Pulse Counter (PCNT)

Introduction

The PCNT (Pulse Counter) module is designed to count the number of rising and/or falling edges of input signals. The ESP32 contains multiple pulse counter units in the module. 1 Each unit is in effect an independent counter with multiple channels, where each channel can increment/decrement the counter on a rising/falling edge. Furthermore, each channel can be configured separately.

PCNT channels can react to signals of edge type and level type, however for simple applications, detecting the edge signal is usually sufficient. PCNT channels can be configured react to both pulse edges (i.e., rising and falling edge), and can be configured to increase, decrease or do nothing to the unit's counter on each edge. The level signal is the so-called control signal, which is used to control the counting mode of the edge signals that are attached to the same channel. By combining the usage of both edge and level signals, a PCNT unit can act as a quadrature decoder.

Besides that, PCNT unit is equipped with a separate glitch filter, which is helpful to remove noise from the signal.

Typically, a PCNT module can be used in scenarios like:

  • Calculate periodic signal's frequency by counting the pulse numbers within a time slice

  • Decode quadrature signals into speed and direction

Functional Overview

Description of the PCNT functionality is divided into the following sections:

  • Resource Allocation - covers how to allocate PCNT units and channels with properly set of configurations. It also covers how to recycle the resources when they finished working.

  • Set Up Channel Actions - covers how to configure the PCNT channel to behave on different signal edges and levels.

  • Watch Points - describes how to configure PCNT watch points (i.e., tell PCNT unit to trigger an event when the count reaches a certain value).

  • Register Event Callbacks - describes how to hook your specific code to the watch point event callback function.

  • Set Glitch Filter - describes how to enable and set the timing parameters for the internal glitch filter.

  • Enable and Disable Unit - describes how to enable and disable the PCNT unit.

  • Unit IO Control - describes IO control functions of PCNT unit, like enable glitch filter, start and stop unit, get and clear count value.

  • Power Management - describes what functionality will prevent the chip from going into low power mode.

  • IRAM Safe - describes tips on how to make the PCNT interrupt and IO control functions work better along with a disabled cache.

  • Thread Safety - lists which APIs are guaranteed to be thread safe by the driver.

  • Kconfig Options - lists the supported Kconfig options that can be used to make a different effect on driver behavior.

Resource Allocation

The PCNT unit and channel are represented by pcnt_unit_handle_t and pcnt_channel_handle_t respectively. All available units and channels are maintained by the driver in a resource pool, so you do not need to know the exact underlying instance ID.

Install PCNT Unit

To install a PCNT unit, there is a configuration structure that needs to be given in advance: pcnt_unit_config_t:

Note

Since all PCNT units share the same interrupt source, when installing multiple PCNT units make sure that the interrupt priority pcnt_unit_config_t::intr_priority is the same for each unit.

Unit allocation and initialization is done by calling a function pcnt_new_unit() with pcnt_unit_config_t as an input parameter. The function will return a PCNT unit handle only when it runs correctly. Specifically, when there are no more free PCNT units in the pool (i.e., unit resources have been used up), then this function will return ESP_ERR_NOT_FOUND error. The total number of available PCNT units is recorded by SOC_PCNT_UNITS_PER_GROUP for reference.

If a previously created PCNT unit is no longer needed, it is recommended to recycle the resource by calling pcnt_del_unit(). Which in return allows the underlying unit hardware to be used for other purposes. Before deleting a PCNT unit, one should ensure the following prerequisites:

  • The unit is in the init state, in other words, the unit is either disabled by pcnt_unit_disable() or not enabled yet.

  • The attached PCNT channels are all removed by pcnt_del_channel().

#define EXAMPLE_PCNT_HIGH_LIMIT 100
#define EXAMPLE_PCNT_LOW_LIMIT  -100

pcnt_unit_config_t unit_config = {
    .high_limit = EXAMPLE_PCNT_HIGH_LIMIT,
    .low_limit = EXAMPLE_PCNT_LOW_LIMIT,
};
pcnt_unit_handle_t pcnt_unit = NULL;
ESP_ERROR_CHECK(pcnt_new_unit(&unit_config, &pcnt_unit));

Install PCNT Channel

To install a PCNT channel, you must initialize a pcnt_chan_config_t structure in advance, and then call pcnt_new_channel(). The configuration fields of the pcnt_chan_config_t structure are described below:

