工程文件名：TIM_TimeBase
代码段：
PrescalerValue = (uint16_t) ((SystemCoreClock / 2) / 500000) - 1;
/* Time base configuration */
TIM_TimeBaseStructure.TIM_Period = 65535;
TIM_TimeBaseStructure.TIM_Prescaler = 0;
TIM_TimeBaseStructure.TIM_ClockDivision = 0;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
/* Prescaler configuration */
TIM_PrescalerConfig(TIM3, PrescalerValue, TIM_PSCReloadMode_Immediate);
问什么向把预分频值设置成0再用TIM_PrescalerConfig(TIM3, PrescalerValue, TIM_PSCReloadMode_Immediate);函数配置预分频值呢？
经过通过网络搜索答案如下：
原来PSC也有个预装载功能，却不像ARR和CRR那样有相关的位控制立即装载或更新事件装载。也就是说只能更新事件来装载。在上面函数中手工产生了一个更新事件，使PSC立刻生效。
但是我发现
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);函数里已经用到了
/* Generate an update event to reload the Prescaler
and the repetition counter(only for TIM1 and TIM8) value immediatly */
TIMx->EGR = TIM_PSCReloadMode_Immediate; 通过设置EGR位产生更新事件已经将预分频值装置到影子寄存器了
何必将预分频值先写为0再通过TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);函数在配置呢？
两个配置函数如下：
void TIM_TimeBaseInit(TIM_TypeDef* TIMx, TIM_TimeBaseInitTypeDef* TIM_TimeBaseInitStruct)
{
uint16_t tmpcr1 = 0;
/* Check the parameters */
assert_param(IS_TIM_ALL_PERIPH(TIMx));
assert_param(IS_TIM_COUNTER_MODE(TIM_TimeBaseInitStruct->TIM_CounterMode));
assert_param(IS_TIM_CKD_DIV(TIM_TimeBaseInitStruct->TIM_ClockDivision));
tmpcr1 = TIMx->CR1;
if((TIMx == TIM1) || (TIMx == TIM8)||
(TIMx == TIM2) || (TIMx == TIM3)||
(TIMx == TIM4) || (TIMx == TIM5))
{
/* Select the Counter Mode */
tmpcr1 &= (uint16_t)(~(TIM_CR1_DIR | TIM_CR1_CMS));
tmpcr1 |= (uint32_t)TIM_TimeBaseInitStruct->TIM_CounterMode;
}
if((TIMx != TIM6) && (TIMx != TIM7))
{
/* Set the clock division */
tmpcr1 &= (uint16_t)(~TIM_CR1_CKD);
tmpcr1 |= (uint32_t)TIM_TimeBaseInitStruct->TIM_ClockDivision;
}
TIMx->CR1 = tmpcr1;
/* Set the Autoreload value */
TIMx->ARR = TIM_TimeBaseInitStruct->TIM_Period ;
/* Set the Prescaler value */
TIMx->PSC = TIM_TimeBaseInitStruct->TIM_Prescaler;
if ((TIMx == TIM1) || (TIMx == TIM8))
{
/* Set the Repetition Counter value */
TIMx->RCR = TIM_TimeBaseInitStruct->TIM_RepetitionCounter;
}
/* Generate an update event to reload the Prescaler
and the repetition counter(only for TIM1 and TIM8) value immediatly */
TIMx->EGR = TIM_PSCReloadMode_Immediate;
}
void TIM_PrescalerConfig(TIM_TypeDef* TIMx, uint16_t Prescaler, uint16_t TIM_PSCReloadMode)
{
/* Check the parameters */
assert_param(IS_TIM_ALL_PERIPH(TIMx));
assert_param(IS_TIM_PRESCALER_RELOAD(TIM_PSCReloadMode));
/* Set the Prescaler value */
TIMx->PSC = Prescaler;
/* Set or reset the UG Bit */
TIMx->EGR = TIM_PSCReloadMode;
}
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