blink example for MicroCorre using sleep and millis

blink-MicroCore.ino

// blink LED using sleep and millis() on MicroCore
// 2019 Ralph Doncaster freeware

#define LEDPIN 0

#include <avr/sleep.h>

static void sleep_ms(unsigned ms) {
  ms -= 9; // 1/2 millis minimum increment in MicroCore
  unsigned snapshot = (unsigned)millis();
  // SLEEP_MODE_IDLE is default
  do {
    MCUCR = 1 << SE;
    sleep_cpu();
  } while ((((unsigned)millis() - snapshot)) <= ms);
}

void setup() {
  pinMode(LEDPIN, OUTPUT);
}

void loop() {
  sleep_ms(250);
  digitalWrite(LEDPIN, HIGH);
  sleep_ms(750);
  digitalWrite(LEDPIN, LOW);
}