Channel allocating and initialization is done by calling a function pcnt_new_channel() with the above pcnt_chan_config_t as an input parameter plus a PCNT unit handle returned from pcnt_new_unit(). This function will return a PCNT channel handle if it runs correctly. Specifically, when there are no more free PCNT channel within the unit (i.e., channel resources have been used up), then this function will return ESP_ERR_NOT_FOUND error. The total number of available PCNT channels within the unit is recorded by SOC_PCNT_CHANNELS_PER_UNIT for reference. Note that, when install a PCNT channel for a specific unit, one should ensure the unit is in the init state, otherwise this function will return ESP_ERR_INVALID_STATE error.

If a previously created PCNT channel is no longer needed, it is recommended to recycle the resources by calling pcnt_del_channel(). Which in return allows the underlying channel hardware to be used for other purposes.

#define EXAMPLE_CHAN_GPIO_A 0
#define EXAMPLE_CHAN_GPIO_B 2

pcnt_chan_config_t chan_config = {
    .edge_gpio_num = EXAMPLE_CHAN_GPIO_A,
    .level_gpio_num = EXAMPLE_CHAN_GPIO_B,
};
pcnt_channel_handle_t pcnt_chan = NULL;
ESP_ERROR_CHECK(pcnt_new_channel(pcnt_unit, &chan_config, &pcnt_chan));

Note

In PCNT, the GPIOs involved can be reconfigured for pull-up or pull-down after initializing PCNT using functions such as gpio_pullup_en() and gpio_pullup_dis().

Set Up Channel Actions

The PCNT will increase/decrease/hold its internal count value when the input pulse signal toggles. You can set different actions for edge signal and/or level signal.

// decrease the counter on rising edge, increase the counter on falling edge
ESP_ERROR_CHECK(pcnt_channel_set_edge_action(pcnt_chan, PCNT_CHANNEL_EDGE_ACTION_DECREASE, PCNT_CHANNEL_EDGE_ACTION_INCREASE));
// keep the counting mode when the control signal is high level, and reverse the counting mode when the control signal is low level
ESP_ERROR_CHECK(pcnt_channel_set_level_action(pcnt_chan, PCNT_CHANNEL_LEVEL_ACTION_KEEP, PCNT_CHANNEL_LEVEL_ACTION_INVERSE));

Watch Points

Each PCNT unit can be configured to watch several different values that you are interested in. The value to be watched is also called Watch Point. The watch point itself can not exceed the range set in pcnt_unit_config_t by pcnt_unit_config_t::low_limit and pcnt_unit_config_t::high_limit. When the counter reaches either watch point, a watch event will be triggered and notify you by interrupt if any watch event callback has ever registered in pcnt_unit_register_event_callbacks(). See Register Event Callbacks for how to register event callbacks.

The watch point can be added and removed by pcnt_unit_add_watch_point() and pcnt_unit_remove_watch_point(). The commonly-used watch points are: zero cross, maximum/minimum count and other threshold values. The number of available watch point is limited, pcnt_unit_add_watch_point() will return error ESP_ERR_NOT_FOUND if it can not find any free hardware resource to save the watch point. You can not add the same watch point for multiple times, otherwise it will return error ESP_ERR_INVALID_STATE.

It is recommended to remove the unused watch point by pcnt_unit_remove_watch_point() to recycle the watch point resources.

// add zero across watch point
ESP_ERROR_CHECK(pcnt_unit_add_watch_point(pcnt_unit, 0));
// add high limit watch point
ESP_ERROR_CHECK(pcnt_unit_add_watch_point(pcnt_unit, EXAMPLE_PCNT_HIGH_LIMIT));

Note

Due to the hardware limitation, after adding a watch point, you should call pcnt_unit_clear_count() to make it take effect.

Register Event Callbacks

When PCNT unit reaches any enabled watch point, specific event will be generated and notify the CPU by interrupt. If you have some function that want to get executed when event happens, you should hook your function to the interrupt service routine by calling pcnt_unit_register_event_callbacks(). All supported event callbacks are listed in the pcnt_event_callbacks_t:

  • pcnt_event_callbacks_t::on_reach sets a callback function for watch point event. As this function is called within the ISR context, you must ensure that the function does not attempt to block (e.g., by making sure that only FreeRTOS APIs with ISR suffix are called from within the function). The function prototype is declared in pcnt_watch_cb_t.

