GPIO15 is randomly pulled low after WiFi has started.

[gitpeut]

Hardware:

Board: ESP32 Dev Module
Core Installation/update date: 17-6-2018
IDE name: Arduino IDE 2.8.1
Flash Frequency: 80Mhz
Upload Speed: any.

Description:

For unknown reason, GPIO15 is pulled low after a random time( 20-300ms) after a digitalWrite high. This behaviour starts after event WiFi STA_GOT_IP is received.
This cannot be reliably reproduced by all, some people never experience the issue, others always experience the issue. Even I have a 1/100 chance this behavior does not occur.
I have tried attaching pull-up an pull-down resistors to gpio15, but that makes no difference.
changing pinMode of GPIO15 before or after Wifi is started does not make a difference.
There may be a relation with SSID, password or other local WiFi related parameters, but I have not been able to demonstrate such a relation.
I came across the issue in this project Edzelf/ESP32-Radio#100
Also a similar (or the same) issue is reported here: https://www.esp32.com/viewtopic.php?t=5898
I made a simple reproducer based on the WiFievents example.

Sketch:

/*
 *  Reproduce random low-pull of GPIO15
 *
*/


#include <WiFi.h>

bool BEFORE=1;
bool stat15, gotip=0, write15=0;

const char* ssid     = "*********";
const char* password = "*****************";


void WiFiEvent(WiFiEvent_t event)
{
    Serial.printf("[WiFi-event] event: %d\n", event);

    switch (event)
    {
    case SYSTEM_EVENT_STA_START:
        Serial.printf( "sta_start     GPIO15 : %s\n", digitalRead( 21 ) ? "HIGH":"LOW");
        break;
    case SYSTEM_EVENT_STA_CONNECTED:
        Serial.printf( "sta_connected GPIO15 : %s\n", digitalRead( 21 ) ? "HIGH":"LOW");
        break;
    case SYSTEM_EVENT_STA_GOT_IP:
        Serial.printf( "sta_got_ip    GPIO15 : %s\n", digitalRead( 21 ) ? "HIGH":"LOW");
        Serial.println("WiFi connected");
        Serial.println("IP address: ");
        Serial.println(WiFi.localIP());

        gotip=1;
        
        break;
    case SYSTEM_EVENT_STA_DISCONNECTED:
        Serial.printf( "sta_disconn   GPIO15 : %s\n", digitalRead( 21 ) ? "HIGH":"LOW");
        Serial.println("WiFi lost connection");
        break;
     default:
        Serial.printf( "event %d      GPIO15 : %s\n", event, digitalRead( 21 ) ? "HIGH":"LOW");
        break; 
    }
}


void setup()
{
    Serial.begin(115200);

    // delete old config
    WiFi.disconnect(true);

    delay(1000);
    
    pinMode( 21, INPUT); // GPIO21 connected to GPIO15 to read status 

    if( BEFORE){
      pinMode(15, OUTPUT );
      digitalWrite(15, LOW );
      digitalWrite(15, HIGH );
      write15 = 1;
    }
    
    // Examples of diffrent ways to register wifi events
    WiFi.onEvent(WiFiEvent);

    WiFi.begin(ssid, password);

    Serial.println();
    Serial.println();
    Serial.println("Wait for WiFi... ");
    
}


void loop()
{

    stat15 = digitalRead( 21 );
    Serial.printf( " loop    GPIO15 : %s\n", stat15 ? "HIGH":"LOW");

    if ( write15 )digitalWrite( 15, stat15?0:1 );

    delay(1000);
    if( gotip && !write15 && !BEFORE ){
      Serial.println("got Ip, wait and enable gpio15 for output");
      delay(2000);
      pinMode( 15, OUTPUT);
      write15 = 1;      
    }
}

Debug Messages:

None.

Serial output of sketch gives a hint:

rst:0x1 (POWERON_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0018,len:4
load:0x3fff001c,len:956
load:0x40078000,len:0
load:0x40078000,len:13256
entry 0x40078a90
[D][WiFiGeneric.cpp:304] _eventCallback(): Event: 2 - STA_START


Wait for WiFi... 
 loop    GPIO15 : HIGH
 loop    GPIO15 : LOW
 loop    GPIO15 : HIGH
 loop    GPIO15 : LOW
[D][WiFiGeneric.cpp:304] _eventCallback(): Event: 4 - STA_CONNECTED
[WiFi-event] event: 4
sta_connected GPIO15 : HIGH
 loop    GPIO15 : LOW
[D][WiFiGeneric.cpp:304] _eventCallback(): Event: 7 - STA_GOT_IP
[WiFi-event] event: 7
sta_got_ip    GPIO15 : LOW
WiFi connected
IP address: 
192.168.0.172
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW
 loop    GPIO15 : LOW

Logic analyzer output shows strange behavior:

[gitpeut]

Installed a newer ( the newest?) version using the recently created https://dl.espressif.com/dl/package_esp32_dev_index.json entry in the Arduino boards manager and the issue is solved.
I have tried about 20 times, and tested with both the above reproducer and ESP32 radio.
I cannot reproduce the mentioned behavior anymore. Everything works as expected.
I would be interested to know if this bug (?) was solved intentionally, but if that is not known, fine as well.

[gitpeut]

Closing the issue. It works.