Display corruption when using both ESP32 cores?

[mbariola]

Hi,

I have changed a sketch in which the SSD1306 worked fine to use both cores. At that point, "garbage" started appearing on the screen. Here's the minimal sketch showcasing the issue. I am running the sketch on a ttgo lolin esp32 with an integrated SSD1306 display.

Expected behavior: first line of text on display stays the same, 2nd and 3rd line swap between them (see displayText call in loop() and in core0synchronousOps(), where the order of operands 2 and 3 are swapped)

Actual behavior: garbled pixels on display

compiling sketch on PlatformIO

#include <Arduino.h>
#include <SSD1306Wire.h>
#include <WiFi.h>

#define OLEDRESETPIN 16

const unsigned int checkIntervalMs = 3000; // how often the checker will be called
char DisplayHeader[20] = "HeartBeat";
char DisplayLine1[20] = "WiFi: ?? Ext: ??";
char DisplayLine2[20] = "Router: ?? Net: ??";
// display
SSD1306Wire display(0x3c, 4, 15); // define the display



TaskHandle_t Core0Sync;


// Callback methods prototypes

void diplayText(char[], char[], char[]);
void displayText(char line1[], char line2[], char line3[])
{
  display.clear();
  display.setTextAlignment(TEXT_ALIGN_CENTER);
  display.setFont(ArialMT_Plain_16);
  display.drawStringMaxWidth(64, 0, 128, line1);
  display.setFont(ArialMT_Plain_10);
  display.drawStringMaxWidth(64, 26, 128, line2);
  display.drawStringMaxWidth(64, 42, 128, line3);
  display.display();
}

void core0synchronousOps(void * pvParameters)
{

  for (;;)
  {
      Serial.print("core0synchronousOps running on core ");
      Serial.println(xPortGetCoreID());
      displayText(DisplayHeader, DisplayLine1, DisplayLine2);
    delay(checkIntervalMs);
  }
}


void setup() { 
  Serial.begin(460800);

  // reset & init display
  delay(50);
  Serial.println("Prepping Display...");
  pinMode(OLEDRESETPIN, OUTPUT);   // OLED reset pin
  digitalWrite(OLEDRESETPIN, LOW); // set GPIO16 low to reset OLED
  delay(50);
  digitalWrite(OLEDRESETPIN, HIGH); // while OLED is running, must set GPIO16 in high
  delay(50);
  display.init();
  display.flipScreenVertically();
  display.setFont(ArialMT_Plain_10);
  displayText("HeartBeat", "Initializing.", "Please Stand By...");
  delay(1000);
  xTaskCreatePinnedToCore(
      core0synchronousOps, 
      "Core0Sync",         
      10000,               
      NULL,                
      1,                   
      &Core0Sync,          
      0);                  
}

void loop()
{
  delay(1000);
      Serial.print("loop running on core ");
      Serial.println(xPortGetCoreID());
  displayText(DisplayHeader, DisplayLine2, DisplayLine1);
  delay(checkIntervalMs);
}

[mbariola]

Probably connected to #299

[Rotzbua]

As I understand you run the code on both cores without managing the access. So it works as expected and you corrupt the memory.
Embedded libraries are in general not multi-thread/core enabled because every MCU has its own implementation. You have manage the access to the library, so that there is only 1 core that interacts with the library.

[thijstriemstra]

Thanks for the suggestion @Rotzbua. Was running into same issue and pinning the task to a different core fixed the oled corruption.

[mbariola]

@Rotzbua thanks. I did the same as @thijstriemstra and basically now I have a core which does scheduled activities (incl the OLED refresh) and another for realtime callback based stuff, with some variables read by one core and written by the other to keep a shared state.