STM32F1Debug，定时器时基初始化参数

STM32F1，定时器时基初始化参数

错误代码：

在初始化时基时，没有给TIM_ClockDivision和TIM_RepetitionCounter赋值。

错误代码：

static void BSP_TIM_PWMOC_Config(void)
{
    uint16_t PSC = 7200;
    uint32_t ARR = 10000/20; 
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
    BSP_TIMx_PWMOC_Clk_Cmd(BSP_TIMx_PWMOC_Clk,ENABLE);
    
    TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInitStructure.TIM_Period= ARR-1;
    TIM_TimeBaseInitStructure.TIM_Prescaler = PSC-1;
    TIM_TimeBaseInit(BSP_TIMx_PWMOC,&TIM_TimeBaseInitStructure);
    TIM_ARRPreloadConfig(BSP_TIMx_PWMOC,ENABLE);
    
    TIM_OCInitTypeDef TIM_OCInitStructure;
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
	TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
	TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OCInitStructure.TIM_Pulse = ARR/2;
    TIM_OC1Init(BSP_TIMx_PWMOC,&TIM_OCInitStructure);
    TIM_OC1PreloadConfig(BSP_TIMx_PWMOC, TIM_OCPreload_Enable);
    TIM_Cmd(BSP_TIMx_PWMOC,ENABLE);
}

typedef struct
{
  uint16_t TIM_Prescaler;         /*!< Specifies the prescaler value used to divide the TIM clock.
                                       This parameter can be a number between 0x0000 and 0xFFFF */

  uint16_t TIM_CounterMode;       /*!< Specifies the counter mode.
                                       This parameter can be a value of @ref TIM_Counter_Mode */

  uint16_t TIM_Period;            /*!< Specifies the period value to be loaded into the active
                                       Auto-Reload Register at the next update event.
                                       This parameter must be a number between 0x0000 and 0xFFFF.  */ 

  uint16_t TIM_ClockDivision;     /*!< Specifies the clock division.
                                      This parameter can be a value of @ref TIM_Clock_Division_CKD */

  uint8_t TIM_RepetitionCounter;  /*!< Specifies the repetition counter value. Each time the RCR downcounter
                                       reaches zero, an update event is generated and counting restarts
                                       from the RCR value (N).
                                       This means in PWM mode that (N+1) corresponds to:
                                          - the number of PWM periods in edge-aligned mode
                                          - the number of half PWM period in center-aligned mode
                                       This parameter must be a number between 0x00 and 0xFF. 
                                       @note This parameter is valid only for TIM1 and TIM8. */
} TIM_TimeBaseInitTypeDef;       

当时考虑TIM_ClockDivision主要用于给死区时钟 ，也没有使用到TIM_RepetitionCounter，所以就没有给他们赋值。

预想输出：定时器输出PWM，20Hz，50%占空比。

实际输出：定时器输出PWM，10Hz，50%占空比。

错误分析：

经过debug发现：由于没有给参数赋值，结果MDK为局部变量产生一个随机值（但是每次debug都是这个值）。

可以看到此时

TIM_ClockDivision被赋值0x84D4,此时CR1被赋值为0xC4。

查STM32F1中文参考手册

可以发现CMS并没有被配置成边沿对齐模式，导致实际周期变为预计周期的一般。

修正错误

static void BSP_TIM_PWMOC_Config(void)
{
    uint16_t PSC = 7200;
    uint32_t ARR = 10000/20; 
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructure;
    BSP_TIMx_PWMOC_Clk_Cmd(BSP_TIMx_PWMOC_Clk,ENABLE);
    TIM_TimeBaseInitStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInitStructure.TIM_Period= ARR-1;
    TIM_TimeBaseInitStructure.TIM_Prescaler = PSC-1;
    TIM_TimeBaseInitStructure.TIM_RepetitionCounter = 0;
    TIM_TimeBaseInit(BSP_TIMx_PWMOC,&TIM_TimeBaseInitStructure);
    TIM_ARRPreloadConfig(BSP_TIMx_PWMOC,ENABLE);
    
    TIM_OCInitTypeDef TIM_OCInitStructure;
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
	TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
	TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OCInitStructure.TIM_Pulse = ARR/2;
    TIM_OC1Init(BSP_TIMx_PWMOC,&TIM_OCInitStructure);
    TIM_OC1PreloadConfig(BSP_TIMx_PWMOC, TIM_OCPreload_Enable);
    TIM_Cmd(BSP_TIMx_PWMOC,ENABLE);
}

此时CR1寄存器被正确配置。

结论

在C语言中变量都会默认初始化。其中全局变量会默认初始化为0，而局部变量会初始化随机值。
在使用外设的时候，还是要给参数初始化，以防出现未知错误。