It is not working! For example, I specify 60 seconds as argument to M5.shutdown(), the program's loop() is still called every ~5 seconds!
Strange: the eInk display is not refreshed... (at all).

Precisely, my loop code

• Gets the RTC time
• Displays it (both Serial and eInk)
• Calls M5.shutdown(60)

The serial monitor shows that loop is called every ~6-7 seconds. Strange, the eInk screen is not refreshed and displays only the first RTC time.

RTC Time 14:07:35
Shutting down for 60 seconds
RTC Time 14:07:41
Shutting down for 60 seconds

Code

#define DELAY_SECONDS 60

void loop() {
  // Get RTC time
  RTC_TimeTypeDef rtcTime;
  M5.rtc.GetTime(&rtcTime);
  
  // Display time
  sprintf(buf, "%02d:%02d:%02d", rtcTime.Hours, rtcTime.Minutes, rtcTime.Seconds);
  InkPageSprite.drawString(10,50,buf);
  InkPageSprite.pushSprite();
  Serial.printf("RTC Time %02d:%02d:%02d\n", rtcTime.Hours, rtcTime.Minutes, rtcTime.Seconds);

  // Sleep
  delay(100);
  Serial.printf("Shutting down for %d seconds\n", DELAY_SECONDS);
  M5.shutdown(DELAY_SECONDS);
}

I tried M5.shutdown(60000), same result. I also tried supplying a rtcTime to shutdown, but it didn't change anything either.

The creation of the sprite is in setup:

void setup() {

  M5.begin(); //Init CoreInk.  
  if( !M5.M5Ink.isInit()) //Init CoreInk screen.
  {
    Serial.printf("[-] M5Ink init failed");  
    while (1) delay(100);
  }

  M5.M5Ink.clear();   // Clear screen. 
  Serial.printf("[+] Clearing eInk screen\n"); 
  delay(1000);

  if( InkPageSprite.creatSprite(0,0,200,200,true) != 0 ){
    Serial.printf("[-] Ink Sprite create failed\n");
  }

  // set RTC time
  RTC_TimeTypeDef rtcTime;
  rtcTime.Hours = 14;
  rtcTime.Minutes = 6;
  rtcTime.Seconds = 0;
  M5.rtc.SetTime(&rtcTime);
  
  Serial.printf("[+] Setup success\n");
}