Unexpected CPU cycle count with time.tick_cpu() #179
Description
With a CPU clock of 64 MHz I would expect time.tick_cpu() to overflow after 17 seconds (2^30 / 64_000_000 = 16.77 sec), and for sleep(1000) to take roughly 64 M cycles, however this script yields differnet results:
from microbit import *
import time
def one_sec_cycles():
ticks_start = time.ticks_cpu()
sleep(1000)
ticks_end = time.ticks_cpu()
return ticks_end - ticks_start
def time_to_overflow():
# If this is the first call it will start the counter, so give it some headstart
ticks_start = time.ticks_cpu()
sleep(20)
ticks_start = time.ticks_cpu()
# Wait until it overflows
while ticks_start < time.ticks_cpu():
sleep(1)
time_start = time.ticks_ms()
ticks_start = time.ticks_cpu()
while ticks_start < time.ticks_cpu():
sleep(1)
time_end = time.ticks_ms()
return time_end- time_start
while True:
print("1 sec: {} cycles".format(one_sec_cycles()))
print("time to overflow: {} ms".format(time_to_overflow()))Output:
1 sec: 10834428 cycles
time to overflow: 83293 ms