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AM4376: RMII MAC to KSZ8567 Ethernet Switch BOOTP Not being broadcasted when booting from Ethernet

Tony Spagnolia1
Prodigy 190 points
Part Number: AM4376

Hi there,

We have a design where three AM4376 processors are used and all three processors are desired to boot through a KSZ8567 Ethernet Switch. We have DIP switches to set the processors to boot from RMII and when we power up the board and connect the board to Wireshark with a laptop, we see only one of the three processors (CPU C as labeled in the schematic) broadcast a BOOTP message.

The processor that does send the BOOTP message is connected through a TI PHY (U76 on the schematic) with an MDIO and RMII interface.

The two processors (CPU A and B) that do not send the BOOTP message are connected to the switch through a digital isolator to the RMII interface directly using KSZ8567's Ports 6/7 worded in the datasheet as "individually configurable RGMII/MII/RMII interfaces for direct connection to a host processor/controller". We raised the question of our setup to Microchip for the Ethernet Strapping and wiring first and they have confirmed the wiring is correct. We have scoped the TX/RX/CRS_DEV lines and see data being intermittently sent from the Switch to processor and vice versa which looks like failed auto-negotiation but no BOOTP message makes it through the switch. Another note, an MDIO interface is not wired to the switch for these two ports.

What about the direct connection would cause the BOOTP message not to be broadcasted for the processors? Does the processor need to negotiate using MDIO as well as RMII to send the BOOTP?  I have attached the schematic for review. The Ethernet Switch and RMII connections are on page 13.CORE_Schematic_M0.pdf

  • 0
    TI__Guru**** 161600 points

    Hi,

    Let me check the schematic and I will update the thread with my feedback.

    Best Regards,
    Yordan

  • 0 in reply to Yordan Kovachev
    Prodigy 190 points

    I am starting to believe the lack of the MDIO interface is causing the Processor to fail to auto-negotiate from reading Section 5.2.7.3.1 in the AM437x Technical Reference Manual where it states in the final bullet "Device detects if the PHY is alive on the MDIO interface and ..."

    There is another bullet in the section that states "On a warm reset, if Ethernet reset isolation is enabled, the ROM will skip configuring the EMAC and directly issue the BOOTP request" I can't find any information on how to set up Ethernet reset isolation. How could we set this up so the BOOTP request is sent immediately?