import machine

TIMER_BASE   = 0x40054000
TIMER_TIMEHW = TIMER_BASE + 0x08
TIMER_TIMELW = TIMER_BASE + 0x0C

def read_time_us():
    """64bit systémový čas (1 µs krok)."""
    while True:
        hi = machine.mem32[TIMER_TIMEHW]
        lo = machine.mem32[TIMER_TIMELW]
        if hi == machine.mem32[TIMER_TIMEHW]:
            return (hi << 32) | lo

# test
t0 = read_time_us()
for _ in range(100_000):
    pass
t1 = read_time_us()

print(f"Elapsed: {t1 - t0} µs")