PMSM3-3例程，Enable CNT_zero interrupt using EPWM1 Time-base是什么意思

大家好，

// Enable CNT_zero interrupt using EPWM1 Time-base
EPwm1Regs.ETSEL.bit.INTEN = 1; // Enable EPWM1INT generation
EPwm1Regs.ETSEL.bit.INTSEL = 1; // Enable interrupt CNT_zero event
EPwm1Regs.ETPS.bit.INTPRD = 1; // Generate interrupt on the 1st event
EPwm1Regs.ETCLR.bit.INT = 1; // Enable more interrupts

还有下面的主中断程序是怎么进入的？

// Enable PIE group 3 interrupt 1 for EPWM1_INT
PieCtrlRegs.PIEIER3.all = M_INT1;

// Enable CPU INT3 for EPWM1_INT:
IER |= M_INT3;

这应该是中断使能吧。但是中断是怎么触发的呢？？？？

interrupt void MainISR(void)

怎么触发这个主中断？？？？

谢谢各位了。