esp-idf: WPA2: Incorrect initialisation behind slow WiFi connection times? (IDFGH-1520)

Slow WPA2 connection times have long been an issue for many ESP32 users. I think I may have a small clue as to where to look for the problem, and a bandaid to fix it for now. Today I was able to reduce connection time on my home WPA2 network from the usual ~1100ms down to ~350ms (240MHz, CONFIG_LWIP_DHCP_DOES_ARP_CHECK=0). Those times are using Arduino’s millis(), the debug output below might have more meaningful timestamps. All it took was this seemingly redundant fix:

wifi_config_t conf;
esp_wifi_get_config(WIFI_IF_STA, &conf);
esp_wifi_set_config(WIFI_IF_STA, &conf);

Often I get this additional debug output (the indicated line): Without fix:

I (722) wifi: n:11 0, o:1 0, ap:255 255, sta:11 0, prof:1
D (1472) nvs: nvs_set_blob sta.apinfo 700[1B][0m           <-------
I (1522) wifi: state: init -> auth (b0)
I (1532) wifi: state: auth -> assoc (0)
I (1542) wifi: state: assoc -> run (10)
I (1582) wifi: connected with MYSSID, channel 11
D (1582) nvs: nvs_set sta.chan 1 11[1B][0m
D (1582) nvs: nvs_set_blob sta.apinfo 700[1B][0m
I (1592) wifi: pm start, type: 1

D (1592) event: SYSTEM_EVENT_STA_CONNECTED

With fix, for comparison:

I (722) wifi: n:11 0, o:1 0, ap:255 255, sta:11 0, prof:1
I (722) wifi: state: init -> auth (b0)
I (732) wifi: state: auth -> assoc (0)
I (732) wifi: state: assoc -> run (10)
I (782) wifi: connected with MYSSID, channel 11
D (782) nvs: nvs_set sta.chan 1 11[1B][0m
D (782) nvs: nvs_set_blob sta.apinfo 700[1B][0m
I (792) wifi: pm start, type: 1

D (792) event: SYSTEM_EVENT_STA_CONNECTED

That additional “nvs_set_blob sta.apinfo” doesn’t seem to occur every time though, so maybe a red herring. The ~750ms mysterious delay unfortunately does.

In fact, I realised just now that I see this delay and ‘apinfo’ output when no NVS data exists for the current WiFi config. Indeed, if I erase the NVS partition, I’m sure to see this exact behaviour next boot, every time. Maybe WPA2 cryptographic data isn’t being loaded properly on WiFi init so it goes through the whole process with the AP every time?

Whatever it is, this fixes it: esp_wifi_set_config(WIFI_IF_STA, &conf);

Tested with esp-idf (PlatformIO) , esp-idf+Arduino component (PlatformIO), Arduino (Arduino IDE and PlatformIO). IDF Test code:

#include <string.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "esp_system.h"
#include "esp_wifi.h"
#include "esp_event_loop.h"
#include "esp_log.h"
#include "nvs_flash.h"
#include "lwip/err.h"
#include "lwip/sys.h"

/**************************************** */
#define WIFI_SSID        "MYSSID"
#define WIFI_PASSWORD    "MYPASSWORD"
//Comment/Uncomment to toggle fix
#define APPLY_FIX
//Suggest CONFIG_LWIP_DHCP_DOES_ARP_CHECK=0
/**************************************** */

static const char *TAG = "WPA2_FIX";

static esp_err_t event_handler(void *ctx, system_event_t *event)
{
    switch(event->event_id) {
    case SYSTEM_EVENT_STA_START:
        esp_wifi_connect();
        break;
    case SYSTEM_EVENT_STA_GOT_IP:
        ESP_LOGI(TAG, "WiFi Connected. IP: %s", ip4addr_ntoa(&event->event_info.got_ip.ip_info.ip));
        break;
    case SYSTEM_EVENT_STA_DISCONNECTED:
        ESP_LOGI(TAG, "Connection failed");
        break;
    default:
        break;
    }
    return ESP_OK;
}

void app_main()
{
    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);
    
    tcpip_adapter_init();
    ESP_ERROR_CHECK(esp_event_loop_init(event_handler, NULL) );
    wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
    ESP_ERROR_CHECK(esp_wifi_init(&cfg));
    ESP_ERROR_CHECK(esp_wifi_set_mode(WIFI_MODE_STA) );

    wifi_config_t wifi_config;
    ESP_ERROR_CHECK(esp_wifi_get_config(ESP_IF_WIFI_STA, &wifi_config) );
    if(strcmp(WIFI_SSID,(char*)wifi_config.sta.ssid) || strcmp(WIFI_PASSWORD,(char*)wifi_config.sta.password)) {
        ESP_LOGI(TAG, "Setting new WiFi credentials");
        wifi_config_t new_config = {
            .sta = {
                .ssid = WIFI_SSID,
                .password = WIFI_PASSWORD,
            },
        };
        ESP_ERROR_CHECK(esp_wifi_set_config(ESP_IF_WIFI_STA, &new_config) );
    }
    #ifdef APPLY_FIX
    else {
        ESP_LOGI(TAG, "Testing fix");
        ESP_ERROR_CHECK(esp_wifi_set_config(ESP_IF_WIFI_STA, &wifi_config) );
    }
    #endif

    ESP_ERROR_CHECK(esp_wifi_start() );

    ESP_LOGI(TAG, "Connecting...");

    vTaskDelete(NULL);
}