stm32 PWM counting mode

When PWM mode 1 is counting up, once TIMx_CNT<TIMx_CCR1, channel 1 is the active level, otherwise it is invalid. When counting down, once TIMx_CNT>TIMx_CCR1, channel 1 is the invalid level (OC1REF=0), otherwise it is Valid level (OC1REF=1). When PWM mode 2 is counting up, once TIMx_CNT<TIMx_CCR1, channel 1 is an invalid level, otherwise it is an active level. When counting down, once TIMx_CNT>TIMx_CCR1, channel 1 is an active level, otherwise it is an invalid level.