You can save their own context to pcnt_unit_register_event_callbacks() as well, via the parameter user_ctx. This user data will be directly passed to the callback functions.

In the callback function, the driver will fill in the event data of specific event. For example, the watch point event or watch step event data is declared as pcnt_watch_event_data_t:

Registering callback function results in lazy installation of interrupt service, thus this function should only be called before the unit is enabled by pcnt_unit_enable(). Otherwise, it can return ESP_ERR_INVALID_STATE error.

static bool example_pcnt_on_reach(pcnt_unit_handle_t unit, const pcnt_watch_event_data_t *edata, void *user_ctx)
{
    BaseType_t high_task_wakeup;
    QueueHandle_t queue = (QueueHandle_t)user_ctx;
    // send watch point to queue, from this interrupt callback
    xQueueSendFromISR(queue, &(edata->watch_point_value), &high_task_wakeup);
    // return whether a high priority task has been waken up by this function
    return (high_task_wakeup == pdTRUE);
}

pcnt_event_callbacks_t cbs = {
    .on_reach = example_pcnt_on_reach,
};
QueueHandle_t queue = xQueueCreate(10, sizeof(int));
ESP_ERROR_CHECK(pcnt_unit_register_event_callbacks(pcnt_unit, &cbs, queue));

Set Glitch Filter

The PCNT unit features filters to ignore possible short glitches in the signals. The parameters that can be configured for the glitch filter are listed in pcnt_glitch_filter_config_t:

  • pcnt_glitch_filter_config_t::max_glitch_ns sets the maximum glitch width, in nano seconds. If a signal pulse's width is smaller than this value, then it will be treated as noise and will not increase/decrease the internal counter.

You can enable the glitch filter for PCNT unit by calling pcnt_unit_set_glitch_filter() with the filter configuration provided above. Particularly, you can disable the glitch filter later by calling pcnt_unit_set_glitch_filter() with a NULL filter configuration.

This function should be called when the unit is in the init state. Otherwise, it will return ESP_ERR_INVALID_STATE error.

Note

The glitch filter operates using the APB clock. To ensure the counter does not miss any pulses, the maximum glitch width should be longer than one APB_CLK cycle (typically 12.5 ns if APB is 80 MHz). Since the APB frequency can change with Dynamic Frequency Scaling (DFS), the filter may not function as expected in such cases. Therefore, the driver installs a power management lock for each PCNT unit. For more details on the power management strategy used in the PCNT driver, please refer to Power Management.

pcnt_glitch_filter_config_t filter_config = {
    .max_glitch_ns = 1000,
};
ESP_ERROR_CHECK(pcnt_unit_set_glitch_filter(pcnt_unit, &filter_config));

Enable and Disable Unit

Before doing IO control to the PCNT unit, you need to enable it first, by calling pcnt_unit_enable(). Internally, this function:

  • switches the PCNT driver state from init to enable.

  • enables the interrupt service if it has been lazy installed in pcnt_unit_register_event_callbacks().

  • acquires a proper power management lock if it has been installed. See also Power Management for more information.

On the contrary, calling pcnt_unit_disable() will do the opposite, that is, put the PCNT driver back to the init state, disable the interrupts service and release the power management lock.

Unit IO Control

Start/Stop and Clear

Calling pcnt_unit_start() makes the PCNT unit start to work, increase or decrease counter according to pulse signals. On the contrary, calling pcnt_unit_stop() will stop the PCNT unit but retain current count value. Instead, clearing counter can only be done by calling pcnt_unit_clear_count().

Note, pcnt_unit_start() and pcnt_unit_stop() should be called when the unit has been enabled by pcnt_unit_enable(). Otherwise, it will return ESP_ERR_INVALID_STATE error.

Get Count Value

You can read current count value at any time by calling pcnt_unit_get_count(). The returned count value is a signed integer, where the sign can be used to reflect the direction.

int pulse_count = 0;
ESP_ERROR_CHECK(pcnt_unit_get_count(pcnt_unit, &pulse_count));

Compensate Overflow Loss

The internal hardware counter will be cleared to zero automatically when it reaches high or low limit. If you want to compensate for that count loss and extend the counter's bit-width, you can:

  1. Enable pcnt_unit_config_t::accum_count when installing the PCNT unit.

  2. Add the high/low limit as the Watch Points.

  3. Now, the returned count value from the pcnt_unit_get_count() function not only reflects the hardware's count value, but also accumulates the high/low overflow loss to it.

