68.6.6.1 External PWM Reset Mode
External PWM Reset mode is selected by programming TRGMODE = 1 in the PWM_ETRGx register.
In this mode, when an edge is detected on the PWMEXTRGx input, the internal PWM counter is cleared and a new PWM cycle is restarted. The edge polarity can be selected by programming the TRGEDGE bit in the PWM_ETRGx register. If no trigger event is detected when the internal channel counter has reached the CPRD value in the PWM Channel Period Register, the internal counter is cleared and a new PWM cycle starts.
Note that this mode does not ensure a constant tON or tOFF time.
