Power Management

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Overview

Power management algorithm included in ESP-IDF can adjust the advanced peripheral bus (APB) frequency, CPU frequency, and put the chip into light sleep mode to run an application at smallest possible power consumption, given the requirements of application components.

Application components can express their requirements by creating and acquiring power management locks.

For example:

  • Driver for a peripheral clocked from APB can request the APB frequency to be set to 80 MHz while the peripheral is used.
  • RTOS can request the CPU to run at the highest configured frequency while there are tasks ready to run.
  • A peripheral driver may need interrupts to be enabled, which means it will have to request disabling light sleep.

Since requesting higher APB or CPU frequencies or disabling light sleep causes higher current consumption, please keep the usage of power management locks by components to a minimum.

Configuration

Power management can be enabled at compile time, using the option CONFIG_PM_ENABLE.

Enabling power management features comes at the cost of increased interrupt latency. Extra latency depends on a number of factors, such as the CPU frequency, single/dual core mode, whether or not frequency switch needs to be done. Minimum extra latency is 0.2 us (when the CPU frequency is 240 MHz and frequency scaling is not enabled). Maximum extra latency is 40 us (when frequency scaling is enabled, and a switch from 40 MHz to 80 MHz is performed on interrupt entry).

Dynamic frequency scaling (DFS) and automatic light sleep can be enabled in an application by calling the function esp_pm_configure(). Its argument is a structure defining the frequency scaling settings, esp_pm_config_esp32_t. In this structure, three fields need to be initialized:

  • max_freq_mhz: Maximum CPU frequency in MHz, i.e., the frequency used when the ESP_PM_CPU_FREQ_MAX lock is acquired. This field will usually be set to CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ.
  • min_freq_mhz: Minimum CPU frequency in MHz, i.e., the frequency used when only the ESP_PM_APB_FREQ_MAX lock is acquired. This field can be set to the XTAL frequency value, or the XTAL frequency divided by an integer. Note that 10 MHz is the lowest frequency at which the default REF_TICK clock of 1 MHz can be generated.
  • light_sleep_enable: Whether the system should automatically enter light sleep when no locks are acquired (true/false).

Alternatively, if you enable the option CONFIG_PM_DFS_INIT_AUTO in menuconfig, the maximum CPU frequency will be determined by the CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ setting, and the minimum CPU frequency will be locked to the XTAL frequency.

Note

Automatic light sleep is based on FreeRTOS Tickless Idle functionality. If automatic light sleep is requested while the option CONFIG_FREERTOS_USE_TICKLESS_IDLE is not enabled in menuconfig, esp_pm_configure() will return the error ESP_ERR_NOT_SUPPORTED.

Note

In light sleep, peripherals are clock gated, and interrupts (from GPIOs and internal peripherals) will not be generated. A wakeup source described in the Sleep Modes documentation can be used to trigger wakeup from the light sleep state. For example, the EXT0 and EXT1 wakeup sources can be used to wake up the chip via a GPIO.

Power Management Locks

Applications have the ability to acquire/release locks in order to control the power management algorithm. When an application acquires a lock, the power management algorithm operation is restricted in a way described below. When the lock is released, such restrictions are removed.

Power management locks have acquire/release counters. If the lock has been acquired a number of times, it needs to be released the same number of times to remove associated restrictions.

ESP32 supports three types of locks described in the table below.

Lock Description
ESP_PM_CPU_FREQ_MAX Requests CPU frequency to be at the maximum value set with esp_pm_configure(). For ESP32, this value can be set to 80 MHz, 160 MHz, or 240 MHz.
ESP_PM_APB_FREQ_MAX Requests the APB frequency to be at the maximum supported value. For ESP32, this is 80 MHz.
ESP_PM_NO_LIGHT_SLEEP Disables automatic switching to light sleep.

ESP32 Power Management Algorithm

The table below shows how CPU and APB frequencies will be switched if dynamic frequency scaling is enabled. You can specify the maximum CPU frequency with either esp_pm_configure() or CONFIG_ESP32_DEFAULT_CPU_FREQ_MHZ.

