LED Control

Introduction

The LED control (LEDC) module is primarily designed to control the intensity of LEDs, although it can be used to generate PWM signals for other purposes as well. It has 16 channels which can generate independent waveforms, that can be used to drive e.g. RGB LED devices.

Half of all LEDC’s channels provide high speed mode of operation. This mode offers implemented in hardware, automatic and glitch free change of PWM duty cycle. The other half of channels operate in a low speed mode, where the moment of change depends on the application software. Each group of channels is also able to use different clock sources but this feature is not implemented in the API.

The PWM controller also has the ability to automatically increase or decrease the duty cycle gradually, allowing for fades without any processor interference.

Functionality Overview

Getting LEDC to work on specific channel in either high or low speed mode is done in three steps:

  1. Configure Timer to determine PWM signal’s frequency and the a number (resolution of duty range).
  2. Configure Channel by associating it with the timer and GPIO to output the PWM signal.
  3. Change PWM Signal that drives the output to change LED’s intensity. This may be done under full control by software or with help of hardware fading functions.

In an optional step it is also possible to set up an interrupt on the fade end.

Key Settings of LED PWM Controller's API

Key Settings of LED PWM Controller’s API

Configure Timer

Setting of the timer is done by calling function ledc_timer_config(). This function should be provided with a data structure ledc_timer_config_t that contains the following configuration settings:

  • The timer number ledc_timer_t and a speed mode ledc_mode_t.
  • The PWM signal’s frequency and a “bit number”. The later represents a resolution of PWM’s duty value changes.

The frequency and the bit values are interdependent. The higher the PWM frequency, the lower bit number is available and vice versa. This relationship may became important, if you are planning to use this API for purposes other that changing intensity of LEDs. Check section Supported Range of Frequency and Bit Number for more details.

Configure Channel

Having set up the timer, the next step is to configure selected channel (one out of ledc_channel_t). This is done by calling function ledc_channel_config().

In similar way, like with the timer configuration, the channel setup function should be provided with specific structure ledc_channel_config_t, that contains channel’s configuration parameters.

At this point channel should became operational and start generating PWM signal of frequency determined by the timer settings and the duty on selected GPIO, as configured in ledc_channel_config_t. The channel operation / the signal generation may be suspended at any time by calling function ledc_stop().

Change PWM Signal

Once the channel is operational and generating the PWM signal of constant duty and frequency, there are couple of ways to change this signal. When driving LEDs we are changing primarily the duty to vary the light intensity. See the two section below how to change the duty by software or with hardware fading. If required, we can change signal’s frequency as well and this is covered in section Change PWM Frequency.

Change PWM Duty by Software

Setting of the duty is done by first calling dedicated function ledc_set_duty() and then calling ledc_update_duty() to make the change effective. To check the value currently set, there is a corresponding _get_ function ledc_get_duty().

Another way to set the duty, and some other channel parameters as well, is by calling ledc_channel_config() discussed in the previous section.

The range of the duty value entered into functions depends on selected bit number (`` bit_num``) and should be from 0 to (2 ** bit_num) - 1. For example, if selected bit number is 10, then the duty range is from 0 to 1023. This provides the duty resolution of ~0.1%.

Change PWM Duty with Hardware Fading

The LEDC hardware provides the means to gradually fade from one duty value to another. To use this functionality first enable fading with ledc_fade_func_install(). Then configure it by calling one of available fading functions:

Finally start fading with ledc_fade_start().

If not required anymore, fading and associated interrupt may be disabled with ledc_fade_func_uninstall().

Change PWM Frequency

The LEDC API provides several means to change the PWM frequency “on the fly”.

More Control Over PWM

There are couple of lower level timer specific functions, that may be used to provide additional means to change the PWM settings:

The first two functions are called “behind the scenes” by ledc_channel_config() to provide “clean” start up of a timer after is it configured.

Use Interrupts

When configuring a LEDC channel, one of parameters selected within ledc_channel_config_t is ledc_intr_type_t and allows to enable an interrupt on fade completion.

Registration of a handler to service this interrupt is done by calling ledc_isr_register().

LEDC High and Low Speed Mode

Out of the total 8 timers and 16 channels available in the LED PWM Controller, half of them are dedicated to operate in the high speed mode and the other half in the low speed mode. Selection of the low or high speed “capable” timer or the channel is done with parameter ledc_mode_t that is present in applicable function calls.

The advantage of the high speed mode is h/w supported, glitch-free changeover of the timer settings. This means that if the timer settings are modified, the changes will be applied automatically after the next overflow interrupt of the timer. In contrast, when updating the low-speed timer, the change of settings should be specifically triggered by software. The LEDC API is doing it “behind the scenes”, e.g. when ledc_timer_config() or ledc_timer_set() is called.

