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TMS570LS3137: Using RMII when MDIO disabled

iConduct
Expert 5815 points
Part Number: TMS570LS3137

Hello Team,

My customer is connecting TMS570LS3137 to an ethernet switch IC (Microchip - KSZ8775).   This switch provides either MDIO or SPI interface using the same pins.   The MDIO interface on the switch allows for access to the PHY, while SPI allows full access to all the registers on the switch.  

Would it be possible to disable the MDIO on the TMS570LS3137 (use as GIOs) since the customer has SPI into the software?

Any feedback you can provide would be appreciated.  

Thanks,
Sem

  • 0
    TI__Guru**** 196306 points
    Hello Sem,

    You can use GPIO in bit bang mode to emulate MDIO interface (IEEE 802.3 clause 22 or 45). There is no ready code. We would be glad to assist you in building the emulated MDIO interface. BTW using GPIO to emulate MDIO/MCLK take much more CPU bandwidth.
  • 0 in reply to QJ Wang
    TI__Guru**** 196306 points
    Hello Sem,

    You can also use those two pins (V5, G3) as GPIO. MDIO and MDCLK are muxed with SPI and N2HET.
    1. Configure V5 as N2HET1[25]: PINMMR7[11:8] = b0010
    2. Configure G5 as N2HET1[19]: PINMMR8[11:8] = b0010
  • 0 in reply to QJ Wang
    Prodigy 10 points
    I'm not sure this exactly answers my question. I want to forgo the MDIO interface entirely, not emulate it in bit bang mode. I am replacing it with a SPI interface to Microchip KSZ8775. This will provide direct register access to the switch to get the configuration data needed. I just want to make sure that inside the TI part I have access to insert that data without using the MDIO interface?

    Thanks, Travis
  • 0 in reply to Travis Garrett
    TI__Guru**** 196306 points
    Hello Travis,

    If KSZ8775 supports SPI interface, you can use TMS570 SPI to write/read data to/from KSZ8775 registers, and leave MDIO/MDCLK pins as GPIO.