Sleep Modes

Overview

ESP32 is capable of light sleep and deep sleep power saving modes.

In light sleep mode, digital peripherals, most of the RAM, and CPUs are clock-gated, and supply voltage is reduced. Upon exit from light sleep, peripherals and CPUs resume operation, their internal state is preserved.

In deep sleep mode, CPUs, most of the RAM, and all the digital peripherals which are clocked from APB_CLK are powered off. The only parts of the chip which can still be powered on are: RTC controller, RTC peripherals (including ULP coprocessor), and RTC memories (slow and fast).

Wakeup from deep and light sleep modes can be done using several sources. These sources can be combined, in this case the chip will wake up when any one of the sources is triggered. Wakeup sources can be enabled using esp_sleep_enable_X_wakeup APIs. Next section describes these APIs in detail. Wakeup sources can be configured at any moment before entering light or deep sleep mode.

Additionally, the application can force specific powerdown modes for the RTC peripherals and RTC memories using esp_sleep_pd_config API.

Once wakeup sources are configured, application can enter sleep mode using esp_light_sleep_start or esp_deep_sleep_start APIs. At this point the hardware will be configured according to the requested wakeup sources, and RTC controller will either power down or power off the CPUs and digital peripherals.

WiFi/BT and sleep modes

In deep sleep mode, wireless peripherals are powered down. Before entering sleep mode, applications must disable WiFi and BT using appropriate calls ( esp_bluedroid_disable, esp_bt_controller_disable, esp_wifi_stop).

WiFi can coexist with light sleep mode, allowing the chip to go into light sleep mode when there is no network activity, and waking up the chip from light sleep mode when required. However APIs described in this section can not be used for that purpose. esp_light_sleep_start forces the chip to enter light sleep mode, regardless of whether WiFi is active or not. Automatic entry into light sleep mode, coordinated with WiFi driver, will be supported using a separate set of APIs.

Wakeup sources

Timer

RTC controller has a built in timer which can be used to wake up the chip after a predefined amount of time. Time is specified at microsecond precision, but the actual resolution depends on the clock source selected for RTC SLOW_CLK. See chapter “Reset and Clock” of the ESP32 Technical Reference Manual for details about RTC clock options.

This wakeup mode doesn’t require RTC peripherals or RTC memories to be powered on during sleep.

The following function can be used to enable deep sleep wakeup using a timer.

esp_err_t esp_sleep_enable_timer_wakeup(uint64_t time_in_us)

Enable wakeup by timer.

Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if value is out of range (TBD)
Parameters
  • time_in_us: time before wakeup, in microseconds

Touch pad

RTC IO module contains logic to trigger wakeup when a touch sensor interrupt occurs. You need to configure the touch pad interrupt before the chip starts deep sleep.

Revisions 0 and 1 of the ESP32 only support this wakeup mode when RTC peripherals are not forced to be powered on (i.e. ESP_PD_DOMAIN_RTC_PERIPH should be set to ESP_PD_OPTION_AUTO).

esp_err_t esp_sleep_enable_touchpad_wakeup()

Enable wakeup by touch sensor.

Note
In revisions 0 and 1 of the ESP32, touch wakeup source can not be used when RTC_PERIPH power domain is forced to be powered on (ESP_PD_OPTION_ON) or when ext0 wakeup source is used.
Return
  • ESP_OK on success
  • ESP_ERR_INVALID_STATE if wakeup triggers conflict

External wakeup (ext0)

RTC IO module contains logic to trigger wakeup when one of RTC GPIOs is set to a predefined logic level. RTC IO is part of RTC peripherals power domain, so RTC peripherals will be kept powered on during deep sleep if this wakeup source is requested.

Because RTC IO module is enabled in this mode, internal pullup or pulldown resistors can also be used. They need to be configured by the application using rtc_gpio_pullup_en and rtc_gpio_pulldown_en functions, before calling esp_sleep_start.

In revisions 0 and 1 of the ESP32, this wakeup source is incompatible with ULP and touch wakeup sources.

Warning

After wake up from sleep, IO pad used for wakeup will be configured as RTC IO. Before using this pad as digital GPIO, reconfigure it using rtc_gpio_deinit(gpio_num) function.

esp_err_t esp_sleep_enable_ext0_wakeup(gpio_num_t gpio_num, int level)

Enable wakeup using a pin.

This function uses external wakeup feature of RTC_IO peripheral. It will work only if RTC peripherals are kept on during sleep.

This feature can monitor any pin which is an RTC IO. Once the pin transitions into the state given by level argument, the chip will be woken up.

