How Can I Accurately Calculate 10 Minutes?

[krishank652]

Dear Community,

I need assistance with calculating time accurately even when the CPU is in sleep mode. How can I achieve this?

When I use millis();, it doesn't work as expected. The increment of milliseconds pauses whenever the CPU enters sleep mode.

Below is the Example

#include <avr/sleep.h>

void RTC_init(void)
{
  /* Initialize RTC: */
  while (RTC.STATUS > 0)
  {
    ;                                   /* Wait for all register to be synchronized */
  }
  RTC.CLKSEL = RTC_CLKSEL_INT1K_gc;     /* 32.768kHz Internal Ultra-Low-Power Oscillator (OSCULP32K) */

  RTC.PITINTCTRL = RTC_PI_bm;           /* PIT Interrupt: enabled */

  RTC.PITCTRLA = RTC_PERIOD_CYC4096_gc /* RTC Clock Cycles 16384, resulting in 32.768kHz/16384 = 2Hz */
                 | RTC_PITEN_bm;                       /* Enable PIT counter: enabled */
}

ISR(RTC_PIT_vect)
{
  RTC.PITINTFLAGS = RTC_PI_bm;          /* Clear interrupt flag by writing '1' (required) */
}


void setup() {
  delay(1000);
  Serial.begin(9600);
 
  RTC_init();                           /* Initialize the RTC timer */
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);  /* Set sleep mode to POWER DOWN mode */
  sleep_enable();
  disableADC();
  SPI0.CTRLA &= ~SPI_ENABLE_bm;
  TWI0.CTRLA &= ~TWI_ENABLE_bm;
  TCA0.SPLIT.CTRLA &= ~TCA_SPLIT_ENABLE_bm;
}
void loop() {
  Serial.println(millis());
for (int i = 0; i <= 600; i++) {
    sleep_cpu();
  }
 Serial.println(millis());
}

[hmeijdam]

Set your PIT so it wakes up the MCU every 1 second.

//Configure PIT
 RTC_PITINTCTRL |= RTC_PI_bm;    // activate PIT Interrupt enable
 RTC_PITCTRLA   |= RTC_PERIOD_CYC32768_gc | RTC_PITEN_bm;// set PIT period and enable

Then use the for loop counter that you already have and let it count to 600. You will then exit your for loop every 10 minutes. You don't need millis()