Note

pcnt_unit_clear_count() resets the accumulated count value as well.

Power Management

When power management is enabled (i.e., CONFIG_PM_ENABLE is on), the system adjusts the APB frequency before entering light sleep, which can cause the PCNT glitch filter to misinterpret valid signals as noise.

To prevent this, the driver can acquire a power management lock of type ESP_PM_APB_FREQ_MAX, ensuring the APB frequency remains constant. This lock is acquired when the PCNT unit is enabled via pcnt_unit_enable() and released when the unit is disabled via pcnt_unit_disable().

IRAM Safe

By default, the PCNT interrupt will be deferred when the Cache is disabled for reasons like writing/erasing Flash. Thus the alarm interrupt will not get executed in time, which is not expected in a real-time application.

There is a Kconfig option CONFIG_PCNT_ISR_IRAM_SAFE that:

  1. Enables the interrupt being serviced even when cache is disabled

  2. Places all functions that used by the ISR into IRAM 2

  3. Places driver object into DRAM (in case it is mapped to PSRAM by accident)

This allows the interrupt to run while the cache is disabled but comes at the cost of increased IRAM consumption.

There is another Kconfig option CONFIG_PCNT_CTRL_FUNC_IN_IRAM that can put commonly used IO control functions into IRAM as well. So that these functions can also be executable when the cache is disabled. These IO control functions are as follows:

Thread Safety

The factory functions pcnt_new_unit() and pcnt_new_channel() are guaranteed to be thread safe by the driver, which means, you can call them from different RTOS tasks without protection by extra locks.

The following functions are allowed to run under ISR context, the driver uses a critical section to prevent them being called concurrently in both task and ISR.

Other functions that take the pcnt_unit_handle_t and pcnt_channel_handle_t as the first positional parameter, are not treated as thread safe. This means you should avoid calling them from multiple tasks.

Kconfig Options

Application Examples

  • peripherals/pcnt/rotary_encoder demonstrates how to use the PCNT peripheral to decode the differential signals generated from a common rotary encoder, EC11, and how to configure the rotary encoder to wake the system from light-sleep.

API Reference

Header File

  • components/esp_driver_pcnt/include/driver/pulse_cnt.h

  • This header file can be included with:

    #include "driver/pulse_cnt.h"

  • This header file is a part of the API provided by the esp_driver_pcnt component. To declare that your component depends on esp_driver_pcnt, add the following to your CMakeLists.txt:

    REQUIRES esp_driver_pcnt

    or

    PRIV_REQUIRES esp_driver_pcnt

Functions

esp_err_t pcnt_new_unit(const pcnt_unit_config_t *config, pcnt_unit_handle_t *ret_unit)

Create a new PCNT unit, and return the handle.

Note

The newly created PCNT unit is put in the init state.

Parameters

  • config -- [in] PCNT unit configuration

  • ret_unit -- [out] Returned PCNT unit handle

Returns

  • ESP_OK: Create PCNT unit successfully

  • ESP_ERR_INVALID_ARG: Create PCNT unit failed because of invalid argument (e.g. high/low limit value out of the range)

  • ESP_ERR_NO_MEM: Create PCNT unit failed because out of memory

  • ESP_ERR_NOT_FOUND: Create PCNT unit failed because all PCNT units are used up and no more free one

  • ESP_FAIL: Create PCNT unit failed because of other error

esp_err_t pcnt_del_unit(pcnt_unit_handle_t unit)

Delete the PCNT unit handle.

Note

A PCNT unit can't be in the enable state when this function is invoked. See also pcnt_unit_disable() for how to disable a unit.

Parameters

unit -- [in] PCNT unit handle created by pcnt_new_unit()

Returns

  • ESP_OK: Delete the PCNT unit successfully

  • ESP_ERR_INVALID_ARG: Delete the PCNT unit failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Delete the PCNT unit failed because the unit is not in init state or some PCNT channel is still in working

  • ESP_FAIL: Delete the PCNT unit failed because of other error

esp_err_t pcnt_unit_set_glitch_filter(pcnt_unit_handle_t unit, const pcnt_glitch_filter_config_t *config)

Set glitch filter for PCNT unit.