Max CPU Frequency Set Lock Acquisition CPU and APB Frequncies
240
Any of ESP_PM_CPU_FREQ_MAX
or ESP_PM_APB_FREQ_MAX acquired
CPU: 240 MHz
APB: 80 MHz
None Min values for both frequencies set with esp_pm_configure()
160 ESP_PM_CPU_FREQ_MAX acquired
CPU: 160 MHz
APB: 80 MHz
ESP_PM_CPU_FREQ_MAX acquired, ESP_PM_APB_FREQ_MAX not acquired
CPU: 80 MHz
APB: 80 MHz
None Min values for both frequencies set with esp_pm_configure()
80
Any of ESP_PM_CPU_FREQ_MAX
or ESP_PM_APB_FREQ_MAX acquired
CPU: 80 MHz
APB: 80 MHz
None Min values for both frequencies set with esp_pm_configure()

If none of the locks are acquired, and light sleep is enabled in a call to esp_pm_configure(), the system will go into light sleep mode. The duration of light sleep will be determined by:

Light sleep duration will be chosen to wake up the chip before the nearest event (task being unblocked, or timer elapses).

Dynamic Frequency Scaling and Peripheral Drivers

When DFS is enabled, the APB frequency can be changed multiple times within a single RTOS tick. The APB frequency change does not affect the work of some peripherals, while other peripherals may have issues. For example, Timer Group peripheral timers will keep counting, however, the speed at which they count will change proportionally to the APB frequency.

The following peripherals work normally even when the APB frequency is changing:

  • UART: if REF_TICK is used as a clock source. See use_ref_tick member of uart_config_t.
  • LEDC: if REF_TICK is used as a clock source. See ledc_timer_config() function.
  • RMT: if REF_TICK is used as a clock source. Although the driver does not support REF_TICK, this feature can be enabled by clearing the RMT_REF_ALWAYS_ON_CHx bit for the respective channel.

Currently, the following peripheral drivers are aware of DFS and will use the ESP_PM_APB_FREQ_MAX lock for the duration of the transaction:

  • SPI master
  • I2C
  • I2S (If the APLL clock is used, then it will use the ESP_PM_NO_LIGHT_SLEEP lock)
  • SDMMC

The following drivers will hold the ESP_PM_APB_FREQ_MAX lock while the driver is enabled:

The following peripheral drivers are not aware of DFS yet. Applications need to acquire/release locks themselves, when necessary:

  • MCPWM
  • PCNT
  • Sigma-delta
  • Timer group

API Reference

Functions

esp_err_t esp_pm_configure(const void *config)

Set implementation-specific power management configuration.

Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if the configuration values are not correct
  • ESP_ERR_NOT_SUPPORTED if certain combination of values is not supported, or if CONFIG_PM_ENABLE is not enabled in sdkconfig
Parameters
  • config: pointer to implementation-specific configuration structure (e.g. esp_pm_config_esp32)

esp_err_t esp_pm_lock_create(esp_pm_lock_type_t lock_type, int arg, const char *name, esp_pm_lock_handle_t *out_handle)

Initialize a lock handle for certain power management parameter.

When lock is created, initially it is not taken. Call esp_pm_lock_acquire to take the lock.

This function must not be called from an ISR.

Return
  • ESP_OK on success
  • ESP_ERR_NO_MEM if the lock structure can not be allocated
  • ESP_ERR_INVALID_ARG if out_handle is NULL or type argument is not valid
  • ESP_ERR_NOT_SUPPORTED if CONFIG_PM_ENABLE is not enabled in sdkconfig
Parameters
  • lock_type: Power management constraint which the lock should control
  • arg: argument, value depends on lock_type, see esp_pm_lock_type_t
  • name: arbitrary string identifying the lock (e.g. “wifi” or “spi”). Used by the esp_pm_dump_locks function to list existing locks. May be set to NULL. If not set to NULL, must point to a string which is valid for the lifetime of the lock.
  • out_handle: handle returned from this function. Use this handle when calling esp_pm_lock_delete, esp_pm_lock_acquire, esp_pm_lock_release. Must not be NULL.

esp_err_t esp_pm_lock_acquire(esp_pm_lock_handle_t handle)

Take a power management lock.

