Use TCC1 timer generate PWM signal on personnal board

Question

I have a personal baord build with an samd21e18a and I use Arduino samd core. I'd like to generate PWM signal on PA30 if I look inside my variant.cpp I have this line for my pin

{ PORTA, 30, PIO_PWM, PIN_ATTR_DIGITAL|PIO_SERCOM, No_ADC_Channel, NOT_ON_PWM, TCC1_CH0, EXTERNAL_INT_10 }, // SWCLK

So for me I can use TCC1_CH0 so here is what I've tried

void setup() {

  GCLK->CLKCTRL.reg = GCLK_CLKCTRL_ID(TCC1_GCLK_ID) |
                    GCLK_CLKCTRL_GEN_GCLK0 |
                    GCLK_CLKCTRL_CLKEN;
                    
  while (GCLK->STATUS.bit.SYNCBUSY);

  Tcc* TC = (Tcc*) TCC1;
  TC->CTRLA.reg &= ~TCC_CTRLA_ENABLE; 


  TC->WAVE.reg = TCC_WAVE_WAVEGEN_NPWM; 

  TC->CTRLA.reg |= TCC_CTRLA_PRESCALER_DIV1 | 
                   TCC_CTRLA_RUNSTDBY;        


  PORT->Group[PORTA].PINCFG[30].bit.PMUXEN = 1; // activate alternate function
  PORT->Group[PORTA].PMUX[15].reg = PORT_PMUX_PMUXE_E; // use TCC1_CH0

  TC->CC[0].reg = 2000;     
  TC->CC[1].reg = 2500;  

  // Activer le timer
  TC->CTRLA.reg |= TCC_CTRLA_ENABLE;
  while (TC->SYNCBUSY.bit.ENABLE);

}

So if I plug my oscilloscope on my pin I have something but this is strange

If I change TC->CC[0].reg pulse width change but I don't understand why I have only one wave, it's the same if I change time measurement 40us to 2ms for example only one wave appear