检测方波周期，利用38035的捕获单元捕获PWM波的连续的俩个上升沿，两次捕获的时间差则为PWM波的周期。-Testing cycle square wave。Use 38035 PWM wave capture unit to capture both the continuous rising edge, the time difference was twice captured the cycle PWM wave.

2012电子设计 D题算法 基于到达时间差的平面声无源定位技术研究以及相关算法(2012 Electrical design algorithm of problem D)