WiFi-fast_scan例程分析

esp32支持两种扫描方法：fast scan（快速扫描），all channel scan（全信道扫描）

fast scan：在这个模式下，当匹配到的AP被扫描到后就结束扫描，即使信道没有被完全扫描到。你可以设置信号强度的阈值，以及选择AP提供大所需身份验证模式。WiFi驱动会忽略不符合上述条件的AP
all channel scan：只有在所有信道都被扫描之后才会结束扫描；WiFi驱动会存储4个完美匹配的AP。适用于AP的排序方法包括rssi和authmode。扫描完成后，WiFi驱动会选择经过排序后最合适的AP

默认扫描模式为fast scan

扫描结束后，WiFi驱动会尝试连接。因为需要为存储匹配AP分配宝贵的动态存储，并且大多数情况下，会连接到最强的那个AP，因此不需要存储所有匹配到的AP。为了限制动态存储的使用，匹配AP的存储数被限制为4个。在这4个匹配项中，允许AP携带相同的SSID和所有可能的身份验证方式，包括Open, WEP, WPA和WPA2

/* Scan Example

   This example code is in the Public Domain (or CC0 licensed, at your option.)

   Unless required by applicable law or agreed to in writing, this
   software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
   CONDITIONS OF ANY KIND, either express or implied.
*/

/*
    This example shows how to use the All Channel Scan or Fast Scan to connect
    to a Wi-Fi network.

    In the Fast Scan mode, the scan will stop as soon as the first network matching
    the SSID is found. In this mode, an application can set threshold for the
    authentication mode and the Signal strength. Networks that do not meet the
    threshold requirements will be ignored.

    In the All Channel Scan mode, the scan will end only after all the channels
    are scanned, and connection will start with the best network. The networks
    can be sorted based on Authentication Mode or Signal Strength. The priority
    for the Authentication mode is:  WPA2 > WPA > WEP > Open
*/
#include "freertos/FreeRTOS.h"
#include "freertos/event_groups.h"
#include "esp_wifi.h"
#include "esp_log.h"
#include "esp_event.h"
#include "nvs_flash.h"

/* Set the SSID and Password via project configuration, or can set directly here */
//目标AP的名字和密码，字符串格式
#define DEFAULT_SSID CONFIG_EXAMPLE_WIFI_SSID
#define DEFAULT_PWD CONFIG_EXAMPLE_WIFI_PASSWORD

//配置扫描方式
#if CONFIG_EXAMPLE_WIFI_ALL_CHANNEL_SCAN
#define DEFAULT_SCAN_METHOD WIFI_ALL_CHANNEL_SCAN
#elif CONFIG_EXAMPLE_WIFI_FAST_SCAN
#define DEFAULT_SCAN_METHOD WIFI_FAST_SCAN
#else
#define DEFAULT_SCAN_METHOD WIFI_FAST_SCAN
#endif /*CONFIG_EXAMPLE_SCAN_METHOD*/

//配置排序方式
#if CONFIG_EXAMPLE_WIFI_CONNECT_AP_BY_SIGNAL
#define DEFAULT_SORT_METHOD WIFI_CONNECT_AP_BY_SIGNAL//按照信号强度排序
#elif CONFIG_EXAMPLE_WIFI_CONNECT_AP_BY_SECURITY
#define DEFAULT_SORT_METHOD WIFI_CONNECT_AP_BY_SECURITY//按照安全方式排序
#else
#define DEFAULT_SORT_METHOD WIFI_CONNECT_AP_BY_SIGNAL//默认按照信号强度排序
#endif /*CONFIG_EXAMPLE_SORT_METHOD*/

