2806x ePWM ETSEL中断触发问题

我想用28062的ePWM1事件触发ADC中断。

在调试时发现，ETSEL寄存器只有选择1（TBCTR=0）时，PWM按照给定频率触发。

当设置为TBCTR=2（TBCTR=TBPRD）或TBCTR=3（TBCTR=0或TBCTR=TBPRD）时，PWM触发周期出现抖动现象。

想请教这种情况发生的原因是什么？

EPwm1Regs.TBPRD = 2250;
EPwm1Regs.TBPHS.half.TBPHS = 0x0000;
EPwm1Regs.TBCTR = 0x0000;

EPwm1Regs.TBCTL.bit.CTRMODE = 0x2; //up-down-count mode
EPwm1Regs.TBCTL.bit.PHSEN =0x0;
EPwm1Regs.TBCTL.bit.HSPCLKDIV = 0x0; //high speed time-base clock prescale 0x0= /1
EPwm1Regs.TBCTL.bit.CLKDIV = 0x0; //time base clock prescale bit TBCLK = SYSCLKOUT/(HSPCLKDIV*CLKDIV)

EPwm1Regs.CMPCTL.bit.SHDWBMODE = 0x0;
EPwm1Regs.CMPCTL.bit.LOADBMODE = 0x1;

EPwm1Regs.AQCTLB.bit.CBU = 0x2;
EPwm1Regs.AQCTLB.bit.CBD = 0x1;

EPwm1Regs.ETSEL.bit.INTSEL = 0x1;
EPwm1Regs.ETSEL.bit.INTEN = 1;
EPwm1Regs.ETPS.bit.INTPRD = 0x1;