时钟系统与定时器

关键概念

STM32F4 时钟树图解

时钟配置代码（STM32CubeMX 生成）

/**
 * @brief 系统时钟配置：HSE 8MHz → PLL → SYSCLK 168MHz
 *        这段代码通常由 CubeMX 自动生成，了解参数含义很重要
 */
void SystemClock_Config(void) {
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};

  /* 使能电源控制时钟，并设置 VOS = Scale1（最高性能） */
  __HAL_RCC_PWR_CLK_ENABLE();
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);

  /* ① 配置 HSE + PLL */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
  RCC_OscInitStruct.HSEState       = RCC_HSE_ON;     /* 开启 HSE */
  RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_ON;
  RCC_OscInitStruct.PLL.PLLSource  = RCC_PLLSOURCE_HSE;
  RCC_OscInitStruct.PLL.PLLM = 8;    /* HSE/8 = 1MHz 进 VCO */
  RCC_OscInitStruct.PLL.PLLN = 336;  /* VCO = 1×336 = 336MHz */
  RCC_OscInitStruct.PLL.PLLP = RCC_PLLP_DIV2;  /* SYSCLK = 336/2 = 168MHz */
  RCC_OscInitStruct.PLL.PLLQ = 7;    /* USB = 336/7 = 48MHz */
  HAL_RCC_OscConfig(&RCC_OscInitStruct);

  /* ② 配置总线分频 */
  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;    /* HCLK = 168MHz */
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV4;      /* APB1 = 42MHz */
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV2;      /* APB2 = 84MHz */
  /* Flash 延迟：168MHz 时需要 5 等待周期 */
  HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5);
}

SysTick 定时器原理

通用定时器 PWM 输出

用 TIM3 CH1（PA6）输出 1kHz PWM，初始占空比 50%，然后通过修改 CCR 值改变亮度：

/**
 * @brief TIM3 CH1 PWM 初始化
 *        引脚: PA6（AF2 = TIM3_CH1）
 *        TIM3 挂在 APB1，时钟 = 84MHz
 *        PWM 频率 = 84MHz / (PSC+1) / (ARR+1) = 84M/84/1000 = 1kHz
 */
TIM_HandleTypeDef htim3;

void TIM3_PWM_Init(void) {
  TIM_OC_InitTypeDef sConfigOC = {0};

  /* 开启时钟 */
  __HAL_RCC_TIM3_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();

  /* 配置 PA6 为 TIM3_CH1 复用推挽输出 */
  GPIO_InitTypeDef GPIO_InitStruct = {0};
  GPIO_InitStruct.Pin       = GPIO_PIN_6;
  GPIO_InitStruct.Mode      = GPIO_MODE_AF_PP;     /* 复用推挽 */
  GPIO_InitStruct.Pull      = GPIO_NOPULL;
  GPIO_InitStruct.Speed     = GPIO_SPEED_FREQ_HIGH;
  GPIO_InitStruct.Alternate = GPIO_AF2_TIM3;       /* TIM3 是 AF2 */
  HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

  /* 配置定时器基参数 */
  htim3.Instance               = TIM3;
  htim3.Init.Prescaler         = 84 - 1;    /* 84MHz/84 = 1MHz 计数时钟 */
  htim3.Init.CounterMode       = TIM_COUNTERMODE_UP;
  htim3.Init.Period            = 1000 - 1;  /* ARR=999, 1MHz/1000 = 1kHz PWM */
  htim3.Init.ClockDivision     = TIM_CLOCKDIVISION_DIV1;
  htim3.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_ENABLE;
  HAL_TIM_PWM_Init(&htim3);

  /* 配置 PWM 通道1 */
  sConfigOC.OCMode       = TIM_OCMODE_PWM1;   /* CNT
  sConfigOC.Pulse        = 500;              /* CCR=500 → 50% 占空比 */
  sConfigOC.OCPolarity   = TIM_OCPOLARITY_HIGH;
  sConfigOC.OCFastMode   = TIM_OCFAST_DISABLE;
  HAL_TIM_PWM_ConfigChannel(&htim3, &sConfigOC, TIM_CHANNEL_1);

  /* 启动 PWM 输出 */
  HAL_TIM_PWM_Start(&htim3, TIM_CHANNEL_1);
}

/**
 * @brief 动态改变 PWM 占空比（0-100）
 *        在运行时直接修改 CCR 寄存器即可，无需重新初始化
 */
void PWM_SetDuty(uint8_t duty_percent) {
  uint32_t pulse = ((uint32_t)duty_percent * (__HAL_TIM_GET_AUTORELOAD(&htim3) + 1)) / 100;
  __HAL_TIM_SET_COMPARE(&htim3, TIM_CHANNEL_1, pulse);
  /* 也可直接写寄存器：TIM3->CCR1 = pulse; */
}

输入捕获测量脉宽

/* 用 TIM2 CH1（PA0）输入捕获，测量 HC-SR04 超声波 Echo 脉宽 */
TIM_HandleTypeDef htim2;
volatile uint32_t ic_val1 = 0, ic_val2 = 0;
volatile uint8_t  ic_done = 0;

void TIM2_IC_Init(void) {
  TIM_IC_InitTypeDef sConfigIC = {0};
  __HAL_RCC_TIM2_CLK_ENABLE();

  htim2.Instance               = TIM2;
  htim2.Init.Prescaler         = 84 - 1;   /* 1MHz 计数 */
  htim2.Init.CounterMode       = TIM_COUNTERMODE_UP;
  htim2.Init.Period            = 0xFFFFFFFF; /* TIM2 是32位，不溢出 */
  HAL_TIM_IC_Init(&htim2);

  sConfigIC.ICPolarity  = TIM_ICPOLARITY_BOTHEDGE;  /* 双边沿都捕获 */
  sConfigIC.ICSelection = TIM_ICSELECTION_DIRECTTI;
  sConfigIC.ICPrescaler = TIM_ICPSC_DIV1;
  sConfigIC.ICFilter    = 0;
  HAL_TIM_IC_ConfigChannel(&htim2, &sConfigIC, TIM_CHANNEL_1);
  HAL_TIM_IC_Start_IT(&htim2, TIM_CHANNEL_1);  /* 中断模式 */
}

/* 捕获中断回调 */
void HAL_TIM_IC_CaptureCallback(TIM_HandleTypeDef *htim) {
  static uint8_t edge = 0;
  if (htim->Instance == TIM2) {
    if (!edge) {
      ic_val1 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1);
      edge = 1;
    } else {
      ic_val2 = HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1);
      edge = 0; ic_done = 1;
    }
  }
}

/* 计算距离：脉宽(μs) / 58 = 距离(cm) */
float HCSR04_GetDistance_cm(void) {
  ic_done = 0;
  uint32_t timeout = HAL_GetTick() + 100;
  while (!ic_done && HAL_GetTick() < timeout);
  if (!ic_done) return -1.0f;  /* 超时 */
  uint32_t pulse_us = ic_val2 - ic_val1;
  return pulse_us / 58.0f;
}