from machine import Timer
import random
import time

tick_cnt = 0

def tick_handler(pin):
    global tick_cnt
    tick_cnt += 1

soft_timer = Timer(mode=Timer.PERIODIC, period=1, callback=tick_handler)

def get_time_since_boot():   
    millis = tick_cnt % 1000
    seconds = int(tick_cnt / 1000)
    minutes = int(seconds / 60)
    hours = int(minutes / 60)
    return hours, minutes, seconds, millis
    
while True:
    time.sleep(random.uniform(0,3))
    h, M, s, m = get_time_since_boot()
    print(f"Time since boot: {h:02}:{M:02}:{s:02}.{m:03}")