配置定时100us的配置如下：

TIM_TimeBaseInitTypeDefTIM_TimeBaseStructure;

RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);

TIM_DeInit(TIM2);

TIM_TimeBaseStructure.TIM_Period=1;//59999;//1199;//9999;

TIM_TimeBaseStructure.TIM_CounterMode=TIM_CounterMode_Up;

TIM_TimeBaseStructure.TIM_ClockDivision=TIM_CKD_DIV1;

TIM_TimeBaseStructure.TIM_Prescaler=3499;//分频35999

TIM_TimeBaseInit(TIM2,&TIM_TimeBaseStructure);

TIM_ClearFlag(TIM2,TIM_IT_Update);

TIM_ITConfig(TIM2,TIM_IT_Update,ENABLE);

TIM_Cmd(TIM2,DISABLE);

//((1+TIM_Prescaler )/f_soc)*(1+TIM_Period )=((1+7199)/72M)*(1+9999)=1秒

time = ((1+3499)/72M)*(1+1) =100us ：f_soc =72MHz

看STM32的时钟树可以知道 Timer的f_soc= APB1_Clk * APB1_Prescaler

APB1_Clk = AHB_Clk /APB1_Prescaler

AHB_CLk = Sysclk /AHB_Prescaler

我这里的时钟设置 Sysclk = 72MHz

AHB_Prescaler = 1 => AHB_Clk = 72MHz

因为 APB1_CLK_max = 36MHz

所以 APB1_Prescaler =2

于是 Timer2 的f_soc = 72MHz