For additional details regarding speed modes please refer to ESP32 Technical Reference Manual (PDF). Note that support for SLOW_CLOCK mentioned in this manual is not implemented in the LEDC API.

Supported Range of Frequency and Bit Number

The LED PWM Controller is designed primarily to drive LEDs and provides wide resolution of PWM duty settings. The resolution (or granularity) of the PWM duty is determined by the “bit number”. For instance for the PWM frequency at 5 kHz, the maximum bit number is 13 bits. It means that the duty may be set anywhere from 0 to 100% with resolution of ~0.012% (13 ** 2 = 8192 discrete levels of the LED intensity).

The LEDC may be used for providing signals at much higher frequencies to clock other devices, e.g. a digital camera module. In such a case the maximum available frequency is 40 MHz with duty resolution of 1 bit. This means that duty is fixed at 50% and cannot be adjusted.

The API is designed to report an error when trying to set a frequency and a bit number that is out of the range of LEDC’s hardware. For example, an attempt to set the frequency at 20 MHz and the bit number of 3 bits will result in the following error reported on a serial monitor:

E (196) ledc: requested frequency and bit number can not be achieved, try reducing freq_hz or bit_num. div_param=128

In such a case either the bit number or the frequency should be reduced. For example setting the bit number at 2 will resolve this issue and provide possibility to set the duty with 25% steps, i.e. at 25%, 50% or 75%.

The LEDC API will also capture and report an attempt to configure frequency / bit number combination that is below the supported minimum, e.g.:

E (196) ledc: requested frequency and bit depth can not be achieved, try increasing freq_hz or bit_num. div_param=128000000

Setting of the bit number is normally done using ledc_timer_bit_t. This enumeration covers the range from 10 to 15 bits. If a smaller bit number is required (below 10 down to 1), enter the equivalent numeric values directly.

Application Example

The LEDC change duty cycle and fading control example: peripherals/ledc.

API Reference

Functions

esp_err_t ledc_channel_config(const ledc_channel_config_t *ledc_conf)

LEDC channel configuration Configure LEDC channel with the given channel/output gpio_num/interrupt/source timer/frequency(Hz)/LEDC depth.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • ledc_conf: Pointer of LEDC channel configure struct

esp_err_t ledc_timer_config(const ledc_timer_config_t *timer_conf)

LEDC timer configuration Configure LEDC timer with the given source timer/frequency(Hz)/bit_num.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_FAIL Can not find a proper pre-divider number base on the given frequency and the current bit_num.
Parameters
  • timer_conf: Pointer of LEDC timer configure struct

esp_err_t ledc_update_duty(ledc_mode_t speed_mode, ledc_channel_t channel)

LEDC update channel parameters Call this function to activate the LEDC updated parameters. After ledc_set_duty, ledc_set_fade, we need to call this function to update the settings.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode,
  • channel: LEDC channel(0-7), select from ledc_channel_t

esp_err_t ledc_stop(ledc_mode_t speed_mode, ledc_channel_t channel, uint32_t idle_level)

LEDC stop. Disable LEDC output, and set idle level.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • channel: LEDC channel(0-7), select from ledc_channel_t
  • idle_level: Set output idle level after LEDC stops.

esp_err_t ledc_set_freq(ledc_mode_t speed_mode, ledc_timer_t timer_num, uint32_t freq_hz)

LEDC set channel frequency(Hz)

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_FAIL Can not find a proper pre-divider number base on the given frequency and the current bit_num.
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • timer_num: LEDC timer index(0-3), select from ledc_timer_t
  • freq_hz: Set the LEDC frequency

uint32_t ledc_get_freq(ledc_mode_t speed_mode, ledc_timer_t timer_num)

LEDC get channel frequency(Hz)

Return
  • 0 error
  • Others Current LEDC frequency
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • timer_num: LEDC timer index(0-3), select from ledc_timer_t

esp_err_t ledc_set_duty(ledc_mode_t speed_mode, ledc_channel_t channel, uint32_t duty)

LEDC set duty Only after calling ledc_update_duty will the duty update.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • channel: LEDC channel(0-7), select from ledc_channel_t
  • duty: Set the LEDC duty, the duty range is [0, (2**bit_num) - 1]

uint32_t ledc_get_duty(ledc_mode_t speed_mode, ledc_channel_t channel)

LEDC get duty.

