请问PWM_EnablePeriodInt这函数的用法、里面参数个代表什么意思？

各位大大安安，想请问PWM_EnablePeriodInt这函数的用法，里面参数PWM_PERIOD_INT_UNDERFLOW和PWM_PERIOD_INT_MATCH_CNR各代表什么意思，谢谢!



/**

* @brief Enable period interrupt of selected channel

* @param[in] pwm The pointer of the specified PWM module

* @param[in] u32ChannelNum PWM channel number. Valid values are between 0~3

* @param[in] u32IntPeriodType Period interrupt type, could be either

*              - \ref PWM_PERIOD_INT_UNDERFLOW

*              - \ref PWM_PERIOD_INT_MATCH_CNR

* @return None

* @details This function is used to enable period interrupt of selected channel.

*          Every two channels, (0 & 1), (2 & 3), shares the period interrupt type setting.

*/

void PWM_EnablePeriodInt(PWM_T *pwm, uint32_t u32ChannelNum,  uint32_t u32IntPeriodType)

{

    (pwm)->PIER = ((pwm)->PIER & ~(PWM_PIER_INT01TYPE_Msk << (u32ChannelNum >> 1))) | \

                  (PWM_PIER_PWMIE0_Msk << u32ChannelNum) | (u32IntPeriodType << (u32ChannelNum >> 1));

}