ESP32-S3 PWM in lightsleep mode does not works as expected

[yoann-darche]

Port, board and/or hardware

ESP32S3

MicroPython version

MicroPython v1.26.0 on 2025-08-09; Generic ESP32S3 module with ESP32S3

Reproduction

import esp32
from machine import Pin, I2C, ADC, Timer, PWM, deepsleep, lightsleep
from neopixel import NeoPixel
import time

# Internal Led
INTERNAL_LED = const(47)

PWM_PIN_NORMAL = 1
PWM_PIN_SLEEP  = 12

# Init
LED = NeoPixel(Pin(INTERNAL_LED, Pin.OUT), 1)



# Test 26 Version
#    On ESP32-S3 : the pwm_ligthsleep goes to 1 when ligthsleep


pwm1 = PWM(Pin(PWM_PIN_SLEEP), freq=5000, duty_u16=32768, lightsleep=True)
pwm0 = PWM(Pin(PWM_PIN_NORMAL), freq=5000, duty_u16=32768)


# Init : LED = Blue
LED[0] = (0,0,32)
LED.write()

time.sleep_ms(10*1000) # Wait 10 Sec

while True:
    
    LED[0] = (32,0,0) # Green
    LED.write()
    time.sleep_ms(10*1000) # Wait 10 Sec
    
    LED[0] = (0,64,0) # Red
    LED.write()
    lightsleep(10*1000)

Expected behaviour

The option set on the pwm1 instance (lightsleep=True) should keep the pwm signal on while the ESP32 is in ligthsleep.
But when performing the test we see that the pwm1 pin goes to high value when the ESP32 enter in ligthsleep.

Observed behaviour

I've worked on this subject (#10854) and (#16102). On my local repository, I reloaded an old firmware with the same machine_pwm.c (ESP port) code as in the current repository, and it is working as expected! I haven’t yet found the difference - maybe it’s related to the IDF framework version ?

Additional Information

No, I've provided everything above.

Code of Conduct

Yes, I agree

[yoann-darche]

I've also check on the ESP32-S2 mini, and I found the same bug.

[yoann-darche]

Ok, I think that I've discovered the root cause. It seems that in the IDF V5.4+ a new property has been added in the ledc_channel_config_t structure used by ledc_channel_config in the function apply_duty() (line #230 of the machine_pwm.c) : ledc_sleep_mode_t.
This new property should be set to LEDC_SLEEP_MODE_KEEP_ALIVE in order to let PWM continue under lightsleep mode, and to LEDC_SLEEP_MODE_NO_ALIVE_NO_PD in normal use.