1、功能说明
    1、TIM3 CH2引脚 CH2上升沿,CH1下降沿计算频率
2、使用环境
    软件开发环境：  KEIL MDK-ARM V5.26.2.0
    硬件环境：      基于N32L40XM-STB_V1.0开发
3、使用说明
    系统配置；
        1、时钟源：
            HSE=8M,PLL=64M,AHB=64M,APB1=16M,APB2=32M,TIM3 CLK=32M
        2、中断：
            TIM3 CH2上升沿 CH1下降沿中断打开，抢断优先级0，子优先级1
        3、端口配置：
            PA7选择为TIM3 CH2输入
            PA3选择为IO 输出
        4、TIM：
            TIM3 CH2上升沿，CH1下降沿捕获中断打开
    使用方法：
        1、编译后打开调试模式，连接PA3与PA7，将变量TIM3Freq添加到watch窗口
        2、程序控制PA3电平翻转后，查看TIM3Freq计算的频率值
4、注意事项
    无

1. Function description
     1. TIM3 CH2 pin CH2 rising edge, CH1 falling edge to calculate the frequency
2. Use environment
     Software development environment: KEIL MDK-ARM V5.26.2.0
     Hardware environment: Developed based on N32L40XM-STB_V1.0
3. Instructions for use
     System Configuration;
         1. Clock source:
             HSE=8M,PLL=64M,AHB=64M,APB1=16M,APB2=32M,TIM3 CLK=32M
         2. Interruption:
             TIM3 CH2 rising edge CH1 falling edge interrupt is turned on, preemption priority 0, sub priority 1
         3. Port configuration:
             PA7 is selected as TIM3 CH2 input
             PA3 is selected as IO output
         4. TIM:
             TIM3 CH2 rising edge, CH1 falling edge capture interrupt is turned on
     Instructions:
         1. After compiling, open the debug mode, connect PA3 and PA7, and add the variable TIM3Freq to the watch window
         2. After the program controls the level of PA3 to flip, check the frequency value calculated by TIM3Freq
4. Attention
     without