Light Sleep

Overview

This example illustrates usage of light sleep mode. Unlike deep sleep mode, light sleep preserves the state of the memory, CPU, and peripherals. Execution of code on both CPUs is stopped when esp_light_sleep_start() function is called. When the chip exits light sleep mode, execution continues at the point where it was stopped, and esp_light_sleep_start() function returns.

The example enables the following wakeup sources:

Timer: wake up the chip in 2 seconds.
EXT0: wake up the chip if a button attached to GPIO0 is pressed (i.e. if GPIO0 goes low).

Requirements

This example can be used with any ESP32 development board. Most boards have a button attached to GPIO0, often labelled BOOT. If the board does not have such button, an external button can be connected, along with a 10k pull-up resistor, and a 100nF capacitor to ground for debouncing.

Building, Flashing and Running

west build -b esp32_devkitc_wroom/esp32/procpu samples/boards/espressif/light_sleep
west flash

Sample Output

ESP32 core output

In the scenario below, the button attached to GPIO0 was pressed and held for about 500 ms, after the second wakeup from light sleep. The program has indicated the wakeup reason after each sleep iteration.

*** Booting Zephyr OS build zephyr-v3.1.0-3667-gb42e2b225ecf  ***

Entering light sleep
Returned from light sleep, reason: timer, t=3344 ms, slept for 2001 ms
Entering light sleep
Returned from light sleep, reason: timer, t=5354 ms, slept for 2000 ms
Entering light sleep
Returned from light sleep, reason: pin, t=5885 ms, slept for 521 ms
Waiting for GPIO0 to go high...
Entering light sleep
Returned from light sleep, reason: timer, t=8765 ms, slept for 2000 ms
Entering light sleep
Returned from light sleep, reason: timer, t=10776 ms, slept for 2001 ms
Entering light sleep

Troubleshooting

If pressing the button attached to GPIO0 does not affect program behavior, check DTR/RTS configuration in the serial monitor. This is not necessary for IDF monitor, but for other tools it might be necessary to set DTR and RTS line state to “disabled” or “de-asserted”.