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Lesson17_WiFi_Functions: ESP32-P4 WiFi Three Operating Modes

1. Course Introduction

This lesson uses ESP-IDF to demonstrate the three WiFi operating modes of the ESP32-P4 via the WiFi driver: Station (STA), softAP (AP), and AP+STA (hybrid mode with NAPT forwarding). The course includes three independent projects; learners can compile and flash each one separately to experience every mode. In Station mode, the development board acts as a client connecting to a router; in softAP mode, the development board acts as a hotspot for other devices to connect; in AP+STA mode, the development board simultaneously acts as both a client and a hotspot, and uses NAPT to allow AP clients to access the internet through the STA.

After the program is flashed, the serial monitor outputs the WiFi event log corresponding to the mode (connection success, IP acquisition, station joining or leaving, etc.). Through this experiment, learners will complete the full-link verification of initialization, event handling, and network interface management for the three WiFi modes: STA, AP, and AP+STA.

2. Learning Objectives

  • Be able to open the three Lesson17 projects in ESP-IDF and set the target chip to esp32p4.
  • Be able to explain the differences and applicable scenarios among the three modes: STA, AP, and AP+STA.
  • Be able to explain the workflow of the WiFi event-driven mechanism (WIFI_EVENT/IP_EVENT).
  • Be able to complete the compilation and flashing of all three modes, and observe the serial log to confirm each mode works properly.
  • Be able to connect a phone to the AP in AP+STA mode and access the internet through the development board.

3. Prerequisites

  • Hardware: CrowPanel Advanced 7 / 9 / 10.1 inch ESP32-P4 HMI AI Display development board (one); a USB Type-C data cable that supports data transfer (one); a phone or computer for connecting to the AP for testing.
  • Compatibility note: The hardware and software code for the 7 / 9 / 10.1 inch development boards are fully interchangeable; only the board size differs. Please select the appropriate model based on display size and usage scenario.
  • Software: VS Code, ESP-IDF Extension (ESP-IDF v5.4 or above).
  • Project dependencies: The three projects are ESP32_P4-station, ESP32_P4-softAP, and ESP32_P4-softap_sta, all depending on system components such as esp_wifi and nvs_flash.
  • Network: An available 2.4 GHz WiFi router (required for STA and AP+STA modes); the SSID and password need to be configured in the source code macro definitions.

Code download link:

CrowPanel-Advanced-7inch-ESP32-P4-HMI-AI-Display-1024x600-IPS-Touch-Screen/example at master · Elecrow-RD/CrowPanel-Advanced-7inch-ESP32-P4-HMI-AI-Display-1024x600-IPS-Touch-Screen

4. Software Operation Steps

  1. In VS Code, open the ESP-IDF Extension panel, click Open ESP-IDF Project, and select the ESP32_P4-station folder (Station mode). Opening the Station project

  2. First select the code runtime environment ESP-IDF v5.4.2, set the flashing method to UART, and then select the serial port that actually corresponds to the development board. Then click Set Espressif Device Target in the ESP-IDF Extension panel and select esp32p4. After the setup is complete, the status bar should display ESP-IDF v5.4.2, UART, the required COM port, and ESP32-P4. Confirming ESP-IDF, flashing method, serial port, and target chip

  3. If you need to modify the Station network information, modify EXAMPLE_ESP_WIFI_SSID and EXAMPLE_ESP_WIFI_PASS in main/station_example_main.c. Setting Station mode WiFi information

  4. In the three projects—Station, softAP, and softap_sta—open the SDK Configuration Editor respectively and wait for the configuration page to fully load. Clicking the SDK Configuration Editor

Waiting for the SDK Configuration Editor to finish loading

  1. In the search box, enter hosted and set the SDIO parameters of the onboard ESP32-C6 as follows: Bus Width 4 Bits, Clock 40000 kHz, CMD GPIO 19, CLK GPIO 18, D0/D1/D2/D3 GPIO 17, 16, 15, 14 respectively, and Reset GPIO 32.

This configuration should be verified in all three projects.