Note

The glitch filter module is clocked from APB, and APB frequency can be changed during DFS, which in return make the filter out of action. So this function will lazy-install a PM lock internally when the power management is enabled. With this lock, the APB frequency won't be changed. The PM lock can be uninstalled in pcnt_del_unit().

Note

This function should be called when the PCNT unit is in the init state (i.e. before calling pcnt_unit_enable())

Parameters

  • unit -- [in] PCNT unit handle created by pcnt_new_unit()

  • config -- [in] PCNT filter configuration, set config to NULL means disabling the filter function

Returns

  • ESP_OK: Set glitch filter successfully

  • ESP_ERR_INVALID_ARG: Set glitch filter failed because of invalid argument (e.g. glitch width is too big)

  • ESP_ERR_INVALID_STATE: Set glitch filter failed because the unit is not in the init state

  • ESP_FAIL: Set glitch filter failed because of other error

esp_err_t pcnt_unit_enable(pcnt_unit_handle_t unit)

Enable the PCNT unit.

Note

This function will transit the unit state from init to enable.

Note

This function will enable the interrupt service, if it's lazy installed in pcnt_unit_register_event_callbacks().

Note

This function will acquire the PM lock if it's lazy installed in pcnt_unit_set_glitch_filter().

Note

Enable a PCNT unit doesn't mean to start it. See also pcnt_unit_start() for how to start the PCNT counter.

Parameters

unit -- [in] PCNT unit handle created by pcnt_new_unit()

Returns

  • ESP_OK: Enable PCNT unit successfully

  • ESP_ERR_INVALID_ARG: Enable PCNT unit failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Enable PCNT unit failed because the unit is already enabled

  • ESP_FAIL: Enable PCNT unit failed because of other error

esp_err_t pcnt_unit_disable(pcnt_unit_handle_t unit)

Disable the PCNT unit.

Note

This function will do the opposite work to the pcnt_unit_enable()

Note

Disable a PCNT unit doesn't mean to stop it. See also pcnt_unit_stop() for how to stop the PCNT counter.

Parameters

unit -- [in] PCNT unit handle created by pcnt_new_unit()

Returns

  • ESP_OK: Disable PCNT unit successfully

  • ESP_ERR_INVALID_ARG: Disable PCNT unit failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Disable PCNT unit failed because the unit is not enabled yet

  • ESP_FAIL: Disable PCNT unit failed because of other error

esp_err_t pcnt_unit_start(pcnt_unit_handle_t unit)

Start the PCNT unit, the counter will start to count according to the edge and/or level input signals.

Note

This function should be called when the unit is in the enable state (i.e. after calling pcnt_unit_enable())

Note

This function is allowed to run within ISR context

Note

This function will be placed into IRAM if CONFIG_PCNT_CTRL_FUNC_IN_IRAM is on, so that it's allowed to be executed when Cache is disabled

Parameters

unit -- [in] PCNT unit handle created by pcnt_new_unit()

Returns

  • ESP_OK: Start PCNT unit successfully

  • ESP_ERR_INVALID_ARG: Start PCNT unit failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Start PCNT unit failed because the unit is not enabled yet

  • ESP_FAIL: Start PCNT unit failed because of other error

esp_err_t pcnt_unit_stop(pcnt_unit_handle_t unit)

Stop PCNT from counting.

Note

This function should be called when the unit is in the enable state (i.e. after calling pcnt_unit_enable())

Note

The stop operation won't clear the counter. Also see pcnt_unit_clear_count() for how to clear pulse count value.

Note

This function is allowed to run within ISR context

Note

This function will be placed into IRAM if CONFIG_PCNT_CTRL_FUNC_IN_IRAM, so that it is allowed to be executed when Cache is disabled

Parameters

unit -- [in] PCNT unit handle created by pcnt_new_unit()

Returns

  • ESP_OK: Stop PCNT unit successfully

  • ESP_ERR_INVALID_ARG: Stop PCNT unit failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Stop PCNT unit failed because the unit is not enabled yet

  • ESP_FAIL: Stop PCNT unit failed because of other error

esp_err_t pcnt_unit_clear_count(pcnt_unit_handle_t unit)

Clear PCNT pulse count value to zero.

Note

It's recommended to call this function after adding a watch point by pcnt_unit_add_watch_point(), so that the newly added watch point is effective immediately.

