GPIO4 can't be used for UART when Ethernet is enabled

[stijnb1234]

I'm using an ESP32-WROOM-U. When I try to use GPIO4 for UART when I have Ethernet enabled, it can't get an IP. Why is this? How can I fix this?

[Sprite]

You need to be a bit more specific: the ESP32-WROOM-U is a module that by itself does not have Ethernet capabilities, it needs an external PHY. What hardware are you using that has that module?

[stijnb1234]

I'm using an LAN8720 chip connected by a custom PCB, which works fine when I'm not using GPIO4 for UART.

TX EN: IO21
TX D0: IO19
TX D1: IO22
RX D0: IO25
RX D1: IO26
CRS DV: IO27
MDIO: IO18
MDC: IO23
REF CLK: IO0
RESET: IO17
LAN8720 ON: IO2

[Sprite]

Can you share your code that initializes the Ethernet MAC and the GPIO?

[stijnb1234]

Code: Ethernet.cpp Select all

#define ETH_PHY_ADDR 0

#define ETH_PHY_RST_GPIO GPIO_NUM_17

#define ETH_PHY_POWER_GPIO GPIO_NUM_2

#define ETH_PHY_MDIO_GPIO GPIO_NUM_18

#define ETH_PHY_MDC_GPIO GPIO_NUM_23



esp_err_t Ethernet::init() {

  esp_err_t err;



  // Turn on LAN8720

  gpio_set_direction(ETH_PHY_POWER_GPIO, GPIO_MODE_OUTPUT);

  gpio_set_level(ETH_PHY_POWER_GPIO, 1);



  // Initialize the EMAC

  eth_esp32_emac_config_t config = ETH_ESP32_EMAC_DEFAULT_CONFIG();

  config.smi_mdc_gpio_num = ETH_PHY_MDC_GPIO;

  config.smi_mdio_gpio_num = ETH_PHY_MDIO_GPIO;

  config.clock_config = {

      .rmii = {.clock_mode = EMAC_CLK_EXT_IN, .clock_gpio = EMAC_CLK_IN_GPIO}};



  // Initialize the MAC and PHY

  eth_mac_config_t mac_config = ETH_MAC_DEFAULT_CONFIG();

  eth_phy_config_t phy_config = ETH_PHY_DEFAULT_CONFIG();

  phy_config.phy_addr = ETH_PHY_ADDR;

  phy_config.reset_gpio_num = ETH_PHY_RST_GPIO;

  mac = esp_eth_mac_new_esp32(&config, &mac_config);

  phy = esp_eth_phy_new_lan87xx(&phy_config);



  // Install the driver

  esp_eth_handle_t eth_handle = NULL;

  esp_eth_config_t eth_conf = ETH_DEFAULT_CONFIG(mac, phy);

  err = esp_eth_driver_install(&eth_conf, &eth_handle);

  if (err != ESP_OK) {

    ESP_LOGE(TAG, "Ethernet driver installation failure: %s",

             esp_err_to_name(err));

    return err;

  }



  // Initialize TCP/IP network interface

  err = esp_netif_init();

  if (err != ESP_OK) {

    ESP_LOGE(TAG, "Network Interface initialization failure: %s",

             esp_err_to_name(err));

    return err;

  }

  err = esp_event_loop_create_default();

  if (err != ESP_OK) {

    ESP_LOGE(TAG, "Event loop creation failure: %s", esp_err_to_name(err));

    return err;

  }

  esp_netif_config_t netif_config = ESP_NETIF_DEFAULT_ETH();

  esp_netif_t* eth_netif = esp_netif_new(&netif_config);

  err = esp_netif_attach(eth_netif, esp_eth_new_netif_glue(eth_handle));

  if (err != ESP_OK) {

    ESP_LOGE(TAG, "Network Interface attachment failure: %s",

             esp_err_to_name(err));

    return err;

  }



  // Register event handlers

  err = esp_event_handler_register(ETH_EVENT, ESP_EVENT_ANY_ID, &on_eth_event,

                                   NULL);

  if (err != ESP_OK) {

    ESP_LOGE(TAG, "Ethernet event handler registration failure: %s",

             esp_err_to_name(err));

    return err;

  }

  err = esp_event_handler_register(IP_EVENT, IP_EVENT_ETH_GOT_IP, &on_got_ip,

                                   NULL);

  if (err != ESP_OK) {

    ESP_LOGE(TAG, "IP event handler registration failure: %s",

             esp_err_to_name(err));

    return err;

  }



  // Start the Ethernet driver

  err = esp_eth_start(eth_handle);

  if (err != ESP_OK) {

    ESP_LOGE(TAG, "Ethernet start failure: %s", esp_err_to_name(err));

    return err;

  }



  return ESP_OK;

}

[phatpaul]

Not sure if relevant or helpful, but I previously found that JTAG was unusable when the EMAC is enabled, even though they don't share any pins. I never figured out why, but configured my project with macros to disable EMAC when I need to debug with JTAG.

[ondrej]

That's strange... The only thing which crossed my mind is the GPIO4 can be IO MUXed to EMAC_TX_ER function (see section 4.10 IO_MUX Pad List in TRM). Therefore make sure the GPIO4 is properly configured.