Note
This function does not modify pin configuration. The pin is configured in esp_sleep_start, immediately before entering sleep mode.
Note
In revisions 0 and 1 of the ESP32, ext0 wakeup source can not be used together with touch or ULP wakeup sources.
Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if the selected GPIO is not an RTC GPIO, or the mode is invalid
  • ESP_ERR_INVALID_STATE if wakeup triggers conflict
Parameters
  • gpio_num: GPIO number used as wakeup source. Only GPIOs which are have RTC functionality can be used: 0,2,4,12-15,25-27,32-39.
  • level: input level which will trigger wakeup (0=low, 1=high)

External wakeup (ext1)

RTC controller contains logic to trigger wakeup using multiple RTC GPIOs. One of the two logic functions can be used to trigger wakeup:

  • wake up if any of the selected pins is high (ESP_EXT1_WAKEUP_ANY_HIGH)
  • wake up if all the selected pins are low (ESP_EXT1_WAKEUP_ALL_LOW)

This wakeup source is implemented by the RTC controller. As such, RTC peripherals and RTC memories can be powered down in this mode. However, if RTC peripherals are powered down, internal pullup and pulldown resistors will be disabled. To use internal pullup or pulldown resistors, request RTC peripherals power domain to be kept on during sleep, and configure pullup/pulldown resistors using rtc_gpio_ functions, before entering sleep:

esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH, ESP_PD_OPTION_ON);
gpio_pullup_dis(gpio_num);
gpio_pulldown_en(gpio_num);

Warning

After wake up from sleep, IO pad(s) used for wakeup will be configured as RTC IO. Before using these pads as digital GPIOs, reconfigure them using rtc_gpio_deinit(gpio_num) function.

The following function can be used to enable this wakeup mode:

esp_err_t esp_sleep_enable_ext1_wakeup(uint64_t mask, esp_sleep_ext1_wakeup_mode_t mode)

Enable wakeup using multiple pins.

This function uses external wakeup feature of RTC controller. It will work even if RTC peripherals are shut down during sleep.

This feature can monitor any number of pins which are in RTC IOs. Once any of the selected pins goes into the state given by mode argument, the chip will be woken up.

Note
This function does not modify pin configuration. The pins are configured in esp_sleep_start, immediately before entering sleep mode.
Note
internal pullups and pulldowns don’t work when RTC peripherals are shut down. In this case, external resistors need to be added. Alternatively, RTC peripherals (and pullups/pulldowns) may be kept enabled using esp_sleep_pd_config function.
Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if any of the selected GPIOs is not an RTC GPIO, or mode is invalid
Parameters
  • mask: bit mask of GPIO numbers which will cause wakeup. Only GPIOs which are have RTC functionality can be used in this bit map: 0,2,4,12-15,25-27,32-39.
  • mode: select logic function used to determine wakeup condition:
    • ESP_EXT1_WAKEUP_ALL_LOW: wake up when all selected GPIOs are low
    • ESP_EXT1_WAKEUP_ANY_HIGH: wake up when any of the selected GPIOs is high

enum esp_sleep_ext1_wakeup_mode_t

Logic function used for EXT1 wakeup mode.

Values:

ESP_EXT1_WAKEUP_ALL_LOW = 0

Wake the chip when all selected GPIOs go low.

ESP_EXT1_WAKEUP_ANY_HIGH = 1

Wake the chip when any of the selected GPIOs go high.

ULP coprocessor wakeup

ULP coprocessor can run while the chip is in sleep mode, and may be used to poll sensors, monitor ADC or touch sensor values, and wake up the chip when a specific event is detected. ULP coprocessor is part of RTC peripherals power domain, and it runs the program stored in RTC slow memeory. RTC slow memory will be powered on during sleep if this wakeup mode is requested. RTC peripherals will be automatically powered on before ULP coprocessor starts running the program; once the program stops running, RTC peripherals are automatically powered down again.

Revisions 0 and 1 of the ESP32 only support this wakeup mode when RTC peripherals are not forced to be powered on (i.e. ESP_PD_DOMAIN_RTC_PERIPH should be set to ESP_PD_OPTION_AUTO).

The following function can be used to enable this wakeup mode:

esp_err_t esp_sleep_enable_ulp_wakeup()

Enable wakeup by ULP coprocessor.

Note
In revisions 0 and 1 of the ESP32, ULP wakeup source can not be used when RTC_PERIPH power domain is forced to be powered on (ESP_PD_OPTION_ON) or when ext0 wakeup source is used.
Return
  • ESP_OK on success
  • ESP_ERR_INVALID_STATE if ULP co-processor is not enabled or if wakeup triggers conflict

Power-down of RTC peripherals and memories

By default, esp_deep_sleep_start and esp_light_sleep_start functions will power down all RTC power domains which are not needed by the enabled wakeup sources. To override this behaviour, esp_sleep_pd_config function is provided.

