main.c

/* Simplified ESP-NOW Tx */

#include <stdio.h>
#include <string.h>
#include "freertos/FreeRTOS.h"
#include "esp_log.h"
#include "nvs_flash.h"
#include "esp_wifi.h"
#include "esp_now.h"
#include "esp_sleep.h"
#include "esp_system.h"

static const char *TAG = "espnow-tx";
static uint8_t broadcast_mac[ESP_NOW_ETH_ALEN] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };

/* WiFi should start before using ESPNOW */
static esp_err_t wifi_init(void)
{
    tcpip_adapter_init();

    ESP_ERROR_CHECK(esp_event_loop_create_default());

    wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
    ESP_ERROR_CHECK( esp_wifi_init(&cfg) );
    ESP_ERROR_CHECK( esp_wifi_set_storage(WIFI_STORAGE_RAM) );
    ESP_ERROR_CHECK( esp_wifi_set_mode(WIFI_MODE_STA) );
    ESP_ERROR_CHECK( esp_wifi_start());

    ESP_ERROR_CHECK( esp_wifi_set_channel(CONFIG_ESPNOW_CHANNEL, 0) );
    return ESP_OK;
}


/* Always ESP_NOW_SEND_SUCCESS on broadcasting mode */
static void my_espnow_send_cb(const uint8_t *mac_addr, esp_now_send_status_t status) {
    ESP_LOGD(TAG, "Data sent.");
}

/* Can receive data from other modules */
static void my_espnow_recv_cb(const uint8_t *mac_addr, const uint8_t *data, int len) {
    ESP_LOGD(TAG, "Data received");
}


static esp_err_t espnow_init(void)
{
    /* Initialize ESPNOW and register sending and receiving callback function. */
    ESP_ERROR_CHECK( esp_now_init() );
    ESP_ERROR_CHECK( esp_now_register_send_cb(my_espnow_send_cb) );
    ESP_ERROR_CHECK( esp_now_register_recv_cb(my_espnow_recv_cb) );

    /* Add broadcast peer information to peer list. */
    esp_now_peer_info_t *peer = malloc(sizeof(esp_now_peer_info_t));

    memset(peer, 0, sizeof(esp_now_peer_info_t));
    peer->channel = CONFIG_ESPNOW_CHANNEL;
    peer->ifidx = ESP_IF_WIFI_STA;
    peer->encrypt = false;
    memcpy(peer->peer_addr, broadcast_mac, ESP_NOW_ETH_ALEN);
    ESP_ERROR_CHECK( esp_now_add_peer(peer) );
    free(peer);

    return ESP_OK;
}



void app_main()
{
    // Initialize NVS, wifi and esp_now
    ESP_ERROR_CHECK( nvs_flash_init() );
    ESP_ERROR_CHECK( wifi_init() );
    ESP_ERROR_CHECK( espnow_init() );

    char *data = malloc(sizeof(char) * ESP_NOW_MAX_DATA_LEN);

    snprintf(data, ESP_NOW_MAX_DATA_LEN, "Data #%d", (uint8_t)esp_random());
    
    esp_err_t ret = esp_now_send(broadcast_mac, (uint8_t*) data, strlen(data) + 1);
    if (ret != ESP_OK) {
        ESP_LOGE(TAG, "Send error: %d", ret);
    }
    else {
        ESP_LOGI(TAG, "Data sent: %s\n", data);
    }

    esp_now_deinit();
    esp_wifi_stop();

    esp_deep_sleep(CONFIG_ESPNOW_INTERVAL_MS * 1e3);
}