说明：  在TMS320F28335中，利用ePWM控制ADC采样速率，转换完成，DMA控制器将数据从寄存器转移到内存中，并产生中断。
(On chip TMS320F28335, control the adc sampling rate by ePWM. when the conversion is complete, call the DMA controller to transfer the data into memory. After that, initiate an interrupt.)