Verifying the Hosted configuration in other projects

  1. Search for flash and ensure Flash SPI mode: QIO; Flash Sampling Mode: STR Mode; Flash SPI speed: 80 MHz; Flash size: 16 MB. Configuring Flash parameters

  2. In the LWIP configuration of the AP+STA (softap_sta) project, enable Enable IP forwarding, Enable NAT, and Enable NAT Port Mapping, so that hotspot clients can forward network traffic through the Station side. Enabling forwarding and NAPT for AP+STA

  3. At the same time, confirm that sdkconfig.defaults contains CONFIG_LWIP_IP_FORWARD=y and CONFIG_LWIP_IPV4_NAPT=y, so that forwarding and NAPT are still retained when the configuration is regenerated. Setting AP+STA default configuration

  4. Then refer to "4. Software Operation Steps" in Lesson07_Turn_on_the_Screen to complete the detailed SDK configuration; the relevant configuration methods have been explained in Lesson 7.

  5. After confirming the configuration is correct, click Save in the upper right corner; verify the modifications have been saved, then execute Build to compile.

  6. Click Full Clean to clear the cache left by the previous compilation. Perform this operation after the first compilation, after switching project configurations, or after modifying SDK parameters, so that stale configurations do not affect the new compilation result. Executing Full Clean

  7. Click Build to compile the project. On success, the output Project build complete is displayed. Compiling the Station project

  8. After connecting the development board, click Select Port to Use to choose the corresponding serial port, then click Flash to flash the firmware. After flashing, click Monitor to observe the connection log. Press Ctrl + ] to exit the monitor.

    Flashing and monitoring Station mode

  9. Open the ESP32_P4-softAP project (AP mode), follow steps 2–10 to confirm the target chip, WiFi parameters, Hosted, and Flash configurations, and execute Full Clean, Build, Flash, and Monitor in sequence.

  10. After flashing is complete, the serial port should indicate that AP mode is ready; once a phone or computer connects to the ELECROW hotspot, the serial port will print the client join event and its IP information. This mode only provides a local hotspot and is not connected to an upstream network, so clients cannot access the internet by default.

    Observing the softAP startup log

    Phone connecting to AP+STA hotspot

    image-20260727102034939

  11. Open the ESP32_P4-softap_sta project (AP+STA mode), follow steps 2–8 to confirm the target chip, WiFi parameters, Hosted, Flash, and NAPT configurations, and execute Full Clean, Build, Flash, and Monitor in sequence.

  12. After flashing is complete, the serial port should first show that STA has connected to the upstream WiFi, then show that AP has started; once a phone or computer connects to the ELECROW hotspot, the serial port will print the client IP and it can access the internet through NAPT.

    Observing the AP+STA simultaneous startup log

    Phone connecting to AP+STA hotspot

    Observing the softAP client join log

  13. Finally, you can use the one-click operation button in the ESP-IDF status bar to sequentially execute compilation, flashing, and opening the serial monitor. Use this only after the project configuration, serial port, and code have all been confirmed correct; if you need to locate a problem, still follow the steps above and execute them one by one. One-click compile, flash, and open monitor

5. Hardware Operation Steps

  1. Use a USB data cable to connect the ESP32-P4 development board to the computer. Connecting the development board

  2. After flashing in Station mode, observe whether the serial port prints got ip:192.168.x.x to confirm it has connected to the router and obtained an IP. P4_IDF_17_Images_12

  3. After flashing in softAP mode, use a phone to search for the WiFi hotspot ELECROW, enter the password 12345678 to connect, and the serial port should print station join. Phone connecting to AP+STA hotspot

P4_IDF_17_Images_11

  1. After flashing in AP+STA mode, the STA connects to the router and obtains an IP, while the AP hotspot becomes available; after the phone connects to the AP, it should be able to access the internet (NAPT forwarding), and the serial port will print both AP and STA logs. Phone connecting to AP+STA hotspot

Observing the AP+STA dual-mode log

6. Key Code Explanation

Station Mode

esp_netif_create_default_wifi_sta();
ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_STA));
ESP_ERROR_CHECK(esp_wifi_set_config(WIFI_IF_STA, &wifi_config));
ESP_ERROR_CHECK(esp_wifi_start());

STA mode initialization: create the STA network interface, set STA mode, configure SSID/password, and start WiFi. After startup, the WIFI_EVENT_STA_START event triggers esp_wifi_connect to connect to the router. If the SSID/password is incorrect, after retries reach the upper limit, WIFI_FAIL_BIT will be set.

