#include <avr/io.h>

void setup() {
  Serial.begin(9600);

  // init _everything_ since reprogramming != reset
  TCA0.SINGLE.CTRLA = 0;
  TCA0.SINGLE.CTRLB = 0;
  TCA0.SINGLE.CTRLC = 0;
  TCA0.SINGLE.CTRLD = 0;

  TCA0.SINGLE.PER = 1200; //pwm period
  TCA0.SINGLE.CMP2 = 650; //starting pulse width
  TCA0.SINGLE.CTRLB |= (1<<6); //enable compare TCA W02 (PB2)
  TCA0.SINGLE.CTRLB |= ((1<<0) | (1<<1)); //set TCA to single-slope PWM mode
  TCA0.SINGLE.CTRLA |= (1<<0); //enable timer TCA at clock speed
  PORTB.DIR |= (1<<2); 

  //TARE is on PB3, which is Digital 4 in Arduino-land.
  pinMode(4, INPUT_PULLUP);
 


}

void loop() {
  if (digitalRead(4) == HIGH) {
    TCA0.SINGLE.CMP2 = 1200;
  }
  else {
    TCA0.SINGLE.CMP2 = 650;
  }
}