Return
  • LEDC_ERR_DUTY if parameter error
  • Others Current LEDC duty
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • channel: LEDC channel(0-7), select from ledc_channel_t

esp_err_t ledc_set_fade(ledc_mode_t speed_mode, ledc_channel_t channel, uint32_t duty, ledc_duty_direction_t gradule_direction, uint32_t step_num, uint32_t duty_cyle_num, uint32_t duty_scale)

LEDC set gradient Set LEDC gradient, After the function calls the ledc_update_duty function, the function can take effect.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Parameter error
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • channel: LEDC channel(0-7), select from ledc_channel_t
  • duty: Set the start of the gradient duty, the duty range is [0, (2**bit_num) - 1]
  • gradule_direction: Set the direction of the gradient
  • step_num: Set the number of the gradient
  • duty_cyle_num: Set how many LEDC tick each time the gradient lasts
  • duty_scale: Set gradient change amplitude

esp_err_t ledc_isr_register(void (*fn)(void *), void *arg, int intr_alloc_flags, ledc_isr_handle_t *handle, )

Register LEDC interrupt handler, the handler is an ISR. The handler will be attached to the same CPU core that this function is running on.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_ARG Function pointer error.
Parameters
  • fn: Interrupt handler function.
  • arg: User-supplied argument passed to the handler function.
  • intr_alloc_flags: Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info.
  • arg: Parameter for handler function
  • handle: Pointer to return handle. If non-NULL, a handle for the interrupt will be returned here.

esp_err_t ledc_timer_set(ledc_mode_t speed_mode, ledc_timer_t timer_sel, uint32_t div_num, uint32_t bit_num, ledc_clk_src_t clk_src)

Configure LEDC settings.

Return
  • (-1) Parameter error
  • Other Current LEDC duty
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • timer_sel: Timer index(0-3), there are 4 timers in LEDC module
  • div_num: Timer clock divide number, the timer clock is divided from the selected clock source
  • bit_num: The count number of one period, counter range is 0 ~ ((2 ** bit_num) - 1)
  • clk_src: Select LEDC source clock.

esp_err_t ledc_timer_rst(ledc_mode_t speed_mode, uint32_t timer_sel)

Reset LEDC timer.

Return
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_OK Success
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • timer_sel: LEDC timer index(0-3), select from ledc_timer_t

esp_err_t ledc_timer_pause(ledc_mode_t speed_mode, uint32_t timer_sel)

Pause LEDC timer counter.

Return
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_OK Success
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • timer_sel: LEDC timer index(0-3), select from ledc_timer_t

esp_err_t ledc_timer_resume(ledc_mode_t speed_mode, uint32_t timer_sel)

Resume LEDC timer.

Return
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_OK Success
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • timer_sel: LEDC timer index(0-3), select from ledc_timer_t

esp_err_t ledc_bind_channel_timer(ledc_mode_t speed_mode, uint32_t channel, uint32_t timer_idx)

Bind LEDC channel with the selected timer.

Return
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_OK Success
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • channel: LEDC channel index(0-7), select from ledc_channel_t
  • timer_idx: LEDC timer index(0-3), select from ledc_timer_t

esp_err_t ledc_set_fade_with_step(ledc_mode_t speed_mode, ledc_channel_t channel, uint32_t target_duty, int scale, int cycle_num)

Set LEDC fade function. Should call ledc_fade_func_install() before calling this function. Call ledc_fade_start() after this to start fading.

Return
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_OK Success
  • ESP_ERR_INVALID_STATE Fade function not installed.
  • ESP_FAIL Fade function init error
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode,
  • channel: LEDC channel index(0-7), select from ledc_channel_t
  • target_duty: Target duty of fading.( 0 - (2 ** bit_num - 1)))
  • scale: Controls the increase or decrease step scale.
  • cycle_num: increase or decrease the duty every cycle_num cycles

esp_err_t ledc_set_fade_with_time(ledc_mode_t speed_mode, ledc_channel_t channel, uint32_t target_duty, int max_fade_time_ms)

Set LEDC fade function, with a limited time. Should call ledc_fade_func_install() before calling this function. Call ledc_fade_start() after this to start fading.

Return
  • ESP_ERR_INVALID_ARG Parameter error
  • ESP_OK Success
  • ESP_ERR_INVALID_STATE Fade function not installed.
  • ESP_FAIL Fade function init error
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode,
  • channel: LEDC channel index(0-7), select from ledc_channel_t
  • target_duty: Target duty of fading.( 0 - (2 ** bit_num - 1)))
  • max_fade_time_ms: The maximum time of the fading ( ms ).

esp_err_t ledc_fade_func_install(int intr_alloc_flags)

Install ledc fade function. This function will occupy interrupt of LEDC module.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_STATE Fade function already installed.
Parameters
  • intr_alloc_flags: Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info.

void ledc_fade_func_uninstall()

Uninstall LEDC fade function.

esp_err_t ledc_fade_start(ledc_mode_t speed_mode, ledc_channel_t channel, ledc_fade_mode_t wait_done)

Start LEDC fading.

