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Zarquin's avatar
Zarquin
Icon for Occasional Contributor rankOccasional Contributor
3 years ago
Solved

Can a 1000mbps RGMII TSE communicate with a 100mbps PC?

Dear community,

is it possible to establish an Ethernet connection from Cyclone V Dev Kit to my 100Mbps LAN PC? And if so, what configuration is necessary?

On the FPGA, a Triple Speed Ethernet IP MAC is connected via RGMII to the Marvell 88E1111 PHY on the board.

I have configured the MAC and PHY registers.
MAC Cmd Config: 0x2033 (SW Reset, Pad en, RX en, TX en)
Marvell Ctrl Reg: 0x9140 (SW Reset, 1000 Mbps, Full Duplex)

Do I need to explicitly configure the Marvell Ctrl Register to 100Mbps to establish a 100Mbps connection to my PC or does the PHY do this automatically?

The Marvell has the hardware configuration:

config 0, config 1, config 3 = 000 (PHY Address = 00000, Disable 125MHz clock)

config 2, config 5 = 111 (ANEG =1110 = Auto-Neg, advertise all capabilities, prefer Master)

config 4 = 011 (HWCFG = 1011 = RGMII to copper)

config 6 = 010

Ethernet
  • FvM's avatar
    FvM
    3 years ago
    Hi,
    RGMII reference clocks and data rate changes with ethernet speed and has to switched in MAC. Reading negotiated speed through MI is the usual way to handle it.

9 Replies

  • FvM's avatar
    FvM
    Icon for Super Contributor rankSuper Contributor
    3 years ago
    Hi,
    unless you force a PHY to 1GBPS only, it will autonegotiate the highest available speed with the peer, in this case 100 MBPS. There are a few cases where autonegotiation may fail, e.g. the peer advertizes 100 MBPS but the cable is too bad.
    • Zarquin's avatar
      Zarquin
      Icon for Occasional Contributor rankOccasional Contributor
      3 years ago

      Hi FvM,

      thank you very much for the answer.

      Do I have to adjust the tx_clock to the autonegotiated speed in the PHY?

      More precisely: Do I have to query the speed from the corresponding Marvell PHY register and adjust the tx_clock frequency generated by the FPGA to the actual speed? Or can the tx_clock continue to operate at 125MHz ?

      • FvM's avatar
        FvM
        Icon for Super Contributor rankSuper Contributor
        3 years ago
        Hi,
        yes, RGMII reference clocks and data rate change according to 10/100/1000 ethernet speed.
  • paveetirrasrie_Altera's avatar
    paveetirrasrie_Altera
    Icon for Frequent Contributor rankFrequent Contributor
    3 years ago

    Hi,


    I’m glad that your question has been addressed, I now transition this thread to community support.

    If you have a new question, feel free to open a new thread to get the support from Intel experts.

    Otherwise, the community users will continue to help you on this thread.


    Thank you.