大佬们，求助

我想用STM32F103测一下一个方波的频率，结果一直在变。大佬们看一下程序对不对
uint16_t capture1 = 0;
uint16_t capture2 = 0;
uint16_t Capture_Result;
uint16_t captf;
uint16_t capture_number = 0;
uint16_t TIM3_Update_Cnt = 0;
char str[100] = {0};
char std[100] = {0};
void Timer3_Init(void)
{
TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
TIM_ICInitTypeDef TIM_ICInitStructure;
NVIC_InitTypeDef NVIC_InitStructure;
GPIO_InitTypeDef GPIO_InitStructure;
TIM_ClearITPendingBit(TIM4,TIM_IT_Update|TIM_IT_CC1);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_6;
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPU;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);
TIM_TimeBaseStructure.TIM_Period = 0xFFFF;
TIM_TimeBaseStructure.TIM_Prescaler = 1;
TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
TIM_TimeBaseInit(TIM3, &TIM_TimeBaseStructure);
TIM_ICStructInit(&TIM_ICInitStructure);
TIM_ICInitStructure.TIM_Channel = TIM_Channel_1;
TIM_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising;
TIM_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
TIM_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1;
TIM_ICInitStructure.TIM_ICFilter = 0x3;
TIM_ICInit(TIM3, &TIM_ICInitStructure);
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);
NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
TIM_Cmd(TIM3, ENABLE);
TIM_ITConfig(TIM3, TIM_IT_Update | TIM_IT_CC1, ENABLE);
TIM_ITConfig(TIM3, TIM_IT_CC1, ENABLE);
}
void TIM3_IRQHandler(void)
{
if(TIM_GetITStatus(TIM3, TIM_IT_Update) == SET)
{
TIM_ClearITPendingBit(TIM3, TIM_IT_Update);
TIM3_Update_Cnt++;
}
if(TIM_GetITStatus(TIM3, TIM_IT_CC1) == SET)
{
TIM_ClearITPendingBit(TIM3, TIM_IT_CC1);
if(capture_number == 0)
{
capture_number = 1;
capture1 = TIM_GetCapture1(TIM3);
}
else if(capture_number == 1)
{
capture2 = TIM_GetCapture1(TIM3);
if(capture2 >= capture1)
{
Capture_Result = (capture2 - capture1);
}
else if(capture2 < capture1)
{
Capture_Result = ((0xFFFF - capture1) + capture2);
}
else
{
Capture_Result = 0;
}
captf = (float)(SYSCLOCK_MY / 2) / Capture_Result
capture1 = capture2;
capture_number = 1;
}
Data = FreqToBit2(captf);
sprintf(str, "%d\t%d\r\n", captf, TIM3_Update_Cnt);
Usartl_SendString(str);
}
}