Deinitialize Arduino WiFi Library in ESP32

Using Arduino Programming Questions
1

Hello, I am new to Arduino IDE and also relatively new to microcontroller programming in general. My question is related to programming ESP32 using Arduino WiFi Library. When I run the below sketch, after disconnecting from WiFi, I still see that memory is not freed up. As per my knowledge from the C programming language, after a function call, the stack memory allocated to the function should be freed. I don't see that happening here.

Any comments on this?

#include <WiFi.h>
const char* ssid       = "Radha";
const char* password   = "wifi123456";


void setup()
{
  Serial.begin(115200);
  delay(100);
  Serial.println(esp_get_free_heap_size());
  delay(5000);
  Serial.println(esp_get_free_heap_size());
  //connect to WiFi
  Serial.printf("Connecting to %s ", ssid);
  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
      delay(500);
      Serial.print(".");
  }
  Serial.println(" CONNECTED");
  Serial.println(esp_get_free_heap_size());

  //disconnect WiFi as it's no longer needed
  WiFi.disconnect(true);
  WiFi.mode(WIFI_OFF);
 
  Serial.println(" DISCONNECTED");
   Serial.println(esp_get_free_heap_size());
}

void loop() {
  delay(5000);
  Serial.println("In Loop");
  Serial.println(esp_get_free_heap_size());
}

Result in Terminal

266132
266132
Connecting to Radha .. CONNECTED
214604
 DISCONNECTED
216684
In Loop
216776
In Loop
216776
In Loop
216776
In Loop
216776
2

There are no locals in that function that could be freed.

Probably WiFi.begin() allocates buffers or whatever,
there is no reason to free them only because the user disconnected.

3

@vangaveeti, your topic has been moved to a more suitable location on the forum. Introductory Tutorials is for tutorials that are already written, not for questions.

4

Thanks @Whandall for pointing out. But I couldn't find a function in Arduino WiFi library that will free up the resources. I found the function esp_wifi_deinit() in ESP-IDF that does the job. But I want to know if a similar function is available in Arduino because working with Arduino libraries is much easier.

Thought WiFi.mode(WIFI_OFF) will free the resources but it doesn't.

5

@sterretje Sorry. My Bad.

6

What problem are you trying to solve? What resource do you think need to be "freed" and why?

7

@gfvalvo I need WiFi just to update my RTC. I don't need wifi afterwards. So I don't want WiFi library consuming memory (RAM) once my work (update RTC) is done. That's what I meant by freed. I need RAM for other purposes.

I am able to achieve this by using ESP32-IDF Wifi library as shown below. But the wifi connection is not established. I am working on it.

#include <esp_wifi.h>
#include <time.h>

const char* ntpServer = "pool.ntp.org";
const long  gmtOffset_sec = 3600;
const int   daylightOffset_sec = 3600;

void printLocalTime()
{ 
  char* time_now = NULL;
  struct tm timeinfo;
  if(!getLocalTime(&timeinfo)){
    Serial.println("Failed to obtain time");
    return;
  }
  //String time_n = &timeinfo;
  Serial.printf("Time %d:%d:%d\n",timeinfo.tm_hour,timeinfo.tm_min,timeinfo.tm_sec);
}

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  delay(100);
  Serial.println(esp_get_free_heap_size());
  wifiInit();
  Serial.println(esp_get_free_heap_size());

  configTime(gmtOffset_sec, daylightOffset_sec, ntpServer);
  printLocalTime();
  
  deinitialize_wifi();
  Serial.println(esp_get_free_heap_size());
}

void loop() {
  // put your main code here, to run repeatedly:
}


void wifiInit(){
  wifi_init_config_t confi = WIFI_INIT_CONFIG_DEFAULT();
  wifi_mode_t mod = WIFI_MODE_STA;
  wifi_config_t wifi_config = {
        .sta = {
            {.ssid = "Radha"},
            {.password = "wifi123456"}
        },
    };

  if( esp_wifi_init(&confi) != ESP_OK )
    Serial.println("Failed to Initialise Wifi");
  if( esp_wifi_set_mode(mod) != ESP_OK )
    Serial.println("Failed to Set WiFi mode");
  if( esp_wifi_set_config((wifi_interface_t)ESP_IF_WIFI_STA, &wifi_config) != ESP_OK )
    Serial.println("Failed to set Config");
  if( esp_wifi_start() != ESP_OK )
    Serial.println("Failed to start WiFi");
  else
    Serial.println("WiFi started");
}

void deinitialize_wifi() {
    esp_wifi_stop();
    esp_wifi_deinit();
    Serial.println("Deinitialised Wifi");
}

Result from Terminal

266476
E (617) event: Event loop not initialized via esp_event_loop_init, but esp_event_send called
WiFi started
229912
Failed to obtain time
E (5629) event: Event loop not initialized via esp_event_loop_init, but esp_event_send called
Deinitialised Wifi
260260

As we can see, the free memory after deinitialization using ESP-IDF WiFi library is 260260 bytes compared to 216776 bytes when used Arduino WiFi library. The difference is close to 45,000 bytes. I can use this 45,000 bytes of RAM for my other memory intensive tasks.

So my question is, do we have a function to deinitialization WiFi in Arduino WiFi.h?

8

The Arduino framework for ESP32 is simple to use, but not the best from this side of view.
Anyway, you can mix ESP-IDF functions in your code without problem if you need.

9

Hello @cotestatnt , that's what I am trying to do as I couldn't find a way to deinitialize using the Arduino Library. I found an example that could help me.

10

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