LP Timer Wakeup

Browse source code on GitHub

Overview

This sample demonstrates the LP core using the LP timer to periodically wake the HP core from deep sleep. The LP core operates in a one-shot model: it wakes up, signals the HP core, re-arms the LP timer using the sleep duration configured by the HP core via shared memory, and halts until the next timer alarm.

The HP core boots, prints its wake count, and enters deep sleep via sys_poweroff(). A RTC_DATA_ATTR variable tracks the number of wakeups across deep sleep cycles.

The sleep duration is configured via CONFIG_ESP32_ULP_LP_CORE_LP_TIMER_SLEEP_DURATION_US (default: 2000000 us = 2 seconds).

How it works

  1. HP core loads LP core binary, configures LP timer wakeup source with the desired sleep duration, and enters deep sleep.

  2. LP core wakes from LP timer alarm, calls ulp_lp_core_wakeup_main_processor() to wake the HP core.

  3. LP core reads the pre-computed sleep duration (in ticks) from shared memory and re-arms the LP timer for the next cycle.

  4. LP core calls ulp_lp_core_halt() to enter low-power sleep.

  5. On the next LP timer alarm, the LP core resets and repeats from step 2.

Building and Flashing

Build the sample code as follows:

west build -b esp32c6_devkitc/esp32c6/hpcore --sysbuild samples/boards/espressif/ulp/lp_core/timer_wakeup

Flash it to the device with the command:

west build -b esp32c6_devkitc/esp32c6/hpcore samples/boards/espressif/ulp/lp_core/timer_wakeup
west flash

Sample Output

First boot, LP core will wake us every 2000 ms
HP core entering deep sleep...

After wakeup:

Woke up from LP core (LP timer)! Wake count: 1
HP core entering deep sleep...