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DP83822IF: DP83822IF RGMII Ethernet Interface - MDIO requirement?

David Kearney
Intellectual 590 points
Part Number: DP83822IF

Hi Guys,

I'm hoping to use the DP83822IF to interface between my RJ45 twisted pair Ethernet bus and the Zynq7020 RGMII MAC layer. I've just noticed that the MDIO bus (MDIO, MDC) is part of the RGMII protocol and is used for device config and monitoring. I'm wondering will the DP83822IF work OK without the MDIO at it's default settings? Is it capable of detecting speed etc without this interfacing?

Your help would be much appreciated.

Many Thanks,

Dave

  • 0
    Intellectual 590 points
    I've familiarised myself with the DP83822IF IC, and have read up on the HW bootstrapping config capability on startup. So I guess my question has become:

    I'm wondering can I get away with using the IC with the HW bootstrapping config and no MDIO? Are there any critical control or monitoring functions that I would be without if I didn't have access to this bus?

    Many Thanks,
    Dave
  • 0 in reply to David Kearney
    TI__Mastermind 19780 points
    Hi Dave,

    The purpose of the bootstraps is to put the device in a functional mode quickly, or when MDIO is not available. To answer your first question "can I get away with using the IC with the HW bootstrapping config and no MDIO?", the PHY will operate without MDIO configuration.

    To answer your second question "Are there any critical control or monitoring functions that I would be without if I didn't have access to this bus?", maybe.

    The most important monitoring function is determining the speed and duplex of the link that DP83822 has established. If you are in 100base-fx mode, this is not an issue because you will always be in 100M mode. If you are using the copper interface, there is a chance you could connect to a 10M link partner, and then your Zynq will need to know that.

    There are a few ways the Zynq could figure this out: MDIO, in-band status, or monitoring the frequency of the RX_CLK(wont give you link up, or duplex status, only speed). In-band status is a coding that is used on the RX pins when RX_CTRL = 0 on rising and falling edge of RX_CLK.

    Beyond the link up, link speed, or link duplex status, you will not be missing anything critical, and the PHY will send packets as necessary assuming the Zynq MAC driver is happy about your Ethernet connection.

    On the other hand MDIO is an EXCELLENT troubleshooting tool, so I'd recommend connecting it to the Zynq at a minimum.

    Best Regards,
  • 0 in reply to Rob Rodrigues
    Intellectual 590 points
    Many thanks for that detailed explanation Rob - perfect!
  • 0 in reply to Rob Rodrigues
    Intellectual 590 points
    Hi again, I had a quick follow-up Q;

    If I hook up the MDIO bus and have access to that, is having control over the dedicated Reset and PD/Int pins still useful? I see that the MDIO can assert a RESET and an IEEE Power Down - is there any difference between these and the what is achieved by the dedicated control lines? I'd like to minimise my pin count if possible.

    Many Thanks,
    Dave
  • 0 in reply to David Kearney
    TI__Mastermind 23675 points
    Hi David,

    The register access accomplishes the same as the pins do.
    Yes, if you want to avoid use of pins, you can just use MDIO/MDC.

    Best regards,
    Ross