In Light-sleep mode, the digital peripherals, most of the RAM, and CPUs are clock-gated and their supply voltage is reduced. Upon exit from Light-sleep, the digital peripherals, RAM, and CPUs resume operation and their internal states are preserved.
In Deep-sleep mode, the CPUs, most of the RAM, and all digital peripherals that are clocked from APB_CLK are powered off. The only parts of the chip that remain powered on are:
There are several wakeup sources in Deep-sleep and Light-sleep modes. These sources can also be combined so that the chip will wake up when any of the sources are triggered. Wakeup sources can be enabled using ``esp_sleep_enable_X_wakeup`` APIs and can be disabled using :cpp:func:`esp_sleep_disable_wakeup_source` API. Next section describes these APIs in detail. Wakeup sources can be configured at any moment before entering Light-sleep or Deep-sleep mode.
Once wakeup sources are configured, the application can enter sleep mode using :cpp:func:`esp_light_sleep_start` or :cpp:func:`esp_deep_sleep_start` APIs. At this point, the hardware will be configured according to the requested wakeup sources, and the RTC controller will either power down or power off the CPUs and digital peripherals.
In Deep-sleep and Light-sleep modes, the wireless peripherals are powered down. Before entering Deep-sleep or Light-sleep modes, the application must disable Wi-Fi and Bluetooth using the appropriate calls (i.e., :cpp:func:`esp_bluedroid_disable`, :cpp:func:`esp_bt_controller_disable`, :cpp:func:`esp_wifi_stop`). Wi-Fi and Bluetooth connections will not be maintained in Deep-sleep or Light-sleep mode, even if these functions are not called.
In Deep-sleep and Light-sleep modes, the wireless peripherals are powered down. Before entering Deep-sleep or Light-sleep modes, applications must disable Wi-Fi using the appropriate calls (:cpp:func:`esp_wifi_stop`). Wi-Fi connections will not be maintained in Deep-sleep or Light-sleep mode, even if these functions are not called.
If Wi-Fi connections need to be maintained, enable Wi-Fi Modem-sleep mode and automatic Light-sleep feature (see :doc:`Power Management APIs <power_management>`). This will allow the system to wake up from sleep automatically when required by the Wi-Fi driver, thereby maintaining a connection to the AP.
The 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.
The RTC IO module contains the logic to trigger wakeup when a touch sensor interrupt occurs. To wakeup from a touch sensor interrupt, users need to configure the touch pad interrupt before the chip enters Deep-sleep or Light-sleep modes.
Revisions 0 and 1 of 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 RTC IO module contains the logic to trigger wakeup when one of RTC GPIOs is set to a predefined logic level. RTC IO is part of the RTC peripherals power domain, so RTC peripherals will be kept powered on during Deep-sleep if this wakeup source is requested.
The RTC IO module is enabled in this mode, so internal pullup or pulldown resistors can also be used. They need to be configured by the application using :cpp:func:`rtc_gpio_pullup_en` and :cpp:func:`rtc_gpio_pulldown_en` functions before calling :cpp:func:`esp_deep_sleep_start`.
..warning:: After waking up from sleep, the IO pad used for wakeup will be configured as RTC IO. Therefore, before using this pad as digital GPIO, users need to reconfigure it using :cpp:func:`rtc_gpio_deinit` function.
The RTC controller contains the logic to trigger wakeup using multiple RTC GPIOs. One of the following two logic functions can be used to trigger wakeup:
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 the RTC peripherals power domain to be kept on during sleep, and configure pullup/pulldown resistors using ``rtc_gpio_`` functions before entering sleep::
..warning:: After waking 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 :cpp:func:`rtc_gpio_deinit` function.
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 the RTC peripherals power domain, and it runs the program stored in RTC slow memory. 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 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).
In addition to EXT0 and EXT1 wakeup sources described above, one more method of wakeup from external inputs is available in Light-sleep mode. With this wakeup source, each pin can be individually configured to trigger wakeup on high or low level using :cpp:func:`gpio_wakeup_enable` function. Unlike EXT0 and EXT1 wakeup sources, which can only be used with RTC IOs, this wakeup source can be used with any IO (RTC or digital).
One more method of wakeup from external inputs is available in Light-sleep mode. With this wakeup source, each pin can be individually configured to trigger wakeup on high or low level using :cpp:func:`gpio_wakeup_enable` function. This wakeup source can be used with any IO (RTC or digital).
Before entering Light-sleep mode, check if any GPIO pin to be driven is part of the {IDF_TARGET_SPI_POWER_DOMAIN} power domain. If so, this power domain must be configured to remain ON during sleep.
