching between any of the 24 FE ports to the switched GbE copper ports and vice versa, but we are experiencing trouble when trying to switch through the fibre SFP's.

    By default, should the BCM53286 auto-negotiate and recognise the SFP's without any additional register configuration or does the BCM53286 need to be configured to recognise an SFP over SERDES?

    If it does need to be setup specifically for this type of application, could you suggest a recommended configuration procedure for us please?

    UPDATE (23/03/2017):


    Thanks for the replies Ryan. For some reason my browser isn't letting me reply to your responses in the normal manner so i'm adding what I've discovered here to my original post in the hope that it will be useful to others in future.

    Our system switch (BCM53286) interfaces directly via SERDES to two SFP optical fibre modules running at 1.25G alongside an external GPHY (via the remaining SGMII/SERDES GbE switch ports). The switch sync'ed up fine with the GPHY, but did not automatically auto-negotiate with the SFP's. Your suggestion of manually configuring the SERDES ports via the SERDES/SGMII Control 1 Register (Page B9h-BCh: Address 20h-21h, Block 0 - Bits 0 and 4) was one of the first things we tried, but this did not work either.

    However, after much scratching of heads and trawling through the community posts, i came across this thread:

    Re: bcm53262 in unmanaged mode

    If you scroll down to the bottom of the conversation, the last entry by ing_mmfae (29-Apr-2015) makes mention of connecting a BCM53262 SERDES port to an optical fibre module and specifically details how this should be done for this device. Apparently, the GMAC negotiates differently if the SERDES is connected to an optical module (SFP) rather than an external GPHY. The fix is to switch off the 'GPHY_ScanEnable' bit in the 'GigaPort State Override Register' for that particular port - this allows the BCM53262 to sync with the Fibre Module.

    With the 'GPHY_ScanEnable' bit enabled, the switch tries to poll for an external device on the respective port via the management MDIO/MDC pins; if the external module (SFP etc) does not support this interface, or is not connected to the MDIO/MDC pins, then negotiation fails.

    The fix for the BCM5328X devices is exactly the same!! Clear the 'EN_PHY_SCAN' bit (bit 7) for the port in question in the 'GigaPort State Override Register' (Page01h, Address 29h-2Ch) and the switch will automatically sync up with an external 1GB Optical SFP module without any further intervention.

    Don't worry about overriding the 'PHY_POLL_DIS' pin with a pull-up in order to disable polling of external PHY's (as mentioned in the aforementioned post) - clearing the register 'EN_PHY_SCAN' bit overrides the external PHY polling function for the associated port; it also means that other devices connected in the system (GPHY's etc) can sync up automatically without having to enable polling in software.

    Fortunately we found this out pretty quickly, but we still lost a day or two trying to figure it out when time was of the essence. Hopefully this will help others in future!!

    BCM53286 - great device by the way! :-)


    Message was edited by: Darren Loveridge (23/03/2017)


  • 2.  Re: BCM53286 with Optical Fibre SFP via SERDES

    Posted 03-21-2017 09:02 AM


    If you are using 53286 SGMII/SerDes port connecting with SFP fiber module at 1.25 Gbaud operation, it should not need the extra configure to recognise the SFP.

    Please let me know if you have questions.




  • 3.  Re: BCM53286 with Optical Fibre SFP via SERDES

    Posted 03-21-2017 08:51 PM


    By double check again, please configure the below registers.

    Set  Serdes/SGMII PHY reg   in Datasheet:   set  SerDes/SGMII Control 1 Register (Page B9h-BCh: Address 20h-21h, Block0)   bit4=0, bit0=1 to connect SFP for BCM53286 Serdes/SGMII ports.




  • 4.  Re: BCM53286 with Optical Fibre SFP via SERDES
    Best Answer

    Posted 03-23-2017 08:40 AM

    Hi Ryan,

    Just figured out how to reply to your feedback!!

    The solution you suggested did not work - however we have worked it out now.

    Please see my original post (above) - i have appended the original message with the steps required to achieve correct operation. Thanks again...