How to reduce power consumption in deep sleep modes using C on ARM Cortex-M?

Understand the Deep Sleep Modes

Before diving into the specifics of optimizing power consumption, it's crucial to understand the available sleep modes of the ARM Cortex-M architecture. The ARM Cortex-M family usually includes several levels of sleep modes, such as Sleep, Deep Sleep, and Standby. Deep Sleep and Standby modes offer substantial power savings but may result in slower wake-up times or require more complex wake-up mechanisms.

Use the Power Control (PWR) Peripheral

The Power Control (PWR) peripheral manages the low-power mode transitions. Ensure that your microcontroller is configured properly to manage its power distributions using the PWR controls.

#include "stm32f4xx_hal.h"

void EnterDeepSleepMode(void) {
    // Enable Power Control clock
    __HAL_RCC_PWR_CLK_ENABLE();

    // Set the regulator to low-power mode
    HAL_PWREx_EnableLowPowerRunMode();

    // Set the SleepDeep bit to enable deep sleep mode
    SCB->SCR |= SCB_SCR_SLEEPDEEP_Msk;

    // Request deep sleep mode
    __WFI();
}

Optimize Peripheral Usage

To minimize power consumption, disable the peripherals that aren't necessary during the deep sleep period. Consider disabling clocks for unused peripherals or using clock gating to minimize power usage.

void DisableUnusedPeripherals(void) {
    // For example, disable GPIO clocks
    __HAL_RCC_GPIOA_CLK_DISABLE();
    __HAL_RCC_GPIOB_CLK_DISABLE();
    // Disable other peripheral clocks as needed
}

Reduce Clock Speeds Before Entering Sleep

Lowering the system clock frequency before entering deep sleep can substantially reduce power consumption. Configure the system to use the lowest frequency that still meets your performance requirements before sleep.

void ConfigureLowClockSpeed(void) {
    // Change system clock source to a slower clock
    RCC_ClkInitTypeDef clkInitStruct = {};
    RCC_OscInitTypeDef oscInitStruct = {};

    oscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
    oscInitStruct.HSIState = RCC_HSI_ON;
    oscInitStruct.PLL.PLLState = RCC_PLL_NONE;
    HAL_RCC_OscConfig(&oscInitStruct);

    clkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2);
    clkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
    clkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV8;
    clkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
    clkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
    HAL_RCC_ClockConfig(&clkInitStruct, FLASH_LATENCY_0);
}

Utilize Wake-Up Sources Wisely

Configuring the appropriate wake-up sources is essential for reliable operation. Use external interrupts, RTC alarms, or other methods to wake the microcontroller from deep sleep. The correct configuration ensures that the microcontroller wakes only when necessary.

void ConfigureWakeUpSource(void) {
    // Configure an external interrupt as a wake-up source
    HAL_NVIC_EnableIRQ(EXTI0_IRQn);

    // Enable RTC Wake-up
    __HAL_RTC_WAKEUPTIMER_ENABLE_IT(&hrtc, RTC_IT_WUT);
}

Minimize Flash and RAM Usage

Reduce the memory footprint of your application to limit power usage. Use the smallest realistic data types, optimize your algorithms, and remove unnecessary debug information or data logging.

Utilize Software Techniques

Implement software strategies such as event-driven programming to avoid polling, reducing active CPU time. Use DMA when transferring data to free the CPU for other tasks or sleep states.

By carefully managing peripherals, configuring appropriate wake-up sources, and optimizing clock and memory usage, you can significantly reduce power consumption in deep sleep modes on ARM Cortex-M microcontrollers.