For example, on ESP32-WROOM-32 board, GPIO16 and GPIO17 are linked to {IDF_TARGET_SPI_POWER_DOMAIN} power domain. If they are configured to remain high during Light-sleep, the power domain should be configured to remain powered ON. This can be done with :cpp:func:`esp_sleep_pd_config()`::
When {IDF_TARGET_NAME} receives UART input from external devices, it is often necessary to wake up the chip when input data is available. The UART peripheral contains a feature which allows waking up the chip from Light-sleep when a certain number of positive edges on RX pin are seen. This number of positive edges can be set using :cpp:func:`uart_set_wakeup_threshold` function. Note that the character which triggers wakeup (and any characters before it) will not be received by the UART after wakeup. This means that the external device typically needs to send an extra character to the {IDF_TARGET_NAME} to trigger wakeup before sending the data.
By default, :cpp:func:`esp_deep_sleep_start` and :cpp:func:`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, :cpp:func:`esp_sleep_pd_config` function is provided.
Note: in revision 0 of 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 overridden, 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 overridden using :cpp:func:`esp_sleep_pd_config` function, if desired.
In {IDF_TARGET_NAME}, there is only RTC fast memory, so if some variables in the program are marked by ``RTC_DATA_ATTR``, ``RTC_SLOW_ATTR`` or ``RTC_FAST_ATTR`` attributes, all of them go to RTC fast memory. It will be kept powered on by default. This can be overridden using :cpp:func:`esp_sleep_pd_config` function, if desired.
By default, to avoid potential issues, :cpp:func:`esp_light_sleep_start` function will **not** power down flash. To be more specific, it takes time to power down the flash and during this period the system may be woken up, which then actually powers up the flash before this flash could be powered down completely. As a result, there is a chance that the flash may not work properly.
So, in theory, it's ok if you only wake up the system after the flash is completely powered down. However, in reality, the flash power-down period can be hard to predict (for example, this period can be much longer when you add filter capacitors to the flash's power supply circuit) and uncontrollable (for example, the asynchronous wake-up signals make the actual sleep time uncontrollable).
..warning::
If a filter capacitor is added to your flash power supply circuit, please do everything possible to avoid powering down flash.
Therefore, it's recommended not to power down flash when using ESP-IDF. For power-sensitive applications, it's recommended to use Kconfig option :ref:`CONFIG_ESP_SLEEP_FLASH_LEAKAGE_WORKAROUND` to reduce the power consumption of the flash during light sleep, instead of powering down the flash.
It is worth mentioning that PSRAM has a similar Kconfig option :ref:`CONFIG_ESP_SLEEP_PSRAM_LEAKAGE_WORKAROUND`.
However, for those who have fully understood the risk and are still willing to power down the flash to further reduce the power consumption, please check the following mechanisms:
..list::
- Setting Kconfig option :ref:`CONFIG_ESP_SLEEP_POWER_DOWN_FLASH` only powers down the flash when the RTC timer is the only wake-up source **and** the sleep time is longer than the flash power-down period.
- Calling ``esp_sleep_pd_config(ESP_PD_DOMAIN_VDDSDIO, ESP_PD_OPTION_OFF)`` powers down flash when the RTC timer is not enabled as a wakeup source **or** the sleep time is longer than the flash power-down period.
:cpp:func:`esp_light_sleep_start` function can be used to enter Light-sleep once wakeup sources are configured. It is also possible to enter Light-sleep with no wakeup sources configured. In this case, the chip will be in Light-sleep mode indefinitely until external reset is applied.
:cpp:func:`esp_deep_sleep_start` function can be used to enter Deep-sleep once wakeup sources are configured. It is also possible to enter Deep-sleep with no wakeup sources configured. In this case, the chip will be in Deep-sleep mode indefinitely until external reset is applied.
Some {IDF_TARGET_NAME} IOs have internal pullups or pulldowns, which are enabled by default. If an external circuit drives this pin in Deep-sleep mode, current consumption may increase due to current flowing through these pullups and pulldowns.
To isolate a pin to prevent extra current draw, call :cpp:func:`rtc_gpio_isolate` function.
For example, on ESP32-WROVER module, GPIO12 is pulled up externally, and it also has an internal pulldown in the ESP32 chip. This means that in Deep-sleep, some current will flow through these external and internal resistors, increasing Deep-sleep current above the minimal possible value.
When entering Light-sleep mode using :cpp:func:`esp_light_sleep_start`, UART FIFOs will not be flushed. Instead, UART output will be suspended, and remaining characters in the FIFO will be sent out after wakeup from Light-sleep.
Previously configured wakeup sources can be disabled later using :cpp:func:`esp_sleep_disable_wakeup_source` API. This function deactivates trigger for the given wakeup source. Additionally, it can disable all triggers if the argument is ``ESP_SLEEP_WAKEUP_ALL``.
-:example:`protocols/sntp`: the implementation of basic functionality of Deep-sleep, where ESP module is periodically waken up to retrieve time from NTP server.
