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RGMII Interface Between Two C6472 DSPs Through a Board-to-Board Connector

Josh King
Prodigy 190 points

Hi,

 

I am working on a modular design with C6472 DSPs. There is one DSP per module and the modules can communicate with each other through a board-to-board connector. I need to connect the EMAC modules between the DSPs to enable data transfer, but I am not sure what method to use for this connection. The distance between the DSPs will be less than 10 inches. I have been looking into the following options.

 

1) Connect the RGMII interface pins directly through the connector. The direct RGMII connection was described in http://e2e.ti.com/support/dsp/c6000_multi-core_dsps/f/439/p/50706/186795.aspx#186795, but I am not sure if the connector and the routing distance will cause problems.

2) Connect to a PHY through RGMII and route the 4 signal pairs from the PHY (without the magnetics) through the connector.

3) Use a chip such as the Marvell 88E1111 to convert the RGMII interface to SGMII and route the SGMII signals through the connector.

 

I would appreciate any suggestions regarding the above options or if there are any other alternatives that are not listed.

 

Thanks,

Josh King

  • 0
    TI__Mastermind 42545 points

    While connecting RGMII between two C6472 is an acceptable solution the routing of the RGMII interface has to be done carefully.  As far as the options you suggested my comments are below.

    1) Direct routing of the RGMII through a connector is possible but through a connector with 10" of trace would be difficult.  You would have to be extremely careful in matching your trace lengths and use a better quality connector to have a chance getting this to work.  Even then it's difficult to predict whether you would be successful.  RGMII just wasn't intended for that type of connection.

    2) If you're willing to put down the PHY this is the best solution.  Ethernet technology is proven and robust and you should be able to route the signals to the daughtercard without any problem and without using a special connector.

    3) Although you could certainly route SGMII though a connector the higher speed would require a better quality connector and your routing would be more difficult.  If you're willing to put down a component to do RGMII to SGMII you may as well put down the Ethernet PHY.  I'm guessing that you will have more options for Ethernet PHYs and that the PHY is a cheaper solution.

    The only other option I could suggest would be using an SRIO connection.  You would have the same restritions on routing and connectors that SGMII would need but you eliminate that RGMII to SGMII convertion.  Of coarse you would have to modify the software to use the SRIO interface instead of the EMAC interface as well.