Note

This function is allowed to run within ISR context

Note

This function will be placed into IRAM if CONFIG_PCNT_CTRL_FUNC_IN_IRAM, so that it's allowed to be executed when Cache is disabled

Parameters

unit -- [in] PCNT unit handle created by pcnt_new_unit()

Returns

  • ESP_OK: Clear PCNT pulse count successfully

  • ESP_ERR_INVALID_ARG: Clear PCNT pulse count failed because of invalid argument

  • ESP_FAIL: Clear PCNT pulse count failed because of other error

esp_err_t pcnt_unit_get_count(pcnt_unit_handle_t unit, int *value)

Get PCNT count value.

Note

This function is allowed to run within ISR context

Note

This function will be placed into IRAM if CONFIG_PCNT_CTRL_FUNC_IN_IRAM, so that it's allowed to be executed when Cache is disabled

Parameters

  • unit -- [in] PCNT unit handle created by pcnt_new_unit()

  • value -- [out] Returned count value

Returns

  • ESP_OK: Get PCNT pulse count successfully

  • ESP_ERR_INVALID_ARG: Get PCNT pulse count failed because of invalid argument

  • ESP_FAIL: Get PCNT pulse count failed because of other error

esp_err_t pcnt_unit_register_event_callbacks(pcnt_unit_handle_t unit, const pcnt_event_callbacks_t *cbs, void *user_data)

Set event callbacks for PCNT unit.

Note

User registered callbacks are expected to be runnable within ISR context

Note

The first call to this function needs to be before the call to pcnt_unit_enable

Note

User can deregister a previously registered callback by calling this function and setting the callback member in the cbs structure to NULL.

Parameters

  • unit -- [in] PCNT unit handle created by pcnt_new_unit()

  • cbs -- [in] Group of callback functions

  • user_data -- [in] User data, which will be passed to callback functions directly

Returns

  • ESP_OK: Set event callbacks successfully

  • ESP_ERR_INVALID_ARG: Set event callbacks failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Set event callbacks failed because the unit is not in init state

  • ESP_FAIL: Set event callbacks failed because of other error

esp_err_t pcnt_unit_add_watch_point(pcnt_unit_handle_t unit, int watch_point)

Add a watch point for PCNT unit, PCNT will generate an event when the counter value reaches the watch point value.

Parameters

  • unit -- [in] PCNT unit handle created by pcnt_new_unit()

  • watch_point -- [in] Value to be watched

Returns

  • ESP_OK: Add watch point successfully

  • ESP_ERR_INVALID_ARG: Add watch point failed because of invalid argument (e.g. the value to be watched is out of the limitation set in pcnt_unit_config_t)

  • ESP_ERR_INVALID_STATE: Add watch point failed because the same watch point has already been added

  • ESP_ERR_NOT_FOUND: Add watch point failed because no more hardware watch point can be configured

  • ESP_FAIL: Add watch point failed because of other error

esp_err_t pcnt_unit_remove_watch_point(pcnt_unit_handle_t unit, int watch_point)

Remove a watch point for PCNT unit.

Parameters

  • unit -- [in] PCNT unit handle created by pcnt_new_unit()

  • watch_point -- [in] Watch point value

Returns

  • ESP_OK: Remove watch point successfully

  • ESP_ERR_INVALID_ARG: Remove watch point failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Remove watch point failed because the watch point was not added by pcnt_unit_add_watch_point() yet

  • ESP_FAIL: Remove watch point failed because of other error

esp_err_t pcnt_unit_add_watch_step(pcnt_unit_handle_t unit, int step_interval)

Add a step notify for PCNT unit, PCNT will generate an event when the incremental(can be positive or negative) of counter value reaches the step interval.

Parameters

  • unit -- [in] PCNT unit handle created by pcnt_new_unit()

  • step_interval -- [in] PCNT step notify interval value

Returns

  • ESP_OK: Add step notify successfully

  • ESP_ERR_INVALID_ARG: Add step notify failed because of invalid argument (e.g. the value incremental to be watched is out of the limitation set in pcnt_unit_config_t)

  • ESP_ERR_INVALID_STATE: Add step notify failed because the step notify has already been added

  • ESP_FAIL: Add step notify failed because of other error

esp_err_t pcnt_unit_remove_watch_step(pcnt_unit_handle_t unit)

Remove a step notify for PCNT unit.

