The [deep sleep mode](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/sleep_modes.html#sleep-modes) is a power saving mode that causes the CPU, majority of RAM, and digital peripherals that are clocked from APB_CLK to be powered off. Deep sleep mode can be exited using one of multiple [wake up sources](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/sleep_modes.html#wakeup-sources). This example demonstrates how to use the [`esp_sleep.h`](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/sleep_modes.html#api-reference) API to enter deep sleep mode, then wake up form different sources.
The following wake up sources are demonstrated in this example (refer to the [Wakeup Sources documentation](https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/system/sleep_modes.html#wakeup-sources) for more details regarding wake up sources):
- **Timer:** An RTC timer that can be programmed to trigger a wake up after a preset time. This example will trigger a wake up every 20 seconds.
- **EXT0:** External wake up 0 can trigger wakeup when one predefined RTC GPIO is at a predefined logic level. This example uses GPIO25 in ESP32 or GPIO3 in ESP32-S2/S3 to trigger a wake up when the pin is HIGH. (This wake up source is only available on ESP32, ESP32-S2, and ESP32-S3.)
- **EXT1:** External wake up 1 which is tied to multiple RTC GPIOs. This example uses GPIO2 and GPIO4 to trigger a wake up with any one of the two pins are HIGH. (This wake up source is only available on ESP32, ESP32-S2, and ESP32-S3.)
- **GPIO:** Pads powered by VDD3P3_RTC can be used to trigger a wake up from deep sleep. You may choose the pin and trigger level in menuconfig. (This wake up source is unavailable on ESP32, ESP32-S2, and ESP32-S3.)
- **Touch:** Touch pad sensor interrupt. This example uses touch pads connected to GPIO32, GPIO33 in ESP32 or GPIO9 in ESP32-S2/S3 to trigger a wake up when any of the pads are pressed.
- **ULP:** Ultra Low Power Coprocessor which can continue to run during deep sleep. This example utilizes the ULP and constantly sample the chip's temperature and trigger a wake up if the chips temperature exceeds ~5 degrees Celsius.
Warning: On ESP32, touch wake up source cannot be used together with EXT0 or ULP wake up source. If they co-exist, IDF will give a runtime error and the program will crash. By default in this example, touch wake up is enabled, and the other two are disabled. You can switch to enable the other wake up sources via menuconfig.
In this example, the `CONFIG_BOOTLOADER_SKIP_VALIDATE_IN_DEEP_SLEEP` Kconfig option is used, which allows you to reduce the boot time of the bootloader during waking up from deep sleep. The bootloader stores in rtc memory the address of a running partition and uses it when it wakes up. This example allows you to skip all image checks and speed up the boot.
This example should be able to run on any commonly available ESP32 series development board without any extra hardware if only **Timer** and **ULP** wake up sources are used. However, the following extra connections will be required for the remaining wake up sources.
- **EXT0:** Connect GPIO25 in ESP32 or GPIO3 in ESP32-S2/S3 to HIGH to trigger a wake up.
- **EXT1:** GPIO2 and GPIO4 should be connected to LOW to avoid floating pins. When triggering a wake up, connect one or both of the pins to HIGH. Note that floating pins may trigger a wake up.
- **GPIO:** If `EXAMPLE_GPIO_WAKEUP_HIGH_LEVEL` is selected in menuconfig, then connect `EXAMPLE_GPIO_WAKEUP_PIN` to HIGH to trigger a wake up; Otherwise, connect `EXAMPLE_GPIO_WAKEUP_PIN` to LOW to trigger a wake up.
- **Touch:** GPIO32, GPIO33 in ESP32 or GPIO9 in ESP32-S2/S3 should be connected to touch sensors (see [Touch Sensor Application Note](https://github.com/espressif/esp-iot-solution/blob/release/v1.0/documents/touch_pad_solution/touch_sensor_design_en.md)).
Wake up sources that are unused or unconnected should be disabled in configuration to prevent inadvertent triggering of wake up as a result of floating pins.
### Build and Flash
Build the project and flash it to the board, then run monitor tool to view serial output:
```
idf.py -p PORT flash monitor
```
(Replace PORT with the name of the serial port to use.)
(To exit the serial monitor, type ``Ctrl-]``.)
See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
## Example Output
On initial startup, this example will detect that this is the first boot and output the following low:
Touch pad #8 average: 2148, wakeup threshold set to 2048.
Touch pad #9 average: 2148, wakeup threshold set to 2048.
Enabling touch pad wakeup
Enabling ULP wakeup
Entering deep sleep
```
The ESP32 will then enter deep sleep. When a wake up occurs, the ESP32 must undergo the entire boot process again. However the example will detect that this boot is due to a wake up and indicate the wake up source in the output log such as the following:
```
...
I (304) cpu_start: Starting scheduler on PRO CPU.
I (0) cpu_start: Starting scheduler on APP CPU.
Wake up from timer. Time spent in deep sleep: 20313ms
