5.2  看看Cube为我们做了哪些工作
  /* USER CODE BEGIN 1 */
  /* MCU Configuration----------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();//初始化了NVIC分组及SysTick

  /* Configure the system clock */
  SystemClock_Config();  //配置时钟、校准了MSI、使能了SysTick 的中断

  /* Initialize all configured peripherals */
  MX_GPIO_Init();//开了GPIOA、GPIOC的时钟
  MX_DMA_Init();//开DMA1时钟，设置DMA1 channel2的NVIC分组与使能
  MX_TIM2_Init();//TIM2的初始化，GPIO设置、PWM配置、DMA设置
/* USER CODE END 1 */

/**
  * @brief  Configure the Flash prefetch, the Instruction and Data caches,
  *         the time base source, NVIC and any required global low level hardware
  *         by calling the HAL_MspInit() callback function to be optionally defined in user file
  *         stm32l4xx_hal_msp.c.
  *
  * @note   HAL_Init() function is called at the beginning of program after reset and before
  *         the clock configuration.
  *            
  * @note   In the default implementation the System Timer (Systick) is used as source of time base.
  *         The Systick configuration is based on MSI clock, as MSI is the clock
  *         used after a system Reset and the NVIC configuration is set to Priority group 4.
  *         Once done, time base tick starts incrementing: the tick variable counter is incremented
  *         each 1ms in the SysTick_Handler() interrupt handler.
  *
  * @retval HAL status
  */
HAL_StatusTypeDef HAL_Init(void)
{
  /* Configure Flash prefetch, Instruction cache, Data cache */
  /* Default configuration at reset is:                      */
  /* - Prefetch disabled                                     */
  /* - Instruction cache enabled                             */
  /* - Data cache enabled                                    */
#if (INSTRUCTION_CACHE_ENABLE == 0)
   __HAL_FLASH_INSTRUCTION_CACHE_DISABLE();
#endif /* INSTRUCTION_CACHE_ENABLE */

#if (DATA_CACHE_ENABLE == 0)
   __HAL_FLASH_DATA_CACHE_DISABLE();
#endif /* DATA_CACHE_ENABLE */

#if (PREFETCH_ENABLE != 0)
  __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 MSI) */
  HAL_InitTick(TICK_INT_PRIORITY);

  /* Init the low level hardware */
  HAL_MspInit();

  /* Return function status */
  return HAL_OK;
}


/** System Clock Configuration
*/
void SystemClock_Config(void)
{

  RCC_OscInitTypeDef RCC_OscInitStruct;
  RCC_ClkInitTypeDef RCC_ClkInitStruct;

  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSE|RCC_OSCILLATORTYPE_MSI;
  RCC_OscInitStruct.LSEState = RCC_LSE_ON;
  RCC_OscInitStruct.MSIState = RCC_MSI_ON;
  RCC_OscInitStruct.MSICalibrationValue = 0;
  RCC_OscInitStruct.MSIClockRange = RCC_MSIRANGE_11;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  HAL_RCC_OscConfig(&RCC_OscInitStruct);

  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_MSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV8;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV8;
  HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2);

  __PWR_CLK_ENABLE();

  HAL_PWREx_ControlVoltageScaling(PWR_REGULATOR_VOLTAGE_SCALE1);

  HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);

  HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);

  HAL_RCCEx_EnableMSIPLLMode();

  /* SysTick_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
}


/** Configure pins as
        * Analog
        * Input
        * Output
        * EVENT_OUT
        * EXTI
*/
void MX_GPIO_Init(void)
{

  /* GPIO Ports Clock Enable */
  __GPIOC_CLK_ENABLE();
  __GPIOA_CLK_ENABLE();

}


/**
  * Enable DMA controller clock
  */
void MX_DMA_Init(void)
{
  /* DMA controller clock enable */
  __HAL_RCC_DMA1_CLK_ENABLE();

  /* DMA interrupt init */
  HAL_NVIC_SetPriority(DMA1_Channel2_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(DMA1_Channel2_IRQn);

}

/* TIM2 init function */
void MX_TIM2_Init(void)
{

  TIM_ClockConfigTypeDef sClockSourceConfig;
  TIM_MasterConfigTypeDef sMasterConfig;
  TIM_OC_InitTypeDef sConfigOC;

  htim2.Instance = TIM2;
  htim2.Init.Prescaler = 0;//时钟为总线时钟 12M，不分频
  htim2.Init.CounterMode = TIM_COUNTERMODE_UP;
  htim2.Init.Period = 1199;   //产生5Khz的PWM
  htim2.Init.ClockDivision = TIM_CLOCKDIVISION_DIV1;
  HAL_TIM_Base_Init(&htim2);    //下面有贴出此函数并对其调用函数分析与修改

  sClockSourceConfig.ClockSource = TIM_CLOCKSOURCE_INTERNAL;//没用，可注释掉
  HAL_TIM_ConfigClockSource(&htim2, &sClockSourceConfig);//没用，可注释掉