Note: in revision 0 of the ESP32, RTC fast memory will always be kept enabled in deep sleep, so that the deep sleep stub can run after reset. This can be overriden, if the application doesn’t need clean reset behaviour after deep sleep.

If some variables in the program are placed into RTC slow memory (for example, using RTC_DATA_ATTR attribute), RTC slow memory will be kept powered on by default. This can be overriden using esp_sleep_pd_config function, if desired.

esp_err_t esp_sleep_pd_config(esp_sleep_pd_domain_t domain, esp_sleep_pd_option_t option)

Set power down mode for an RTC power domain in sleep mode.

If not set set using this API, all power domains default to ESP_PD_OPTION_AUTO.

Return
  • ESP_OK on success
  • ESP_ERR_INVALID_ARG if either of the arguments is out of range
Parameters
  • domain: power domain to configure
  • option: power down option (ESP_PD_OPTION_OFF, ESP_PD_OPTION_ON, or ESP_PD_OPTION_AUTO)

enum esp_sleep_pd_domain_t

Power domains which can be powered down in sleep mode.

Values:

ESP_PD_DOMAIN_RTC_PERIPH

RTC IO, sensors and ULP co-processor.

ESP_PD_DOMAIN_RTC_SLOW_MEM

RTC slow memory.

ESP_PD_DOMAIN_RTC_FAST_MEM

RTC fast memory.

ESP_PD_DOMAIN_MAX

Number of domains.

enum esp_sleep_pd_option_t

Power down options.

Values:

ESP_PD_OPTION_OFF

Power down the power domain in sleep mode.

ESP_PD_OPTION_ON

Keep power domain enabled during sleep mode.

ESP_PD_OPTION_AUTO

Keep power domain enabled in sleep mode, if it is needed by one of the wakeup options. Otherwise power it down.

Entering light sleep

The following function can be used to enter light sleep once wakeup sources are configured. It is also possible to go into light sleep with no wakeup sources configured, in this case the chip will be in light sleep mode indefinetly, until external reset is applied.

esp_err_t esp_light_sleep_start()

Enter light sleep with the configured wakeup options.

Return
  • ESP_OK on success (returned after wakeup)
  • ESP_ERR_INVALID_STATE if WiFi or BT is not stopped

Entering deep sleep

The following function can be used to enter deep sleep once wakeup sources are configured. It is also possible to go into deep sleep with no wakeup sources configured, in this case the chip will be in deep sleep mode indefinetly, until external reset is applied.

void esp_deep_sleep_start()

Enter deep sleep with the configured wakeup options.

This function does not return.

Checking sleep wakeup cause

The following function can be used to check which wakeup source has triggered wakeup from sleep mode. For touch pad and ext1 wakeup sources, it is possible to identify pin or touch pad which has caused wakeup.

esp_sleep_wakeup_cause_t esp_sleep_get_wakeup_cause()

Get the source which caused wakeup from sleep.

Return
wakeup cause, or ESP_DEEP_SLEEP_WAKEUP_UNDEFINED if reset happened for reason other than deep sleep wakeup

enum esp_sleep_wakeup_cause_t

Sleep wakeup cause.

Values:

ESP_SLEEP_WAKEUP_UNDEFINED
ESP_SLEEP_WAKEUP_EXT0

In case of deep sleep, reset was not caused by exit from deep sleep.

ESP_SLEEP_WAKEUP_EXT1

Wakeup caused by external signal using RTC_IO.

ESP_SLEEP_WAKEUP_TIMER

Wakeup caused by external signal using RTC_CNTL.

ESP_SLEEP_WAKEUP_TOUCHPAD

Wakeup caused by timer.

ESP_SLEEP_WAKEUP_ULP

Wakeup caused by touchpad.

touch_pad_t esp_sleep_get_touchpad_wakeup_status()

Get the touch pad which caused wakeup.

If wakeup was caused by another source, this function will return TOUCH_PAD_MAX;

Return
touch pad which caused wakeup

uint64_t esp_sleep_get_ext1_wakeup_status()

Get the bit mask of GPIOs which caused wakeup (ext1)

If wakeup was caused by another source, this function will return 0.

Return
bit mask, if GPIOn caused wakeup, BIT(n) will be set

Application Example

Implementation of basic functionality of deep sleep is shown in protocols/sntp example, where ESP module is periodically waken up to retrive time from NTP server.

More extensive example in system/deep_sleep illustrates usage of various deep sleep wakeup triggers and ULP coprocessor programming.