#if CONFIG_EXAMPLE_FAST_SCAN_THRESHOLD
#define DEFAULT_RSSI CONFIG_EXAMPLE_FAST_SCAN_MINIMUM_SIGNAL//将信号阈值设置为项目中配置的阈值
#if CONFIG_EXAMPLE_FAST_SCAN_WEAKEST_AUTHMODE_OPEN
#define DEFAULT_AUTHMODE WIFI_AUTH_OPEN
#elif CONFIG_EXAMPLE_FAST_SCAN_WEAKEST_AUTHMODE_WEP
#define DEFAULT_AUTHMODE WIFI_AUTH_WEP
#elif CONFIG_EXAMPLE_FAST_SCAN_WEAKEST_AUTHMODE_WPA
#define DEFAULT_AUTHMODE WIFI_AUTH_WPA_PSK
#elif CONFIG_EXAMPLE_FAST_SCAN_WEAKEST_AUTHMODE_WPA2
#define DEFAULT_AUTHMODE WIFI_AUTH_WPA2_PSK
#else
#define DEFAULT_AUTHMODE WIFI_AUTH_OPEN
#endif
#else
#define DEFAULT_RSSI -127//默认信号阈值设置为满格
#define DEFAULT_AUTHMODE WIFI_AUTH_OPEN//默认身份验证方式设置为open
#endif /*CONFIG_EXAMPLE_FAST_SCAN_THRESHOLD*/

static const char *TAG = "scan";

//时间处理函数
static void event_handler(void* arg, esp_event_base_t event_base,
                                int32_t event_id, void* event_data)
{
    //当出现wifi事件，且状态为WIFI_EVENT_STA_START（wifi启动后的默认状态）时尝试连接AP
    if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_START) {
        esp_wifi_connect();
    //当断开wifi时，重新尝试连接
    } else if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_DISCONNECTED) {
        esp_wifi_connect();
    } else if (event_base == IP_EVENT && event_id == IP_EVENT_STA_GOT_IP) {
        //获取IP地址并打印
        ip_event_got_ip_t* event = (ip_event_got_ip_t*) event_data;
        ESP_LOGI(TAG, "got ip:" IPSTR, IP2STR(&event->ip_info.ip));
    }
}


/* Initialize Wi-Fi as sta and set scan method */
static void fast_scan(void)
{
    ESP_ERROR_CHECK(esp_netif_init());//初始化TCP/IP协议栈
    ESP_ERROR_CHECK(esp_event_loop_create_default());//创建默认事件循环

    wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();//创建wifi的默认配置信息
    ESP_ERROR_CHECK(esp_wifi_init(&cfg));//初始化wifi

    //将事件处理函数注册到wifi事件和Ip事件
    ESP_ERROR_CHECK(esp_event_handler_instance_register(WIFI_EVENT, ESP_EVENT_ANY_ID, &event_handler, NULL, NULL));
    ESP_ERROR_CHECK(esp_event_handler_instance_register(IP_EVENT, IP_EVENT_STA_GOT_IP, &event_handler, NULL, NULL));

    // Initialize default station as network interface instance (esp-netif)
    esp_netif_t *sta_netif = esp_netif_create_default_wifi_sta();
    assert(sta_netif);

    // Initialize and start WiFi
    wifi_config_t wifi_config = {
        .sta = {
            .ssid = DEFAULT_SSID,
            .password = DEFAULT_PWD,
            .scan_method = DEFAULT_SCAN_METHOD,
            .sort_method = DEFAULT_SORT_METHOD,
            .threshold.rssi = DEFAULT_RSSI,
            .threshold.authmode = DEFAULT_AUTHMODE,
        },
    };
    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());
}

void app_main(void)
{
    // Initialize NVS
    esp_err_t ret = nvs_flash_init();
    if (ret == ESP_ERR_NVS_NO_FREE_PAGES || ret == ESP_ERR_NVS_NEW_VERSION_FOUND) {
        ESP_ERROR_CHECK(nvs_flash_erase());
        ret = nvs_flash_init();
    }
    ESP_ERROR_CHECK( ret );

    fast_scan();
}

WiFi-fast_scan例程分析