Hello,

I am using Preferences.h to store data on my M5 Stack Paper, such as Wi-Fi credentials, during my application's setup. It was working fine.
During development and testing, I have rewritten the data in Preferences multiple times on this device. However, I recently noticed that new data is no longer being stored in Preferences, even though there is still available space, as confirmed by running the following code.

#include <Preferences.h>
.
.
.

void checkWifiCredentialsAndDecide(){
  preferences.begin("wifiCredentials", false);

 if(debugFlag){
    size_t whatsLeft = preferences.freeEntries();   
    Serial.printf("Available enteries in the namespace table.\n" );
    Serial.println(whatsLeft);
    preferences.putString("test1", "test 1 value"); 
    Serial.println("preferences.getString(test1): " + String(preferences.getString("test1", "Default value")));
 }
.
.
.
}

Output

Available enteries in the namespace table.
127
preferences.getString(test1): Default value // I am expecting to see "test 1 value"

I have read that the NVS (Non-Volatile Storage) has a write cycle limitation of approximately 10,000 to 100,000 cycles.
I have a few questions:
Is there a way to check how many write cycles are remaining?
Can I check if my flash memory is healthy or corrupted?
Is it possible that the flash memory of my M5 Stack Paper has worn out?

Thank you

Hello,
I would like to know if I can run M5stack paper while connected to the battery?
In this case the M5 stack paper will never shutdown, does this damage the M5 stack paper/ESP 32/battery/diaplay etc?

@felmue
Thank you very much for your reply and help.
The code is working now. The M5 paper is now waking up with and without the USB charger connection. :)

Just a quick question. Now we have commented out the below lines, so does that means that the battery will drain out much faster as the M5 paper is in light sleep mode?

M5.shutdown();

M5.disableEXTPower(); 

@felmue Hello,
Thank your for the reply.
I updated the typo and now using the correct GPIO26 pin, but the behavior of E-paper is still the same.

@felmue
Hello,
Today I did some testing with the external button to wakeup the M5 stack paper from the deep sleep mode.
I connect the button at the PORT B of Epaper. please see the attached pictures.

1. Not connected to the charger: The Epaper didn't woke up from the deep sleep, as expected, as you said.

2. Connected with the charger: The Epaper continously keep restarted after executing the shutdown command, until I unplug the button from the PORT B.
   Do you have an idea about this behavior, what is going on with Epaper?

This is the code I am running on Epaper

#include <M5EPD.h>
#include <Arduino.h>

M5EPD_Canvas canvas(&M5.EPD);

#define WAKEUP_PIN_26 26  // GPIO pin on PORT B (G26)
#define WAKEUP_PIN_33 33  // GPIO pin on PORT B (G26)
void setup() {
    wakeupM5OnButtonPressMode();
}

void loop() {
}

void wakeupM5OnButtonPressMode(){  
    M5.begin();
    M5.EPD.SetRotation(90);
    M5.EPD.Clear(true);
    canvas.createCanvas(540, 400);
    canvas.setTextSize(4);

    gpio_hold_dis((gpio_num_t)M5EPD_MAIN_PWR_PIN);
    gpio_deep_sleep_hold_dis();

    // Display battery voltage before shutting down
    Serial.print("\nVoltage before shut down: " + String(M5.getBatteryVoltage() / 1000.0));
    
    // Update the e-ink display with messages
    canvas.drawString("Press button on PORT B to wake up!", 5, 160);
    canvas.drawString("Going to sleep in 5 secs...", 5, 200);
    canvas.pushCanvas(0, 0, UPDATE_MODE_DU4);
    delay(5000);

    // Enter deep sleep
    shutdownEPD();
}

void shutdownEPD() {
    Serial.println("\nShutting down...");
    
    // Display voltage after shutdown (for debugging purposes)
    Serial.print("\nVoltage after shutdown: " + String(M5.getBatteryVoltage() / 1000.0));
    Serial.print("\n*********************************************\n");
    
    // Prepare for deep sleep
    M5.shutdown();                    // Shutdown the display and peripherals
    M5.disableEPDPower();             // Disable e-paper power
    M5.disableEXTPower();             // Disable external power supply
    
    // Configure GPIO for wake-up on button press (PORT B - G26)
    pinMode(WAKEUP_PIN_26, INPUT_PULLUP);  // Enable internal pull-up for stability
    esp_sleep_enable_ext0_wakeup((gpio_num_t)WAKEUP_PIN_33, LOW);  // Wake when pin goes LOW
    
    // Hold power pins to preserve state during deep sleep
    gpio_hold_en((gpio_num_t)M5EPD_MAIN_PWR_PIN);
    gpio_deep_sleep_hold_en();
    
    // Enter deep sleep
    esp_deep_sleep_start();
}

@felmue Thank you very much for your reply.

Hello,
I have understand that the M5 stack paper can wakeup from the shutdown mode by long pressing the side button but sometimes it is not feasible.

Is it possible to configure M5 stack paper in a way that:

1. It will wake up from short press of the side button?
2. It will wake up using Port A, B or C by connecting the external button? e.g this button from M5

Hello,
I am facing the same issue and not able to display the images on to the M5 Paper. I have tried both canvas.drawPngFile(SPIFFS, "/smiley.png", 0, 0);
and canvas.drawJpgFile(SPIFFS, "/smiley.jpg", 0, 0); but no luck.
I already included #include "SPIFFS.h" and initialized SPIFF using M5.begin(true, true, true, true, false);. The png and jpg files are inside the data folder. SPIFFS.open("/smiley.png") is able to open the file however it is not printing any file content on the console.

I think it is required to format the SPIFFS for the first time, as mentioned here so I followed these steps but ESP32 Sketch data upload is not appearing in arduino 2.0.

However I am able to display the png image using canvas.drawPngUrl("http://imageUrl"); but it is taking more time and quite slow.

Could you please help me in understanding what I am doing wrong?
@simonm @felmue

Hello,
I Got the GFX font header file (by converting the Roboto.ttf file). Loaded the font file using canvas.setFreeFont(&Roboto_Medium50pt7b) and then display the text using canvas.printf(textString.c_str());.
It is working fine and display the text properly but when I am giving some special characters äöü then they are not appearing on M5stack paper.
Can someone please guide me what I am doing wrong? Am I missing something?

Thanks

The link to my question can be found here

Hello,
I Got the GFX font header file (by converting the Roboto.ttf file). Loaded the font file using canvas.setFreeFont(&Roboto_Medium50pt7b) and then display the text using canvas.printf(textString.c_str());.
It is working fine and display the text properly but when I am giving some special characters äöü then they are not appearing on M5stack paper.
Can someone please guide me what I am doing wrong? Am I missing something?

Thanks

The link to my question can be found here