millis() prevents entering to sleep

[lazarevd]

If millis() function appears anywhere in loop(), it prevents enetering to sleep mode. The position of millis() doesn`t matter, it could be after sleep_cpu().
micros() works normally.

#include <avr/sleep.h>
#include <avr/interrupt.h>
#include <avr/power.h>
#define LED PB0

void setup() {
  pinMode(LED, OUTPUT);
  delay(500);
}

void loop() {
  analogWrite(LED, 0);
  delay(200);
  analogWrite(LED, 250);
  delay(200);
  analogWrite(LED, 0);
  system_sleep();
  millis();//commenting this line let attiny13 enter to sleep, if i uncomment it, led blinks continously
}

void system_sleep() {
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sei();
  sleep_cpu();
}

[radiantwave]

millis() in the MicroCore are watchdog timer based.
Do you still need help with this?

WDTCR &= ~(1 << WDTIE); because of the implementation of the millis() function it is necessary to disable the watchdog interrupt before entering sleep mode
WDTCR |= (1 << WDTIE); after waking the cpu from sleep mode it is necessary to enable the watchdog interrupt again, otherwise the millis() function does not work

[lazarevd]

Thank you. After all I used micros() instead of millis(), but i’ll try your solution.
Is it in documentation? May be it’s worth to add it if it’s not.