STM32F769I-Discovery + ESP8266 WiFi Driver

A lightweight FreeRTOS C driver that connects the STM32F769I-Discovery board to WiFi using an ESP8266 module over UART5 and AT commands.

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Hardware Required

Component	Details
STM32F769I-Discovery	Main board
ESP8266 module	ESP-01 or any ESP8266 breakout
3.3 V power supply	The ESP8266 must be powered at 3.3 V — do not use 5 V
4 jumper wires	TX, RX, RST, GND

Important: The STM32F769I-Discovery GPIO pins are 3.3 V. The ESP8266 is also 3.3 V. No level shifter is needed.

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Wiring

STM32F769I-Discovery          ESP8266
─────────────────────         ───────
PC12  (UART5_TX)      ──────► RX
PD2   (UART5_RX)      ◄────── TX
PJ14  (GPIO output)   ──────► RST
GND                   ──────► GND
3.3 V                 ──────► VCC + CH_PD (enable pin)

Pin locations on the Discovery board (UM2033 Table 14):

Signal	Connector	Pin
UART5_TX	A	12
UART5_RX	D	12
RST GPIO	C	9

CH_PD (also called EN) must be pulled HIGH (3.3 V) for the ESP8266 to turn on.

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How It Works

1. AT Commands

The ESP8266 is controlled entirely through AT commands sent over UART at 115200 baud. Each command is a plain text string ending with \r\n. The module responds with OK, ERROR, or specific status strings.

Key commands used by this driver:

AT Command	Purpose
AT	Check module is alive
ATE0	Disable echo
AT+GMR	Read firmware version
AT+RST	Software reset
AT+CWMODE=1	Set station mode (client, not AP)
AT+CWAUTOCONN=0	Disable auto-connect on boot
AT+CWJAP="ssid","pass"	Join a WiFi network
AT+CIFSR	Read assigned IP address

2. FreeRTOS Task

esp_init() creates a dedicated FreeRTOS task (ESP, priority 3, 2048-word stack). That task:

1. Detects the module — tries baud rates 115200 / 9600 / 57600 / 38400 automatically, resets the module via the RST pin, reads firmware version
2. Connects to WiFi — sends AT+CWJAP and waits up to 30 seconds for WIFI GOT IP
3. Enters the main loop — listens for runtime reconnect requests on a FreeRTOS queue

3. Non-blocking API

All public functions are non-blocking. The caller submits a request to a FreeRTOS queue and returns immediately. The ESP task picks it up in the background.

Your application task          ESP task (background)
──────────────────────         ──────────────────────────────
esp_connect_wifi_async() ───► puts credentials on wifi_queue
                               xQueueReceive → wifi_connect_to()
esp_wifi_status()        ◄─── reads s_wifi_status (volatile)

4. Log Ring Buffer

The driver writes human-readable status messages to a ring buffer (24 × 80 chars). Poll it from your application with esp_log_read() to display progress on an LCD, serial terminal, or anywhere else.

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Quick Start

Step 1 — Configure credentials

Edit firmware/esp_config.h:

#define ESP_WIFI_SSID   "YourNetworkName"
#define ESP_WIFI_PASS   "YourPassword"

Step 2 — Add files to your build

In your CMakeLists.txt:

target_sources(your_target PRIVATE
    firmware/esp8266.c
)

target_include_directories(your_target PRIVATE
    firmware/
)

Step 3 — Call esp_init() before vTaskStartScheduler()

#include "esp8266.h"

int main(void)
{
    HAL_Init();
    esp_init();                     // starts the ESP FreeRTOS task
    xTaskCreate(your_task, ...);
    vTaskStartScheduler();
    return 1;
}

Step 4 — Poll status from your task

char log[80];
while (esp_log_read(log, sizeof(log)))
    printf("[ESP] %s\r\n", log);    // or show on LCD

if (esp_wifi_status() == ESP_WIFI_CONNECTED) {
    // WiFi is up — do something
}

See examples/connect_wifi/main_example.c for a complete working example.

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API Reference

Initialisation

void esp_init(void);

Sets up UART5, GPIO (TX/RX/RST), FreeRTOS queues, and starts the ESP task. Call once before vTaskStartScheduler().

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WiFi

void esp_connect_wifi_async(const char *ssid, const char *password);

Submits a WiFi connect request. Non-blocking — the ESP task handles it in the background. Can be called at any time to switch networks.

EspWifiStatus esp_wifi_status(void);

Returns the current connection state. Safe to call from any task.

typedef enum {
    ESP_WIFI_DISCONNECTED = 0,
    ESP_WIFI_CONNECTING,
    ESP_WIFI_CONNECTED,
} EspWifiStatus;

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Logging

int esp_log_read(char *buf, int maxLen);

Reads one log message from the ring buffer. Returns 1 if a message was available, 0 if the buffer was empty. Call in a loop to drain all pending messages.

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Configuration Reference (esp_config.h)

Define	Default	Description
ESP_UART	UART5	UART peripheral
ESP_TX_PIN / PORT	PC12	UART TX pin
ESP_RX_PIN / PORT	PD2	UART RX pin
ESP_RST_PIN / PORT	PJ14	Hardware reset pin
ESP_BAUD	115200	Initial baud rate (auto-detected if wrong)
ESP_WIFI_SSID	"YOUR_WIFI_SSID"	Network name
ESP_WIFI_PASS	"YOUR_WIFI_PASSWORD"	Network password

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Troubleshooting

Symptom	Likely cause	Fix
ESP: Module not found	Bad wiring or power	Check TX/RX are not swapped; verify 3.3 V on VCC and CH_PD
WiFi: Wrong credentials	SSID or password wrong	Double-check esp_config.h
WiFi: No IP — check network	Network issue or weak signal	Move closer to the router; check router DHCP
Module detected but WiFi never connects	Auto-connect interfering	The driver sends AT+CWAUTOCONN=0 — if a previous firmware had saved credentials these may conflict; flash a clean AT firmware to the ESP8266
No log output	esp_log_read() not being called	Call it regularly from a task (every 100–500 ms)

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Tested On

• Board: STM32F769I-Discovery (UM2033)
• Module: ESP-01 (ESP8266 with AT firmware v1.7.x)
• STM32Cube FW: F7 V1.17.2
• FreeRTOS: bundled with STM32Cube F7
• Toolchain: arm-none-eabi-gcc 12.3.1

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License

MIT — free to use, modify, and distribute.