Blinky with power management

Overview

This sample is a minimum application to demonstrate basic power management behavior in a basic blinking LED set up using the GPIO API in low power context. Note that lptim instance selected for the low power timer is named &stm32_lp_tick_source When setting a prescaler to decrease the lptimer input clock frequency, the system can sleep for a longer timeout value and the CONFIG_SYS_CLOCK_TICKS_PER_SEC is adjusted. For example, when clocking the low power Timer with LSE clock at 32768Hz and adding a prescaler of <32>, then the kernel sleep period can reach 65536 * 32/32768 = 64 seconds CONFIG_SYS_CLOCK_TICKS_PER_SEC is set to 1024.

Requirements

The board should support enabling PM. For a STM32 based target, it means that it should support a clock source alternative to Cortex Systick that can be used in core sleep states, as LPTIM (st,stm32-lptim).

Building and Running

Build and flash Blinky as follows, changing stm32l562e_dk for your board:

west build -b stm32l562e_dk samples/basic/blinky
west flash

After flashing, the LED starts to blink with a fixed period (SLEEP_TIME_MS). When LPTIM input clock has a prescaler, longer perdiod (up to 64 seconds) of low power can be tested.

PM configurations

By default, CONFIG_PM_DEVICE and CONFIG_PM_DEVICE_RUNTIME are enabled, but user can also deactivate one or the other to see each configuration in play.