Return
  • ESP_OK Success
  • ESP_ERR_INVALID_STATE Fade function not installed.
  • ESP_ERR_INVALID_ARG Parameter error.
Parameters
  • speed_mode: Select the LEDC speed_mode, high-speed mode and low-speed mode
  • channel: LEDC channel number
  • wait_done: Whether to block until fading done.

Structures

struct ledc_channel_config_t

Configuration parameters of LEDC channel for ledc_channel_config function.

Public Members

int gpio_num

the LEDC output gpio_num, if you want to use gpio16, gpio_num = 16

ledc_mode_t speed_mode

LEDC speed speed_mode, high-speed mode or low-speed mode

ledc_channel_t channel

LEDC channel(0 - 7)

ledc_intr_type_t intr_type

configure interrupt, Fade interrupt enable or Fade interrupt disable

ledc_timer_t timer_sel

Select the timer source of channel (0 - 3)

uint32_t duty

LEDC channel duty, the duty range is [0, (2**bit_num) - 1],

struct ledc_timer_config_t

Configuration parameters of LEDC Timer timer for ledc_timer_config function.

Public Members

ledc_mode_t speed_mode

LEDC speed speed_mode, high-speed mode or low-speed mode

ledc_timer_bit_t bit_num

LEDC channel duty depth

ledc_timer_t timer_num

The timer source of channel (0 - 3)

uint32_t freq_hz

LEDC timer frequency(Hz)

Macros

LEDC_APB_CLK_HZ
LEDC_REF_CLK_HZ
LEDC_ERR_DUTY

Type Definitions

typedef intr_handle_t ledc_isr_handle_t

Enumerations

enum ledc_mode_t

Values:

LEDC_HIGH_SPEED_MODE = 0

LEDC high speed speed_mode

LEDC_LOW_SPEED_MODE

LEDC low speed speed_mode

LEDC_SPEED_MODE_MAX

LEDC speed limit

enum ledc_intr_type_t

Values:

LEDC_INTR_DISABLE = 0

Disable LEDC interrupt

LEDC_INTR_FADE_END

Enable LEDC interrupt

enum ledc_duty_direction_t

Values:

LEDC_DUTY_DIR_DECREASE = 0

LEDC duty decrease direction

LEDC_DUTY_DIR_INCREASE = 1

LEDC duty increase direction

enum ledc_clk_src_t

Values:

LEDC_REF_TICK = 0

LEDC timer clock divided from reference tick(1Mhz)

LEDC_APB_CLK

LEDC timer clock divided from APB clock(80Mhz)

enum ledc_timer_t

Values:

LEDC_TIMER_0 = 0

LEDC source timer TIMER0

LEDC_TIMER_1

LEDC source timer TIMER1

LEDC_TIMER_2

LEDC source timer TIMER2

LEDC_TIMER_3

LEDC source timer TIMER3

enum ledc_channel_t

Values:

LEDC_CHANNEL_0 = 0

LEDC channel 0

LEDC_CHANNEL_1

LEDC channel 1

LEDC_CHANNEL_2

LEDC channel 2

LEDC_CHANNEL_3

LEDC channel 3

LEDC_CHANNEL_4

LEDC channel 4

LEDC_CHANNEL_5

LEDC channel 5

LEDC_CHANNEL_6

LEDC channel 6

LEDC_CHANNEL_7

LEDC channel 7

LEDC_CHANNEL_MAX
enum ledc_timer_bit_t

Values:

LEDC_TIMER_10_BIT = 10

LEDC PWM depth 10Bit

LEDC_TIMER_11_BIT = 11

LEDC PWM depth 11Bit

LEDC_TIMER_12_BIT = 12

LEDC PWM depth 12Bit

LEDC_TIMER_13_BIT = 13

LEDC PWM depth 13Bit

LEDC_TIMER_14_BIT = 14

LEDC PWM depth 14Bit

LEDC_TIMER_15_BIT = 15

LEDC PWM depth 15Bit

enum ledc_fade_mode_t

Values:

LEDC_FADE_NO_WAIT = 0

LEDC fade function will return immediately

LEDC_FADE_WAIT_DONE

LEDC fade function will block until fading to the target duty

LEDC_FADE_MAX