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?

[ESP_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

[ESP_Sprite]

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

[stijnb1234]

Code: [Select all] [Expand/Collapse]

1. #define ETH_PHY_ADDR 0
2. #define ETH_PHY_RST_GPIO GPIO_NUM_17
3. #define ETH_PHY_POWER_GPIO GPIO_NUM_2
4. #define ETH_PHY_MDIO_GPIO GPIO_NUM_18
5. #define ETH_PHY_MDC_GPIO GPIO_NUM_23
6.  
7. esp_err_t Ethernet::init() {
8.   esp_err_t err;
9.  
10.   // Turn on LAN8720
11.   gpio_set_direction(ETH_PHY_POWER_GPIO, GPIO_MODE_OUTPUT);
12.   gpio_set_level(ETH_PHY_POWER_GPIO, 1);
13.  
14.   // Initialize the EMAC
15.   eth_esp32_emac_config_t config = ETH_ESP32_EMAC_DEFAULT_CONFIG();
16.   config.smi_mdc_gpio_num = ETH_PHY_MDC_GPIO;
17.   config.smi_mdio_gpio_num = ETH_PHY_MDIO_GPIO;
18.   config.clock_config = {
19.       .rmii = {.clock_mode = EMAC_CLK_EXT_IN, .clock_gpio = EMAC_CLK_IN_GPIO}};
20.  
21.   // Initialize the MAC and PHY
22.   eth_mac_config_t mac_config = ETH_MAC_DEFAULT_CONFIG();
23.   eth_phy_config_t phy_config = ETH_PHY_DEFAULT_CONFIG();
24.   phy_config.phy_addr = ETH_PHY_ADDR;
25.   phy_config.reset_gpio_num = ETH_PHY_RST_GPIO;
26.   mac = esp_eth_mac_new_esp32(&config, &mac_config);
27.   phy = esp_eth_phy_new_lan87xx(&phy_config);
28.  
29.   // Install the driver
30.   esp_eth_handle_t eth_handle = NULL;
31.   esp_eth_config_t eth_conf = ETH_DEFAULT_CONFIG(mac, phy);
32.   err = esp_eth_driver_install(&eth_conf, &eth_handle);
33.   if (err != ESP_OK) {
34.     ESP_LOGE(TAG, "Ethernet driver installation failure: %s",
35.              esp_err_to_name(err));
36.     return err;
37.   }
38.  
39.   // Initialize TCP/IP network interface
40.   err = esp_netif_init();
41.   if (err != ESP_OK) {
42.     ESP_LOGE(TAG, "Network Interface initialization failure: %s",
43.              esp_err_to_name(err));
44.     return err;
45.   }
46.   err = esp_event_loop_create_default();
47.   if (err != ESP_OK) {
48.     ESP_LOGE(TAG, "Event loop creation failure: %s", esp_err_to_name(err));
49.     return err;
50.   }
51.   esp_netif_config_t netif_config = ESP_NETIF_DEFAULT_ETH();
52.   esp_netif_t* eth_netif = esp_netif_new(&netif_config);
53.   err = esp_netif_attach(eth_netif, esp_eth_new_netif_glue(eth_handle));
54.   if (err != ESP_OK) {
55.     ESP_LOGE(TAG, "Network Interface attachment failure: %s",
56.              esp_err_to_name(err));
57.     return err;
58.   }
59.  
60.   // Register event handlers
61.   err = esp_event_handler_register(ETH_EVENT, ESP_EVENT_ANY_ID, &on_eth_event,
62.                                    NULL);
63.   if (err != ESP_OK) {
64.     ESP_LOGE(TAG, "Ethernet event handler registration failure: %s",
65.              esp_err_to_name(err));
66.     return err;
67.   }
68.   err = esp_event_handler_register(IP_EVENT, IP_EVENT_ETH_GOT_IP, &on_got_ip,
69.                                    NULL);
70.   if (err != ESP_OK) {
71.     ESP_LOGE(TAG, "IP event handler registration failure: %s",
72.              esp_err_to_name(err));
73.     return err;
74.   }
75.  
76.   // Start the Ethernet driver
77.   err = esp_eth_start(eth_handle);
78.   if (err != ESP_OK) {
79.     ESP_LOGE(TAG, "Ethernet start failure: %s", esp_err_to_name(err));
80.     return err;
81.   }
82.  
83.   return ESP_OK;
84. }

GeSHi © Codebox Plus Extension

[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.

[ESP_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.