Parameters

unit -- [in] PCNT unit handle created by pcnt_new_unit()

Returns

  • ESP_OK: Remove step notify successfully

  • ESP_ERR_INVALID_ARG: Remove step notify failed because of invalid argument

  • ESP_ERR_INVALID_STATE: Remove step notify failed because the step notify was not added by pcnt_unit_add_watch_step() yet

  • ESP_FAIL: Remove step notify failed because of other error

esp_err_t pcnt_new_channel(pcnt_unit_handle_t unit, const pcnt_chan_config_t *config, pcnt_channel_handle_t *ret_chan)

Create PCNT channel for specific unit, each PCNT has several channels associated with it.

Note

This function should be called when the unit is in init state (i.e. before calling pcnt_unit_enable())

Parameters

  • unit -- [in] PCNT unit handle created by pcnt_new_unit()

  • config -- [in] PCNT channel configuration

  • ret_chan -- [out] Returned channel handle

Returns

  • ESP_OK: Create PCNT channel successfully

  • ESP_ERR_INVALID_ARG: Create PCNT channel failed because of invalid argument

  • ESP_ERR_NO_MEM: Create PCNT channel failed because of insufficient memory

  • ESP_ERR_NOT_FOUND: Create PCNT channel failed because all PCNT channels are used up and no more free one

  • ESP_ERR_INVALID_STATE: Create PCNT channel failed because the unit is not in the init state

  • ESP_FAIL: Create PCNT channel failed because of other error

esp_err_t pcnt_del_channel(pcnt_channel_handle_t chan)

Delete the PCNT channel.

Parameters

chan -- [in] PCNT channel handle created by pcnt_new_channel()

Returns

  • ESP_OK: Delete the PCNT channel successfully

  • ESP_ERR_INVALID_ARG: Delete the PCNT channel failed because of invalid argument

  • ESP_FAIL: Delete the PCNT channel failed because of other error

esp_err_t pcnt_channel_set_edge_action(pcnt_channel_handle_t chan, pcnt_channel_edge_action_t pos_act, pcnt_channel_edge_action_t neg_act)

Set channel actions when edge signal changes (e.g. falling or rising edge occurred). The edge signal is input from the edge_gpio_num configured in pcnt_chan_config_t. We use these actions to control when and how to change the counter value.

Parameters

  • chan -- [in] PCNT channel handle created by pcnt_new_channel()

  • pos_act -- [in] Action on posedge signal

  • neg_act -- [in] Action on negedge signal

Returns

  • ESP_OK: Set edge action for PCNT channel successfully

  • ESP_ERR_INVALID_ARG: Set edge action for PCNT channel failed because of invalid argument

  • ESP_FAIL: Set edge action for PCNT channel failed because of other error

esp_err_t pcnt_channel_set_level_action(pcnt_channel_handle_t chan, pcnt_channel_level_action_t high_act, pcnt_channel_level_action_t low_act)

Set channel actions when level signal changes (e.g. signal level goes from high to low). The level signal is input from the level_gpio_num configured in pcnt_chan_config_t. We use these actions to control when and how to change the counting mode.

Parameters

  • chan -- [in] PCNT channel handle created by pcnt_new_channel()

  • high_act -- [in] Action on high level signal

  • low_act -- [in] Action on low level signal

Returns

  • ESP_OK: Set level action for PCNT channel successfully

  • ESP_ERR_INVALID_ARG: Set level action for PCNT channel failed because of invalid argument

  • ESP_FAIL: Set level action for PCNT channel failed because of other error

Structures

struct pcnt_watch_event_data_t

PCNT watch event data.

Public Members

int watch_point_value

Watch point value that triggered the event

pcnt_unit_zero_cross_mode_t zero_cross_mode

Zero cross mode

struct pcnt_event_callbacks_t

Group of supported PCNT callbacks.

Note

The callbacks are all running under ISR environment

Note

When CONFIG_PCNT_ISR_IRAM_SAFE is enabled, the callback itself and functions callbed by it should be placed in IRAM.

Public Members

pcnt_watch_cb_t on_reach

Called when PCNT unit counter reaches any watch point or step notify

struct pcnt_unit_config_t

PCNT unit configuration.

