ESP32 Forum

Posted: **Mon Aug 18, 2025 1:53 pm**

I’m trying to interface the LAN8710A Ethernet PHY with the ESP32-WROVER-E using the RMII protocol.
After several failed attempts, I realized that my ESP32-WROVER module includes onboard PSRAM, which internally occupies GPIO16 and GPIO17. As a result, these pins are not routed out, and I have no way to feed a 50 MHz RMII reference clock into the ESP32.
So does that mean the RMII interface is essentially unavailable on the ESP32-WROVER-E?

Posted: **Mon Sep 01, 2025 10:40 pm**

@AlexandrF I've used ESP32-WROVER with IP101GRI Ethernet, using GPIO0 as RMII_CLKOUT (50MHz ref) - the IP101GRI generates the clock, and ESP32 is configured to listen to the clock. IP101GRI has a 25.000MHz crystal.

My GPIO pinout is:
0 = RMII_CLKOUT (**input** to ESP32 from TXCLK and RXCLK on IP101GRI)
18 = RMII_MDIO
19 = RMII_TXD0
21 = RMII_TXEN
22 = RMII_TXD1
23 = RMII_MDC
25 = RMII_RXD0
26 = RMII_RXD1
27 = RMII_CRSDV
33 = RMII_RESET

The clock GPIO is set in CONFIG_ETH_RMII_CLK_IN_GPIO and I think ONLY value GPIO0 is supported anyway - see esp_eth_mac_esp.h:

Code: Select all

#if CONFIG_IDF_TARGET_ESP32
#if CONFIG_ETH_RMII_CLK_INPUT // IDF-9724
    #define DEFAULT_RMII_CLK_MODE EMAC_CLK_EXT_IN
#if CONFIG_ETH_RMII_CLK_IN_GPIO == 0
    #define DEFAULT_RMII_CLK_GPIO CONFIG_ETH_RMII_CLK_IN_GPIO
#else
    #error "ESP32 EMAC only support input RMII clock to GPIO0"
#endif // CONFIG_ETH_RMII_CLK_IN_GPIO == 0

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