利用28335自带的ADC采集两路模拟正弦信号，用DMA方式将采样值写入内存，用epwm控制采样周期。利用FFT求得两路正弦信号的相位差。-Sampling two analog sinusoidal signals, write them to the memory by DMA controller. The sampling period is controlled by the EPWM module. Calculate the phase difference by FFT meth