Public Members

int low_limit

Low limitation of the count unit, should be lower than 0

int high_limit

High limitation of the count unit, should be higher than 0

int intr_priority

PCNT interrupt priority, if set to 0, the driver will try to allocate an interrupt with a relative low priority (1,2,3)

uint32_t accum_count

Whether to accumulate the count value when overflows at the high/low limit

struct pcnt_unit_config_t::[anonymous] flags

Extra flags

struct pcnt_chan_config_t

PCNT channel configuration.

Public Members

int edge_gpio_num

GPIO number used by the edge signal, input mode with pull up enabled. Set to -1 if unused

int level_gpio_num

GPIO number used by the level signal, input mode with pull up enabled. Set to -1 if unused

uint32_t invert_edge_input

Invert the input edge signal

uint32_t invert_level_input

Invert the input level signal

uint32_t virt_edge_io_level

Virtual edge IO level, 0: low, 1: high. Only valid when edge_gpio_num is set to -1

uint32_t virt_level_io_level

Virtual level IO level, 0: low, 1: high. Only valid when level_gpio_num is set to -1

uint32_t io_loop_back

For debug/test, the signal output from the GPIO will be fed to the input path as well. Note that this flag is deprecated, will be removed in IDF v6.0. Instead, you can configure the output mode by calling gpio_config() first, and then do PCNT channel configuration. Necessary configurations for the IO to be used as the PCNT input will be appended.

struct pcnt_chan_config_t::[anonymous] flags

Channel config flags

struct pcnt_glitch_filter_config_t

PCNT glitch filter configuration.

Public Members

uint32_t max_glitch_ns

Pulse width smaller than this threshold will be treated as glitch and ignored, in the unit of ns

Type Definitions

typedef struct pcnt_unit_t *pcnt_unit_handle_t

Type of PCNT unit handle.

typedef struct pcnt_chan_t *pcnt_channel_handle_t

Type of PCNT channel handle.

typedef bool (*pcnt_watch_cb_t)(pcnt_unit_handle_t unit, const pcnt_watch_event_data_t *edata, void *user_ctx)

PCNT watch event callback prototype.

Note

The callback function is invoked from an ISR context, so it should meet the restrictions of not calling any blocking APIs when implementing the callback. e.g. must use ISR version of FreeRTOS APIs.

Param unit

[in] PCNT unit handle

Param edata

[in] PCNT event data, fed by the driver

Param user_ctx

[in] User data, passed from pcnt_unit_register_event_callbacks()

Return

Whether a high priority task has been woken up by this function

Header File

Enumerations

enum pcnt_channel_level_action_t

PCNT channel action on control level.

Values:

enumerator PCNT_CHANNEL_LEVEL_ACTION_KEEP

Keep current count mode

enumerator PCNT_CHANNEL_LEVEL_ACTION_INVERSE

Invert current count mode (increase -> decrease, decrease -> increase)

enumerator PCNT_CHANNEL_LEVEL_ACTION_HOLD

Hold current count value

enum pcnt_channel_edge_action_t

PCNT channel action on signal edge.

Values:

enumerator PCNT_CHANNEL_EDGE_ACTION_HOLD

Hold current count value

enumerator PCNT_CHANNEL_EDGE_ACTION_INCREASE

Increase count value

enumerator PCNT_CHANNEL_EDGE_ACTION_DECREASE

Decrease count value

enum pcnt_unit_zero_cross_mode_t

PCNT unit zero cross mode.

Values:

enumerator PCNT_UNIT_ZERO_CROSS_POS_ZERO

start from positive value, end to zero, i.e. +N->0

enumerator PCNT_UNIT_ZERO_CROSS_NEG_ZERO

start from negative value, end to zero, i.e. -N->0

enumerator PCNT_UNIT_ZERO_CROSS_NEG_POS

start from negative value, end to positive value, i.e. -N->+M

enumerator PCNT_UNIT_ZERO_CROSS_POS_NEG

start from positive value, end to negative value, i.e. +N->-M

enumerator PCNT_UNIT_ZERO_CROSS_INVALID

invalid zero cross mode

1

Different ESP chip series might have different number of PCNT units and channels. Please refer to the [TRM] for details. The driver does not forbid you from applying for more PCNT units and channels, but it returns error when all available hardware resources are used up. Please always check the return value when doing resource allocation (e.g., pcnt_new_unit()).

2

pcnt_event_callbacks_t::on_reach callback and the functions invoked by itself should also be placed in IRAM, you need to take care of them by themselves.

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