STM32定时器慢2倍

Question

我使用的是STM32F042C4，我想设置以µs为单位的延迟计时器。但当我设置所有内容时，我会得到一个大2倍的。我正在寻找任何我可能错过的处方药，但我没有找到任何东西。

设置为：

//enable peripheral clock for TIM17
RCC->APB2ENR |= (0x1U << 18);
//Set HSI48 as clock source
while((RCC->CR2 >> 17) & 0x01U != 0x01U){      //wait for HSI48 ready
}
RCC->CR2 |= (0x1U << 16);                      //Enable HSI48
RCC->CFGR |= 0x00000003U;                      //Set HSI48 as clock source
//set TIM17 prescaler value for tick every 0,1 ms
TIM17->PSC = 4799;
//call delay func -> 10 000 should result in 1 sec delay, BUT I GET 2 SECONDS
void TIM17_delayUs(10000);
void TIM17_delayUs(uint16_t delay){
TIM17->CNT = 0x0U;                                      //null counter
TIM17->CR1 &= ~(0x1U << 7);                             //ARR buffer disable
TIM17->ARR = (48*delay)/(prescaler+1);                  //set delay
TIM17->CR1 |= (0x1U << 7);                              //ARR buffer enable
TIM17->CR1 |= (0x1U << 0);                              //enable counter
TIM17->ARR = 0xFFFFU;                                   //reset ARR
while((TIM17->SR & 0x1U) == 0){                         //wait for overflow event
}
TIM17->CR1 &= ~(0x1U << 0);                             //disable timer
TIM17->SR &= ~(0x1U << 0);                              //clear event flag
}

如果我查看寄存器，我可以看到AHB和APB预分频器是1，所以定时器的时钟源应该是48Mhz。在计时器之前，我看不到另一个预分频器，那么问题出在哪里呢？

STM32F442 的时钟图

TIM17 框图

Answer 1

我找不到错误。但是，如果prescaler的值是4799，那么TIM17->ARR = (48*delay)/(prescaler+1);行的求值结果为100，这似乎是错误的。

这段代码本可以用一种更简单的方式编写。代码越少，出错的可能性越低。忘记ARR，TIM启动&停止和中断标志。将ARR保持在最大值(0xffff，默认值(。换句话说，使TIM17成为一个自由运行的定时器，它总是启用的。

// TIM17 Settings
TIM17->PSC = 4799; // Set prescaler
TIM17->CR1 |= TIM_CR1_CEN; // Start timer
TIM17->EGR |= TIM_EGR_UG; // Generate update event for prescaler update
// Delay Function
delay100us(uint16_t us100) {
uint16_t start = TIM17->CNT;
while ((TIM17->CNT - start) < us100);
}