Standby mode behavior in Embedded C

Introduction

Standby mode helps save power by putting the device into a very low energy state when it is not active.

When a device needs to save battery during long idle times.

In wearable devices that must last many hours without charging.

For sensors that only need to wake up occasionally to take measurements.

In remote controls that wait for user input but should use minimal power.

When a system must quickly resume full operation after sleeping.

Syntax

Embedded C

void enter_standby_mode(void) {
    // Prepare device for standby
    // Configure wake-up sources
    // Enter standby mode instruction
}

The exact code to enter standby mode depends on the microcontroller used.

Wake-up sources must be configured before entering standby to resume operation.

Examples

This example shows how to enter standby mode on an STM32 by setting specific registers and then waiting for an interrupt.

Embedded C

/* Example for STM32 microcontroller */
PWR->CR |= PWR_CR_PDDS; // Set Power Down Deep Sleep
SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk; // Set SLEEPDEEP bit
__WFI(); // Wait For Interrupt to enter standby

A simplified example where functions handle wake-up setup and entering standby.

Embedded C

/* Example for generic MCU */
set_wakeup_source();
enter_standby();

Sample Program

This program simulates entering standby mode by setting flags and printing messages. In a real embedded system, the __WFI() instruction would put the CPU to sleep until an interrupt wakes it.

Embedded C

#include <stdint.h>
#include <stdio.h>

// Simulated registers for demonstration
volatile uint32_t PWR_CR = 0;
volatile uint32_t SCB_SCR = 0;

#define PWR_CR_PDDS (1 << 1)
#define SCB_SCR_SLEEPDEEP_Msk (1 << 2)

void enter_standby_mode(void) {
    printf("Preparing to enter standby mode...\n");
    PWR_CR |= PWR_CR_PDDS; // Set power down deep sleep
    SCB_SCR |= SCB_SCR_SLEEPDEEP_Msk; // Set sleep deep bit
    printf("Standby mode entered. Waiting for interrupt...\n");
    // __WFI(); // In real MCU, this would wait for interrupt
}

int main(void) {
    printf("System running normally.\n");
    enter_standby_mode();
    printf("System woke up from standby.\n");
    return 0;
}

Important Notes

Standby mode usually stops most clocks and reduces power to peripherals.

Wake-up sources can be buttons, timers, or external signals.

Always configure wake-up sources before entering standby to avoid being stuck.

Summary

Standby mode saves power by putting the device into a deep sleep state.

You must set specific registers and configure wake-up sources before entering standby.

The device wakes up when a configured event or interrupt occurs.