How to let ESP32S3 PWM to keep working during lightsleep ?

[stone1706]

Hi everyone,
I use PWM Pin(21) to drive LED back light for my LCD . During light sleep mode, I got a problem ,PWM was shut down ,it cannot work anymore until system got wake up.
How to let ESP32S3 PWM to keep working during lightsleep ? I found there someone said PWM support LEDC feature, but I cannot find anyway to do that ...
what is config could support it ?
thanks.

[scruss]

I don't think ESP32 MicroPython is able to do that currently. LEDC turns off during lightsleep with the clock modes that MicroPython uses.

[stone1706]

It's done .right now ESP32S3 PWM is keep working during lightsleep for me .
thanks .

[mattytrentini]

Is this a MicroPython issue? Is it possible to power LEDC during light sleep on the ESP32? This Espressif forum post suggest that it's not.

If someone can supply an IDF example of powering LEDC under a sleep mode we can consider the possibility of duplicating the method in MicroPython.

[stone1706]

I got this information
"The LED PWM module can use RTC8M_CLK as a clock source when APB_CLK is disabled. In other words,
when the system is in low-power consumption mode (see Power Management Chapter), normal peripherals will
be halted (APB_CLK is turned off), but the LED PWM can work normally via RTC8M_CLK."
code like this below

---

  ledc_timer_config_t ledc_timer = {
    .duty_resolution = LEDC_TIMER_13_BIT, // resolution of PWM duty
    .freq_hz = 100,                      // frequency of PWM signal
    .speed_mode = LEDC_LS_MODE,           // timer mode
    .timer_num = LEDC_LS_TIMER,            // timer index
    .clk_cfg = LEDC_USE_RTC8M_CLK,              // Auto select the source clock
};
ledc_timer_config(&ledc_timer);

ledc_channel_config_t ledc_channel[LEDC_TEST_CH_NUM] = {
    {
        .channel    = LEDC_LS_CH2_CHANNEL,
        .duty       = 0,
        .gpio_num   = LEDC_LS_CH2_GPIO,
        .speed_mode = LEDC_LS_MODE,
        .hpoint     = 0,
        .timer_sel  = LEDC_LS_TIMER
    },
};

---

so... need to config pwm to use RTC8M_CLK , not APB_CLK ???

[robert-hh]

That would be a clock change from 80M to 8M, limiting the upper frequency range of PWM to 4M, excluding it's use to create e.g. the master clock for I2S.

[stone1706]

is it possible to do that ?

I am trying to modify machine_pwm.c file to find a way.

[stone1706]

It's done .
Config ".clk_cfg = LEDC_USE_RTC8M_CLK" ,this is work
and now ESP32S3 PWM is keep working during lightsleep for me .
thanks .

[arweic]

I would like to use this feature in MicroPython too. Is there a plan to implement it and if yes, when and how can I use it?