Once the lock is taken, power management algorithm will not switch to the mode specified in a call to esp_pm_lock_create, or any of the lower power modes (higher numeric values of ‘mode’).

The lock is recursive, in the sense that if esp_pm_lock_acquire is called a number of times, esp_pm_lock_release has to be called the same number of times in order to release the lock.

This function may be called from an ISR.

This function is not thread-safe w.r.t. calls to other esp_pm_lock_* functions for the same handle.

Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if the handle is invalid
  • ESP_ERR_NOT_SUPPORTED if CONFIG_PM_ENABLE is not enabled in sdkconfig
Parameters
  • handle: handle obtained from esp_pm_lock_create function

esp_err_t esp_pm_lock_release(esp_pm_lock_handle_t handle)

Release the lock taken using esp_pm_lock_acquire.

Call to this functions removes power management restrictions placed when taking the lock.

Locks are recursive, so if esp_pm_lock_acquire is called a number of times, esp_pm_lock_release has to be called the same number of times in order to actually release the lock.

This function may be called from an ISR.

This function is not thread-safe w.r.t. calls to other esp_pm_lock_* functions for the same handle.

Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if the handle is invalid
  • ESP_ERR_INVALID_STATE if lock is not acquired
  • ESP_ERR_NOT_SUPPORTED if CONFIG_PM_ENABLE is not enabled in sdkconfig
Parameters
  • handle: handle obtained from esp_pm_lock_create function

esp_err_t esp_pm_lock_delete(esp_pm_lock_handle_t handle)

Delete a lock created using esp_pm_lock.

The lock must be released before calling this function.

This function must not be called from an ISR.

Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if the handle argument is NULL
  • ESP_ERR_INVALID_STATE if the lock is still acquired
  • ESP_ERR_NOT_SUPPORTED if CONFIG_PM_ENABLE is not enabled in sdkconfig
Parameters
  • handle: handle obtained from esp_pm_lock_create function

esp_err_t esp_pm_dump_locks(FILE *stream)

Dump the list of all locks to stderr

This function dumps debugging information about locks created using esp_pm_lock_create to an output stream.

This function must not be called from an ISR. If esp_pm_lock_acquire/release are called while this function is running, inconsistent results may be reported.

Return
  • ESP_OK on success
  • ESP_ERR_NOT_SUPPORTED if CONFIG_PM_ENABLE is not enabled in sdkconfig
Parameters
  • stream: stream to print information to; use stdout or stderr to print to the console; use fmemopen/open_memstream to print to a string buffer.

Type Definitions

typedef struct esp_pm_lock *esp_pm_lock_handle_t

Opaque handle to the power management lock.

Enumerations

enum esp_pm_lock_type_t

Power management constraints.

Values:

ESP_PM_CPU_FREQ_MAX

Require CPU frequency to be at the maximum value set via esp_pm_configure. Argument is unused and should be set to 0.

ESP_PM_APB_FREQ_MAX

Require APB frequency to be at the maximum value supported by the chip. Argument is unused and should be set to 0.

ESP_PM_NO_LIGHT_SLEEP

Prevent the system from going into light sleep. Argument is unused and should be set to 0.

Structures

struct esp_pm_config_esp32_t

Power management config for ESP32.

Pass a pointer to this structure as an argument to esp_pm_configure function.

Public Members

int max_freq_mhz

Maximum CPU frequency, in MHz

int min_freq_mhz

Minimum CPU frequency to use when no locks are taken, in MHz

bool light_sleep_enable

Enter light sleep when no locks are taken