  HAL_TIM_PWM_Init(&htim2);//没用，可注释掉

  sMasterConfig.MasterOutputTrigger = TIM_TRGO_RESET;//没用，可注释掉
  sMasterConfig.MasterSlaveMode = TIM_MASTERSLAVEMODE_DISABLE;//没用，可注释掉
  HAL_TIMEx_MasterConfigSynchronization(&htim2, &sMasterConfig);//没用，可注释掉

  sConfigOC.OCMode = TIM_OCMODE_PWM1;
  sConfigOC.Pulse = 600;  //占空比为50%
  sConfigOC.OCPolarity = TIM_OCPOLARITY_HIGH;
  sConfigOC.OCFastMode = TIM_OCFAST_DISABLE;
  HAL_TIM_PWM_ConfigChannel(&htim2, &sConfigOC, TIM_CHANNEL_1);

}


/**
  * @brief  Initializes the TIM Time base Unit according to the specified
  *         parameters in the TIM_HandleTypeDef and initialize the associated handle.
  * @param  htim: TIM Base handle
  * @retval HAL status
  */
HAL_StatusTypeDef HAL_TIM_Base_Init(TIM_HandleTypeDef *htim)
{
  /* Check the TIM handle allocation */
  if(htim == NULL)
  {
    return HAL_ERROR;
  }

  /* Check the parameters */
  assert_param(IS_TIM_INSTANCE(htim->Instance));
  assert_param(IS_TIM_COUNTER_MODE(htim->Init.CounterMode));
  assert_param(IS_TIM_CLOCKDIVISION_DIV(htim->Init.ClockDivision));

  if(htim->State == HAL_TIM_STATE_RESET)
  {
    /* Allocate lock resource and initialize it */
    htim->Lock = HAL_UNLOCKED;

    /* Init the low level hardware : GPIO, CLOCK, NVIC */
    HAL_TIM_Base_MspInit(htim);//下面来看看这个函数
  }

  /* Set the TIM state */
  htim->State= HAL_TIM_STATE_BUSY;

  /* Set the Time Base configuration */
  TIM_Base_SetConfig(htim->Instance, &htim->Init);//此函数里有"Generate an update event to reload the Prescaler"

  /* Initialize the TIM state*/
  htim->State= HAL_TIM_STATE_READY;

  return HAL_OK;
}


void HAL_TIM_Base_MspInit(TIM_HandleTypeDef* htim_base)
{

  GPIO_InitTypeDef GPIO_InitStruct;
  if(htim_base->Instance==TIM2)
  {
  /* USER CODE BEGIN TIM2_MspInit 0 */

  /* USER CODE END TIM2_MspInit 0 */
    /* Peripheral clock enable */
    __TIM2_CLK_ENABLE();
  
    /**TIM2 GPIO Configuration   
    PA0     ------> TIM2_CH1
    */
    GPIO_InitStruct.Pin = GPIO_PIN_0;
    GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
    GPIO_InitStruct.Pull = GPIO_NOPULL;
    GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
    GPIO_InitStruct.Alternate = GPIO_AF1_TIM2;
    HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);

    /* Peripheral DMA init*/
  
    hdma_tim2_up.Instance = DMA1_Channel2;
    hdma_tim2_up.Init.Request = DMA_REQUEST_4;
    hdma_tim2_up.Init.Direction = DMA_MEMORY_TO_PERIPH;//在这里修改一下方向，生成的代码里为“DMA_PERIPH_TO_MEMORY”
    hdma_tim2_up.Init.PeriphInc = DMA_PINC_DISABLE;
    hdma_tim2_up.Init.MemInc = DMA_MINC_ENABLE;
    hdma_tim2_up.Init.PeriphDataAlignment = DMA_PDATAALIGN_WORD;//这里可根据寄存器情况修改为HALFWORD 或BYTE
    hdma_tim2_up.Init.MemDataAlignment = DMA_MDATAALIGN_WORD;//
    hdma_tim2_up.Init.Mode = DMA_NORMAL;
    hdma_tim2_up.Init.Priority = DMA_PRIORITY_LOW;
    HAL_DMA_Init(&hdma_tim2_up);

    __HAL_LINKDMA(htim_base,hdma[TIM_DMA_ID_UPDATE],hdma_tim2_up);

  /* USER CODE BEGIN TIM2_MspInit 1 */

  /* USER CODE END TIM2_MspInit 1 */
  }

}

5.3  需要另外做的工作
有空再写，睡觉了........