Forum Discussion

Zarquin's avatar
Zarquin
Icon for Occasional Contributor rankOccasional Contributor
2 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 M...
Ethernet
  • FvM's avatar
    FvM
    2 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.
Zarquin's avatar
Zarquin
Icon for Occasional Contributor rankOccasional Contributor
2 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
2 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.
  • Zarquin's avatar
    Zarquin
    Icon for Occasional Contributor rankOccasional Contributor
    2 years ago

    Hello FvM,

    I see.

    Any idea from which Marvell 88E1111 PHY register I can read the current ethernet speed? I tried register 4_1.11:10, but that was apparently wrong. Now I am at a loss.

    • FvM's avatar
      FvM
      Icon for Super Contributor rankSuper Contributor
      2 years ago
      Hi,
      unfortunately I don't have 88E1111 documentation at hand. Sorry.
      • Zarquin's avatar
        Zarquin
        Icon for Occasional Contributor rankOccasional Contributor
        2 years ago

        OK I have found it. Seems to be register 17 (below). And apparently the connection does have 1000Mbps. Because the read register 17 shows: 0xAC00

        So far, everything seems to be right.
        But now I'm really wondering why I can still only receive packets but not send any packets, even though all TX Avalon-ST signals are set correctly in Signal Tap II?
        I am testing with Wireshark. Nothing is coming in and the TX LED on the board is not lit either. Only the RX LED flashes.

        I read about timing issues. https://ethernetfmc.com/docs/user-guide/rgmii-timing/

        But can this really be the reason why nothing is sent at all?

  • Zarquin's avatar
    Zarquin
    Icon for Occasional Contributor rankOccasional Contributor
    2 years ago

    Hi FvM,

    my initial question has been answered.
    I will start a new thread for the TX problem
    Thanks a lot!