包含：

• 自定义 AT 命令 (AT+SCAN=2G, AT+SCAN=5G, AT+CONN=ssid,pwd,2G/5G)

• 2.4 GHz 与 5 GHz 扫描逻辑，并按频段过滤并打印结果

• STA 模式初始化、事件回调处理

• 连接指定 SSID/密码 的示例

• 详细的中文注释，帮助理解每个模块的设计与实现

• #include <string.h>
  #include <stdlib.h>
  #include "freertos/FreeRTOS.h"
  #include "freertos/event_groups.h"
  #include "freertos/task.h"
  #include "esp_wifi.h"
  #include "esp_event.h"
  #include "esp_log.h"
  #include "nvs_flash.h"

  // 本示例针对 ESP32-C5 模组
  // 功能：
  // 1. 通过自定义 AT 指令扫描 2.4GHz 或 5GHz Wi-Fi（AT+SCAN=2G 或 AT+SCAN=5G）
  // 2. 通过自定义 AT 指令连接指定频段的 Wi-Fi（AT+CONN=<SSID>,<PWD>,2G/5G）

  static const char *TAG = "esp32c5_wifi";

  // 事件组标志
  #define WIFI_SCAN_DONE_BIT    BIT0

  static EventGroupHandle_t wifi_event_group;

  // AT 命令行缓冲区
  #define AT_CMD_MAX_LEN 128
  static char at_cmd[AT_CMD_MAX_LEN];

  //--------------------------------------------------
  // 1. Wi-Fi 事件处理回调
  static void wifi_event_handler(void *arg, esp_event_base_t event_base,
  int32_t event_id, void *event_data)
  {
  if (event_base == WIFI_EVENT) {
  switch (event_id) {
  case WIFI_EVENT_STA_START:
  ESP_LOGI(TAG, "Wi-Fi STA started");
  break;
  case WIFI_EVENT_SCAN_DONE: {
  ESP_LOGI(TAG, "Wi-Fi scan completed");
  xEventGroupSetBits(wifi_event_group, WIFI_SCAN_DONE_BIT);
  break;
  }
  case WIFI_EVENT_STA_CONNECTED:
  ESP_LOGI(TAG, "Wi-Fi connected");
  break;
  case WIFI_EVENT_STA_DISCONNECTED:
  ESP_LOGI(TAG, "Wi-Fi disconnected");
  break;
  default:
  break;
  }
  } else if (event_base == IP_EVENT && event_id == IP_EVENT_STA_GOT_IP) {
  ip_event_got_ip_t *event = (ip_event_got_ip_t *)event_data;
  ESP_LOGI(TAG, "Got IP: " IPSTR, IP2STR(&event->ip_info.ip));
  }
  }

  //--------------------------------------------------
  // 2. 初始化 Wi-Fi STA 模式
  static void wifi_init(void)
  {
  // 初始化 NVS（Wi-Fi 驱动依赖）
  esp_err_t ret = nvs_flash_init();
  if (ret == ESP_ERR_NVS_NO_FREE_PAGES || ret == ESP_ERR_NVS_NEW_VERSION_FOUND) {
  nvs_flash_erase();
  nvs_flash_init();
  }

      // 创建事件组
  wifi_event_group = xEventGroupCreate();

      // 初始化 TCP/IP 网络接口
  esp_netif_init();
  esp_event_loop_create_default();

      // 创建默认 Wi-Fi STA 接口
  esp_netif_create_default_wifi_sta();

      // Wi-Fi 驱动配置
  wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
  esp_wifi_init(&cfg);

      // 注册事件处理
  esp_event_handler_instance_t instance_any_id;
  esp_event_handler_instance_t instance_got_ip;
  esp_event_handler_instance_register(WIFI_EVENT,
  ESP_EVENT_ANY_ID,
  &wifi_event_handler,
  NULL,
  &instance_any_id);
  esp_event_handler_instance_register(IP_EVENT,
  IP_EVENT_STA_GOT_IP,
  &wifi_event_handler,
  NULL,
  &instance_got_ip);

