很多MCU都有低功耗模式，以满足对功耗要求苛刻的应用场景。STM32系列MCU的低功耗模式根据其内核与类型的不同也各不相同，网上有很多文章介绍。本文总结下STM32L051的STOP模式，通过RTC唤醒。
STM32L051在低功耗方面性能优异，ST官方数据手册中说明，在stop without rtc模式下电流消耗能达到0.4uA，在stop with rtc模式下电流消耗能达到0.8uA。
在进入STOP模式前对外设进行设置，GPIO要设置成模拟输入状态。
static void system_config_before_stop(void){HAL_StatusTypeDef ret = HAL_OK;GPIO_InitTypeDef GPIO_InitStructure;/* Enable Ultra low power mode */HAL_PWREx_EnableUltraLowPower();/* Enable the fast wake up from Ultra low power mode */HAL_PWREx_EnableFastWakeUp();/* Select HSI as system clock source after Wake Up from Stop mode */__HAL_RCC_WAKEUPSTOP_CLK_CONFIG(RCC_STOP_WAKEUPCLOCK_HSI);/* Enable GPIOs clock */__HAL_RCC_GPIOA_CLK_ENABLE();__HAL_RCC_GPIOB_CLK_ENABLE();__HAL_RCC_GPIOC_CLK_ENABLE();/* Configure all GPIO port pins in Analog Input mode (floating input trigger OFF) */GPIO_InitStructure.Pin = GPIO_PIN_All;GPIO_InitStructure.Mode = GPIO_MODE_ANALOG;GPIO_InitStructure.Pull = GPIO_NOPULL;HAL_GPIO_Init(GPIOA, &GPIO_InitStructure);HAL_GPIO_Init(GPIOB, &GPIO_InitStructure);HAL_GPIO_Init(GPIOC, &GPIO_InitStructure);/* Disable GPIOs clock */__HAL_RCC_GPIOA_CLK_DISABLE();__HAL_RCC_GPIOB_CLK_DISABLE();__HAL_RCC_GPIOC_CLK_DISABLE();/* Configure RTC */RTCHandle.Instance = RTC;RTCHandle.Init.HourFormat = RTC_HOURFORMAT_24;RTCHandle.Init.AsynchPrediv = RTC_ASYNCH_PREDIV;RTCHandle.Init.SynchPrediv = RTC_SYNCH_PREDIV;RTCHandle.Init.OutPut = RTC_OUTPUT_DISABLE;RTCHandle.Init.OutPutPolarity = RTC_OUTPUT_POLARITY_HIGH;RTCHandle.Init.OutPutType = RTC_OUTPUT_TYPE_OPENDRAIN;ret = HAL_RTC_Init(&RTCHandle);if (ret != HAL_OK) while (1);}
设置RTC的唤醒时间，函数参数单位为秒。
static void stop_rtc_config(uint32_t sleep){/* Disable Wakeup Counter */HAL_RTCEx_DeactivateWakeUpTimer(&RTCHandle);/*## Setting the Wake up time */HAL_RTCEx_SetWakeUpTimer_IT(&RTCHandle, sleep, RTC_WAKEUPCLOCK_CK_SPRE_16BITS);}
调用库函数进入STOP模式。
HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
退出STOP模式后要恢复时钟。特别注意在进入STOP模式后系统时钟变成了MSI。
static void clock_config_after_stop(void){HAL_StatusTypeDef ret = HAL_OK;RCC_OscInitTypeDef RCC_OscInitStructure = {0};RCC_ClkInitTypeDef RCC_ClkInitStructure = {0};/* Enable Power Control clock */__HAL_RCC_PWR_CLK_ENABLE();/* The voltage scaling allows optimizing the power consumption when the device isclocked below the maximum system frequency, to update the voltage scaling valueregarding system frequency refer to product datasheet. */__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);/* Get the Oscillators configuration according to the internal RCC registers */HAL_RCC_GetOscConfig(&RCC_OscInitStructure);/* After wake-up from STOP reconfigure the system clock: Enable HSI and PLL */RCC_OscInitStructure.OscillatorType = RCC_OSCILLATORTYPE_HSI;RCC_OscInitStructure.HSEState = RCC_HSE_OFF;RCC_OscInitStructure.HSIState = RCC_HSI_ON;RCC_OscInitStructure.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;RCC_OscInitStructure.PLL.PLLState = RCC_PLL_ON;RCC_OscInitStructure.PLL.PLLSource = RCC_PLLSOURCE_HSI;RCC_OscInitStructure.PLL.PLLMUL = RCC_PLLMUL_4;RCC_OscInitStructure.PLL.PLLDIV = RCC_PLLDIV_2;ret = HAL_RCC_OscConfig(&RCC_OscInitStructure);if (ret != HAL_OK) while (1);/* Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2clocks dividers */RCC_ClkInitStructure.ClockType = RCC_CLOCKTYPE_SYSCLK;RCC_ClkInitStructure.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;ret = HAL_RCC_ClockConfig(&RCC_ClkInitStructure, FLASH_LATENCY_1);if (ret != HAL_OK) while (1);}
恢复各外设状态，比如GPIO、串口等初始化。
static void gpioInit(void){GPIO_InitTypeDef GPIO_InitStruct = {0};/* GPIO Ports Clock Enable */__HAL_RCC_GPIOA_CLK_ENABLE();/*Configure GPIO pin : PA1 */GPIO_InitStruct.Pin = LED_PIN;GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;GPIO_InitStruct.Pull = GPIO_PULLUP;GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;HAL_GPIO_Init(LED_PORT, &GPIO_InitStruct);}
在需要进入STOP模式的地方直接调用函数。
static void enter_stop_rtc_mode(void){//1. 配置stop之前各外设system_config_before_stop();//2.设置rtc唤醒时间20sstop_rtc_config(20);//3. 进入stopHAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);//3.退出stop后恢复时钟clock_config_after_stop();//4.恢复各外设gpioInit();}
对于低功耗产品开发，CPU的低功耗只是一部份，外围电路设计上也要综合考虑。目前测试到消耗电流比数据手册高。
附上工程代码，有需要的朋友可以参考。
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