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:

pcnt_unit_config_t::low_limit and pcnt_unit_config_t::high_limit specify the range for the internal hardware counter. The counter will reset to zero automatically when it crosses either the high or low limit.
pcnt_unit_config_t::accum_count sets whether to create an internal accumulator for the counter. This is helpful when you want to extend the counter's width, which by default is 16 bit at most, defined in the hardware. See also Compensate Overflow Loss for how to use this feature to compensate the overflow loss.
pcnt_unit_config_t::intr_priority sets the priority of the interrupt. If it is set to 0, the driver will allocate an interrupt with a default priority. Otherwise, the driver will use the given priority.

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:

pcnt_chan_config_t::edge_gpio_num and pcnt_chan_config_t::level_gpio_num specify the GPIO numbers used by edge type signal and level type signal. Please note, either of them can be assigned to -1 if it is not actually used, and thus it will become a virtual IO. For some simple pulse counting applications where one of the level/edge signals is fixed (i.e., never changes), you can reclaim a GPIO by setting the signal as a virtual IO on channel allocation. Setting the level/edge signal as a virtual IO causes that signal to be internally routed to a fixed High/Low logic level, thus allowing you to save a GPIO for other purposes.
pcnt_chan_config_t::virt_edge_io_level and pcnt_chan_config_t::virt_level_io_level specify the virtual IO level for edge and level input signal, to ensure a deterministic state for such control signal. Please note, they are only valid when either pcnt_chan_config_t::edge_gpio_num or pcnt_chan_config_t::level_gpio_num is assigned to -1.
pcnt_chan_config_t::invert_edge_input and pcnt_chan_config_t::invert_level_input are used to decide whether to invert the input signals before they going into PCNT hardware. The invert is done by GPIO matrix instead of PCNT hardware.
pcnt_chan_config_t::io_loop_back is for debug only, which enables both the GPIO's input and output paths. This can help to simulate the pulse signals by function gpio_set_level() on the same GPIO.

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));

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.

pcnt_channel_set_edge_action() function is to set specific actions for rising and falling edge of the signal attached to the pcnt_chan_config_t::edge_gpio_num. Supported actions are listed in pcnt_channel_edge_action_t.
pcnt_channel_set_level_action() function is to set specific actions for high and low level of the signal attached to the pcnt_chan_config_t::level_gpio_num. Supported actions are listed in pcnt_channel_level_action_t. This function is not mandatory if the pcnt_chan_config_t::level_gpio_num is set to -1 when allocating PCNT channel by pcnt_new_channel().

// 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 data is declared as pcnt_watch_event_data_t:

pcnt_watch_event_data_t::watch_point_value saves the watch point value that triggers the event.
pcnt_watch_event_data_t::zero_cross_mode saves how the PCNT unit crosses the zero point in the latest time. The possible zero cross modes are listed in the pcnt_unit_zero_cross_mode_t. Usually different zero cross mode means different counting direction and counting step size.

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:

Enable pcnt_unit_config_t::accum_count when installing the PCNT unit.

Add the high/low limit as the Watch Points.

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:

Enables the interrupt being serviced even when cache is disabled
Places all functions that used by the ISR into IRAM 2
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:

pcnt_unit_start()
pcnt_unit_stop()
pcnt_unit_clear_count()
pcnt_unit_get_count()

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.

pcnt_unit_start()
pcnt_unit_stop()
pcnt_unit_clear_count()
pcnt_unit_get_count()

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

CONFIG_PCNT_CTRL_FUNC_IN_IRAM controls where to place the PCNT control functions (IRAM or Flash), see IRAM Safe for more information.
CONFIG_PCNT_ISR_IRAM_SAFE controls whether the default ISR handler can work when cache is disabled, see IRAM Safe for more information.
CONFIG_PCNT_ENABLE_DEBUG_LOG is used to enabled the debug log output. Enabling this option increases the firmware binary size.

Application Examples

Decode the quadrature signals from rotary encoder: peripherals/pcnt/rotary_encoder.

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_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

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

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

components/hal/include/hal/pcnt_types.h
This header file can be included with:
#include "hal/pcnt_types.h"

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

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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