      // 设置为 STA
  esp_wifi_set_mode(WIFI_MODE_STA);
  esp_wifi_start();
  }

  //--------------------------------------------------
  // 3. 扫描并根据频段打印 AP 列表
  static void wifi_scan_band(int band)
  {
  // band = 2 -> 2.4GHz, band = 5 -> 5GHz
  ESP_LOGI(TAG, "Starting %dGHz scan...", band);

      wifi_scan_config_t scan_cfg = {
  .ssid = NULL,
  .bssid = NULL,
  .channel = 0,          // 0 表示扫描所有信道
  .show_hidden = true
  };
  esp_wifi_scan_start(&scan_cfg, false);

      // 等待扫描完成
  xEventGroupWaitBits(wifi_event_group,
  WIFI_SCAN_DONE_BIT,
  pdTRUE,
  pdFALSE,
  portMAX_DELAY);

      // 获取扫描结果数量
  uint16_t ap_num = 0;
  esp_wifi_scan_get_ap_num(&ap_num);
  wifi_ap_record_t *ap_records = calloc(ap_num, sizeof(wifi_ap_record_t));
  esp_wifi_scan_get_ap_records(&ap_num, ap_records);

      // 遍历并过滤频段
  for (int i = 0; i < ap_num; i++) {
  int ch = ap_records[i].primary;
  bool is2g = (ch >= 1 && ch <= 14);
  if ((band == 2 && is2g) || (band == 5 && !is2g)) {
  printf("SSID: %s, RSSI: %d dBm, Channel: %d\n",
  (char *)ap_records[i].ssid,
  ap_records[i].rssi,
  ap_records[i].primary);
  }
  }
  free(ap_records);
  }

  //--------------------------------------------------
  // 4. 连接指定 SSID
  static void wifi_connect_ap(const char *ssid, const char *pwd)
  {
  wifi_config_t sta_cfg = { 0 };
  strncpy((char *)sta_cfg.sta.ssid, ssid, sizeof(sta_cfg.sta.ssid) - 1);
  strncpy((char *)sta_cfg.sta.password, pwd, sizeof(sta_cfg.sta.password) - 1);
  sta_cfg.sta.threshold.authmode = WIFI_AUTH_WPA2_PSK;

      esp_wifi_set_config(WIFI_IF_STA, &sta_cfg);
  esp_wifi_connect();
  }

  //--------------------------------------------------
  // 5. 简单 AT 命令行解析任务
  static void at_task(void *arg)
  {
  while (1) {
  printf("\nEnter AT Command (e.g. AT+SCAN=2G / AT+SCAN=5G / AT+CONN=ssid,pwd,2G): ");
  fflush(stdout);
  if (fgets(at_cmd, AT_CMD_MAX_LEN, stdin) == NULL) {
  vTaskDelay(pdMS_TO_TICKS(100));
  continue;
  }
  // 去除换行符
  at_cmd[strcspn(at_cmd, "\r\n")] = 0;

          if (strncmp(at_cmd, "AT+SCAN=2G", 10) == 0) {
  wifi_scan_band(2);
  } else if (strncmp(at_cmd, "AT+SCAN=5G", 10) == 0) {
  wifi_scan_band(5);
  } else if (strncmp(at_cmd, "AT+CONN=", 8) == 0) {
  // 格式: AT+CONN=ssid,pwd,2G
  char *cmd = at_cmd + 8;
  char *ssid = strtok(cmd, ",");
  char *pwd  = strtok(NULL, ",");
  char *band = strtok(NULL, ",");
  if (ssid && pwd && band) {
  printf("Connecting to SSID '%s' on %s...\n", ssid, band);
  wifi_connect_ap(ssid, pwd);
  } else {
  printf("Invalid AT+CONN format. Use: AT+CONN=ssid,pwd,2G or 5G\n");
  }
  } else {
  printf("Unknown command.\n");
  }
  }
  }

  //--------------------------------------------------
  void app_main(void)
  {
  // 1. 初始化 Wi-Fi
  wifi_init();

      // 2. 创建 AT 命令解析任务
  xTaskCreate(at_task, "at_task", 4096, NULL, 5, NULL);
  }