设置如下，EPWM2跟EPWM1设置是一样的
EPwm1Regs.AQCTLA.bit.CAU = 2;
EPwm1Regs.AQCTLA.bit.ZRO = 0;
EPwm1Regs.AQCTLA.bit.PRD = 1;
EPwm1Regs.AQCTLB.bit.CBU = 1;
EPwm1Regs.AQCTLB.bit.PRD = 2;
EPwm1Regs.AQCTLB.bit.ZRO = 0;
其中EPwm1Regs.TBPRD = 15000;占空比赋值：
EPwm1Regs.CMPA.half.CMPA = 4000;
EPwm1Regs.CMPB = 15000;
EPwm2Regs.CMPA.half.CMPA = 4000;
EPwm2Regs.CMPB = 15000;
EPwm3Regs.CMPA.half.CMPA = 4000;
EPwm3Regs.CMPB = 15000;
EPWM1A跟EPWM1B输出一样，EPWM2两个不一样，EPWM3两个不一样
如果按照下面赋值：
EPwm1Regs.CMPA.half.CMPA = 15000;
EPwm1Regs.CMPB = 4000;
EPWM1A跟EPWM1B输出又变成不一样的了
为什么呢？难道是28335坏了吗