EventBits_t bits = xEventGroupWaitBits(s_wifi_event_group,
        WIFI_CONNECTED_BIT | WIFI_FAIL_BIT, pdFALSE, pdFALSE, portMAX_DELAY);

This blocks while waiting for the connection result. The IP_EVENT_STA_GOT_IP event sets WIFI_CONNECTED_BIT, and if retries exceed the limit, WIFI_FAIL_BIT is set. portMAX_DELAY means waiting indefinitely until a result is received. This is a typical event-driven implementation.

softAP Mode

esp_netif_create_default_wifi_ap();
ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_AP));
wifi_config_t wifi_config = { .ap = { .ssid = "ELECROW", .password = "12345678", .max_connection = 4, ... } };
ESP_ERROR_CHECK(esp_wifi_set_config(WIFI_IF_AP, &wifi_config));
ESP_ERROR_CHECK(esp_wifi_start());

AP mode initialization: create the AP network interface, set AP mode, configure the hotspot SSID/password/channel/maximum number of connections, and start. After startup, other devices can search for and connect to the ELECROW hotspot. The WIFI_EVENT_AP_STACONNECTED event is triggered when a device connects. If the password is empty, authmode should be changed to WIFI_AUTH_OPEN (open hotspot).

AP+STA Mode (with NAPT)

ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_APSTA));
esp_netif_t *esp_netif_ap = wifi_init_softap();
esp_netif_t *esp_netif_sta = wifi_init_sta();
ESP_ERROR_CHECK(esp_wifi_start());

AP+STA mode runs both AP and STA simultaneously: STA connects to the upstream router and obtains an IP, AP provides a hotspot for downstream devices, and the two network interfaces coexist.

softap_set_dns_addr(esp_netif_ap, esp_netif_sta);
esp_netif_set_default_netif(esp_netif_sta);
esp_netif_napt_enable(esp_netif_ap);

NAPT (Network Address Port Translation) allows devices connected to the AP to access the internet through the STA: it forwards the STA-side DNS to the AP-side DHCP client, sets STA as the default egress, and enables NAPT on the AP interface. If NAPT is not enabled, AP clients can only access the development board itself and cannot reach the internet.

7. Experimental Observations

Station Mode: 

I (xxx) wifi station: ESP_WIFI_MODE_STA
I (xxx) wifi station: wifi_init_sta finished.
I (xxx) wifi station: retry to connect to the AP     (may retry)
I (xxx) wifi station: got ip:192.168.1.100
I (xxx) wifi station: connected to ap SSID:elecrow888 password:elecrow2014

softAP Mode: 

I (xxx) wifi softAP: ESP_WIFI_MODE_AP
I (xxx) wifi softAP: wifi_init_softap finished. SSID:ELECROW password:12345678 channel:1
I (xxx) wifi softAP: station xx:xx:xx:xx:xx:xx join, AID=1   (phone connects)

AP+STA Mode: 

I (xxx) WiFi SoftAP: ESP_WIFI_MODE_AP
I (xxx) WiFi Sta: ESP_WIFI_MODE_STA
I (xxx) WiFi Sta: Station started
I (xxx) WiFi Sta: Got IP:192.168.1.101
I (xxx) WiFi SoftAP: station xx:xx:xx:xx:xx:xx joined, AID=1
In AP+STA mode, after the phone connects to the ELECROW hotspot, it should be able to access the internet (NAPT takes effect). If STA cannot connect to the router, check the SSID/password and signal; if AP clients cannot access the internet, confirm whether NAPT was successfully enabled; if the phone cannot find the hotspot, check the AP's SSID and channel configuration.