micros counter accuracy

main.ino

void print_deltas(uint32_t t0_millis, uint32_t t0_micros) {
  uint32_t t_m = millis();
  uint32_t t_u = micros();
  Serial.print(t_u - t0_micros);
  Serial.print(", ");
  Serial.println(t_m - t0_millis);
}

void setup() {
  pinMode(D4, OUTPUT);

  Serial.begin(9600);
  delay(2000);
  uint32_t t0_m = millis();
  uint32_t t0_u = micros();

  print_deltas(t0_m, t0_u);   // Relative time 0.
    __disable_irq();
    digitalWrite(D4, HIGH);
    delayMicroseconds(5000);
    digitalWrite(D4, LOW);

  print_deltas(t0_m, t0_u);  // Relative time 5000.
    __enable_irq();
  print_deltas(t0_m, t0_u);  // Relative time still 5000.
}