uint32_t ct;
uint32_t pre0;
uint32_t pre1;
uint16_t task0 = 20;
uint16_t task1 = 20;

void setup() {
  // put your setup code here, to run once:
  Serial1.begin(115200);
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  // analogReadResolution(12);
  analogWriteResolution(12);
  analogWriteFreq(500);

}

uint16_t duty0 = 0;
uint16_t duty1 = 0;
bool duty1up = 1;

void loop() {
  ct = millis();
  // sawtooth
  if(ct - pre0 >= task0) {
    pre0 = ct;
    duty0 += 70;
    if(duty0 >= 4000) duty0 = 0;
    analogWrite(2, duty0);
  }
  // triangle
  if(ct - pre1 >= task1) {
    Serial1.print(duty1up);
    Serial1.print(" : ");
    Serial1.println(duty1);
    pre1 = ct;
    if(duty1up == 1) {
      if(duty1 >= 4000) {
        duty1up = 0;
      } else {
        duty1 += 70;
      }
    } else {
      if(duty1 <= 50) {
        duty1up = 1;
      }
      else {
        duty1 -= 70;
      }
    }
    analogWrite(3, duty1);
  }
}