RP2: time.sleep and time.sleep_ms waking early (but not time.sleep_us)
Port, board and/or hardware
RP2 (Pico 2W)
MicroPython version
MicroPython v1.25.0 on 2025-04-15; Raspberry Pi Pico 2 W with RP2350
Reproduction
sleep:
>>> for _ in range(0, 10): a = time.ticks_us() ; time.sleep(0.002) ; b = time.ticks_us() ; print(b - a) ;
...
1900
1767
1883
1868
1882
1894
1918
1885
1902
1901
sleep_ms:
>>> for _ in range(0, 10): a = time.ticks_us() ; time.sleep_ms(2) ; b = time.ticks_us() ; print(b - a) ;
...
1957
1782
1917
1881
1895
1883
1903
1902
1905
1899
sleep_us:
>>> for _ in range(0, 10): a = time.ticks_us() ; time.sleep_us(2000) ; b = time.ticks_us() ; print(b - a) ;
...
2035
2033
2022
2022
2020
2021
2022
2021
2022
2027
Expected behaviour
Expecting sleep times to be at least the requested duration (except, of course, in the case of an exception being thrown).
Observed behaviour
thread.sleep and thread.sleep_ms wake early for this particular (2ms) duration, but thread.sleep_us does not.
Additional Information
I discovered this because an I2C sensor driver was intermittently failing due to not sleeping long enough when resetting a device (its code follows the sensor specification of waiting 2ms, or at least it tries to).
https://github.com/micropython/micropython/issues/15626 may or may not be related, I don't know nearly enough about micropython at this point to say.
Code of Conduct
Yes, I agree
RP2350 the watchdog timer does not count down while lightsleep is running
Port, board and/or hardware
Raspberry Pi Pico2
MicroPython version
MicroPython v1.25.0 on 2025-04-15; Raspberry Pi Pico2 with RP2350
Reproduction
Copy the following into wdt_lightsleep_2350.py.
from machine import lightsleep, WDT
from time import sleep_ms
wdt = WDT(timeout=5000)
lightsleep(3000)
sleep_ms(3000)
print('Should not print')
sleep_ms(3000)
Do 'mpremote run wdt_lightsleep_2350.py'.
Expected behaviour
Expect the same behavior seen when the lightsleep is replaced with sleep_ms.
File wdt_sleep_ms_2350.py
from machine import lightsleep, WDT
from time import sleep_ms
wdt = WDT(timeout=5000)
sleep_ms(3000)
sleep_ms(3000)
print('Should not print')
sleep_ms(3000)
>> mpremote run wdt_sleep_ms_2350.py
Traceback (most recent call last):
File "/home/picompute/.local/bin/mpremote", line 8, in <module>
sys.exit(main())
Note: most of traceback removed.
This time the print did not execute because the watchdog timer triggered during the second sleep_ms(3000).
Observed behaviour
The print statement does execute and the watchdog timer triggers during the last sleep_ms(3000).
>> mpremote run wdt_lightsleep_2350.py
Should not print
Traceback (most recent call last):
File "/home/picompute/.local/bin/mpremote", line 8, in <module>
sys.exit(main())
Note: most of traceback removed.
Additional Information
I have changes to lightsleep in modmachine.c which fix this problem.
I will prepare a pull request with this fix.
The root cause is the watchdog timer does not count down while lightsleep() is running.
This problem is RP2350 specific and is not seen on RP2040.
Code of Conduct
Yes, I agree