How to fix emac_esp32_init(): reset timeout

E (443) esp.emac: emac_esp32_init(428): reset timeout
E (443) esp_eth: esp_eth_driver_install(228): init mac failed
```plaintext {filename="esp.emac"}

## Solution

The issue is that you are using the Ethernet MAC with an external RMII clock input (`EMAC_CLK_EXT_IN`), **but no clock is being input on `GPIO0`, which is the *only* GPIO that can be used for the RMII clock input on the ESP32**.

Check the clock using an oscilloscope or logic analyzer. If you do not see a clock signal on `GPIO0`, you need to provide one.

## What exactly is causing the error?

[During `emac_esp32_init()`](https://github.com/espressif/esp-idf/blob/bfe5caf58f742fd35c023335f475114a5b88761e/components/esp_eth/src/mac/esp_eth_mac_esp.c#L547), ESP-IDF will soft-reset the Ethernet MAC peripheral in the ESP32 and subsequently wait for the reset to complete. It will wait for a maximum of 100 milliseconds. If the reset does not complete within this time, the error `reset timeout` is raised.

This is the relevant code snippet [from the ESP-IDF source code](https://github.com/espressif/esp-idf/blob/bfe5caf58f742fd35c023335f475114a5b88761e/components/esp_eth/src/mac/esp_eth_mac_esp.c#L547):

```c {filename="emac_reset_snippet.c"}
emac_hal_reset(&emac->hal);
uint32_t to = 0;
for (to = 0; to < emac->sw_reset_timeout_ms / 10; to++) {
    if (emac_hal_is_reset_done(&emac->hal)) {
        break;
    }
    vTaskDelay(pdMS_TO_TICKS(10));
}
ESP_GOTO_ON_FALSE(to < emac->sw_reset_timeout_ms / 10, ESP_ERR_TIMEOUT, err, TAG, "reset timeout");
```plaintext {filename="how-to-fix-emac-esp32-init-reset-timeout_block4.txt"}