A First Example

Setting up a PWM is very simple in theory, but there are a lot of settings in the two structs involved in the configuration. The simplest example is just to generate a PWM signal on a single GPIO line. First we set up the timer:

void app_main(void)
{
  ledc_timer_config_t ledc_timer = {
      .speed_mode = LEDC_LOW_SPEED_MODE,
      .timer_num = 0,
      .duty_resolution = LEDC_TIMER_13_BIT,
      .freq_hz = 4000,
      .clk_cfg =  LEDC_APB_CLK
  };

This selects low-speed timer 0 and sets its counter to 13-bit mode, which counts up to 8,191 before overflowing. The specification of a frequency of 4000Hz and a clock of 80MHz, makes the divider set to 20,000.

Next we set up the channel:

  ledc_channel_config_t ledc_channel = {
      .speed_mode = LEDC_LOW_SPEED_MODE,
      .channel = 0,
      .timer_sel = 0,
      .intr_type = LEDC_INTR_DISABLE,
      .gpio_num = 2,
      .duty = 4096, 
      .hpoint = 0
  };

Again we select a low-speed controller channel 0 and connect it to timer 0 using timer_sel and GPIO 2 with interrupts disabled. The duty is set to 4096, which is roughly half 8191 and so the duty cycle is 50%. The hpoint is set to 0 so the high edge of the output occurs when the timer starts.

To start the PWM on GPIO 2 we need only two function calls:

ledc_timer_config(&ledc_timer);
ledc_channel_config(&ledc_channel);

The complete program is:

#include <stdio.h>
#include "driver/gpio.h"
#include "freertos/FreeRTOS.h"
#include "driver/ledc.h"
void app_main(void)
{
  ledc_timer_config_t ledc_timer = {
      .speed_mode = LEDC_LOW_SPEED_MODE,
      .timer_num = 0,
      .duty_resolution = LEDC_TIMER_13_BIT,
      .freq_hz = 4000,
      .clk_cfg = LEDC_APB_CLK
  };
  ledc_timer_config(&ledc_timer);
  ledc_channel_config_t ledc_channel = {
      .speed_mode = LEDC_LOW_SPEED_MODE,
      .channel = 0,
      .timer_sel = 0,
      .intr_type = LEDC_INTR_DISABLE,
      .gpio_num = 2,
      .duty = 4096, 
      .hpoint = 0
  };
  ledc_channel_config(&ledc_channel);
}

The result is as you would expect:

It is usually simpler to put the configuration details into a function which sets all of the defaults. It is possible to change most of the configuration later. For example:

void PWMconfigLow(int gpio, int chan,
     int timer, int res,
                     int freq, float duty) { 
  ledc_timer_config_t ledc_timer = {
      .speed_mode = LEDC_LOW_SPEED_MODE,
      .clk_cfg = LEDC_APB_CLK
  };
  ledc_timer.timer_num = timer;
  ledc_timer.duty_resolution = res;
  ledc_timer.freq_hz = freq;
  ledc_channel_config_t ledc_channel = {
    .speed_mode = LEDC_LOW_SPEED_MODE,
    .hpoint = 0,
    .intr_type = LEDC_INTR_DISABLE,
  };
  ledc_channel.channel = chan;
  ledc_channel.timer_sel = timer;
  ledc_channel.gpio_num = gpio;
  ledc_channel.duty =((float)(2<<(res-1)))*duty;  
  ledc_timer_config(&ledc_timer);
  ledc_channel_config(&ledc_channel);
}

This function lets you set the timer, channel, frequency, and resolution in the usual way. The only innovation is to allow the duty cycle to be set as a fraction. So for a 50% duty cycle, you would specify 0.5.