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1.1 简介
SysTick#xff1a;系统滴答时钟#xff0c;属于Cortex-M4内核中的一个外设#xff0c;24bit向下递减计数。 Systick定时器常用来做延时#xff0c;… STM32 系统滴答时钟启动过程 SysTick_Config 1. 系统滴答时钟1.1 简介1.2 配置1.3 启动和更新 1. 系统滴答时钟
1.1 简介
SysTick系统滴答时钟属于Cortex-M4内核中的一个外设24bit向下递减计数。 Systick定时器常用来做延时或者实时系统的心跳时钟。这样可以节省MCU资源不用浪费一个定时器。比如UCOS中分时复用需要一个最小的时间戳一般在STM32UCOS系统中都采用Systick做UCOS心跳时钟
1.2 配置
用STM32CubeMX配置时钟树时可以看到Cortex system timer就是滴答时钟
1.3 启动和更新
在STM32CubeMX生成的工程中滴答时钟启动过程如下
HAL_Init() 初始化时:SystemCoreClock 16000000, HAL_InitTick HAL_SYSTICK_Config(SystemCoreClock / (1000U / uwTickFreq)) SysTick_Config() SystemCoreClock is updated in three ways: 1) by calling CMSIS function SystemCoreClockUpdate() 2) by calling HAL API function HAL_RCC_GetHCLKFreq() 3) each time HAL_RCC_ClockConfig() is called to configure the system clock frequency
//main()函数启动
/* Reset of all peripherals, Initializes the Flash interface and the Systick. */HAL_Init();//stm32f4xx_hal.c
HAL_StatusTypeDef HAL_Init(void)
{/* Configure Flash prefetch, Instruction cache, Data cache */
#if (INSTRUCTION_CACHE_ENABLE ! 0U)__HAL_FLASH_INSTRUCTION_CACHE_ENABLE();
#endif /* INSTRUCTION_CACHE_ENABLE */#if (DATA_CACHE_ENABLE ! 0U)__HAL_FLASH_DATA_CACHE_ENABLE();
#endif /* DATA_CACHE_ENABLE */#if (PREFETCH_ENABLE ! 0U)__HAL_FLASH_PREFETCH_BUFFER_ENABLE();
#endif /* PREFETCH_ENABLE *//* Set Interrupt Group Priority */HAL_NVIC_SetPriorityGrouping(NVIC_PRIORITYGROUP_4);/* Use systick as time base source and configure 1ms tick (default clock after Reset is HSI) */HAL_InitTick(TICK_INT_PRIORITY);/* Init the low level hardware */HAL_MspInit();/* Return function status */return HAL_OK;
}//stm32f4xx_hal.c
__weak HAL_StatusTypeDef HAL_InitTick(uint32_t TickPriority)
{/* Configure the SysTick to have interrupt in 1ms time basis*/if (HAL_SYSTICK_Config(SystemCoreClock / (1000U / uwTickFreq)) 0U){return HAL_ERROR;}/* Configure the SysTick IRQ priority */if (TickPriority (1UL __NVIC_PRIO_BITS)){HAL_NVIC_SetPriority(SysTick_IRQn, TickPriority, 0U);uwTickPrio TickPriority;}else{return HAL_ERROR;}/* Return function status */return HAL_OK;
}// stm32f4xx_hal_cortex.c
uint32_t HAL_SYSTICK_Config(uint32_t TicksNumb)
{return SysTick_Config(TicksNumb);
}// core_cm4.h
__STATIC_INLINE uint32_t SysTick_Config(uint32_t ticks)
{if ((ticks - 1UL) SysTick_LOAD_RELOAD_Msk){return (1UL); /* Reload value impossible */}SysTick-LOAD (uint32_t)(ticks - 1UL); /* set reload register */NVIC_SetPriority (SysTick_IRQn, (1UL __NVIC_PRIO_BITS) - 1UL); /* set Priority for Systick Interrupt */SysTick-VAL 0UL; /* Load the SysTick Counter Value */SysTick-CTRL SysTick_CTRL_CLKSOURCE_Msk |SysTick_CTRL_TICKINT_Msk |SysTick_CTRL_ENABLE_Msk; /* Enable SysTick IRQ and SysTick Timer */return (0UL); /* Function successful */
}SystemClock_Config() 时调用HAL_RCC_ClockConfig()对系统SystemCoreClock更新
SystemClock_Config(); SystemCoreClock HAL_RCC_GetSysClockFreq() AHBPrescTable[(RCC-CFGR RCC_CFGR_HPRE) RCC_CFGR_HPRE_Pos];HAL_InitTick (uwTickPrio);
// main()
/* Configure the system clock */SystemClock_Config();void SystemClock_Config(void)
{RCC_OscInitTypeDef RCC_OscInitStruct {0};RCC_ClkInitTypeDef RCC_ClkInitStruct {0};/** Configure the main internal regulator output voltage*/__HAL_RCC_PWR_CLK_ENABLE();__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);/** Initializes the RCC Oscillators according to the specified parameters* in the RCC_OscInitTypeDef structure.*/RCC_OscInitStruct.OscillatorType RCC_OSCILLATORTYPE_HSE;RCC_OscInitStruct.HSEState RCC_HSE_ON;RCC_OscInitStruct.PLL.PLLState RCC_PLL_ON;RCC_OscInitStruct.PLL.PLLSource RCC_PLLSOURCE_HSE;RCC_OscInitStruct.PLL.PLLM 8;RCC_OscInitStruct.PLL.PLLN 336;RCC_OscInitStruct.PLL.PLLP RCC_PLLP_DIV2;RCC_OscInitStruct.PLL.PLLQ 4;if (HAL_RCC_OscConfig(RCC_OscInitStruct) ! HAL_OK){Error_Handler();}/** Initializes the CPU, AHB and APB buses clocks*/RCC_ClkInitStruct.ClockType RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK|RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;RCC_ClkInitStruct.SYSCLKSource RCC_SYSCLKSOURCE_PLLCLK;RCC_ClkInitStruct.AHBCLKDivider RCC_SYSCLK_DIV1;RCC_ClkInitStruct.APB1CLKDivider RCC_HCLK_DIV4;RCC_ClkInitStruct.APB2CLKDivider RCC_HCLK_DIV2;if (HAL_RCC_ClockConfig(RCC_ClkInitStruct, FLASH_LATENCY_5) ! HAL_OK){Error_Handler();}
}// stm32f4xx_hal_rcc.c
HAL_RCC_ClockConfig()
{
HAL_InitTick (uwTickPrio);
}在中断中更新时钟计数
// stm32f4xx_it.c
void SysTick_Handler(void)
{/* USER CODE BEGIN SysTick_IRQn 0 *//* USER CODE END SysTick_IRQn 0 */HAL_IncTick();/* USER CODE BEGIN SysTick_IRQn 1 *//* USER CODE END SysTick_IRQn 1 */
}// stm32f4xx_hal.c
__weak void HAL_IncTick(void)
{uwTick uwTickFreq;
}参考
STM32入门Systick嘀嗒定时器学习stm32f4xx-systick系统滴答时钟
