int pin_gate = 2;//gate输入
int pin_out = 8;//方波输出
int bpm = 60;
int beatUp = 4;//拍号分母
int pin_root = A0;
int pin_bpm = A1;
int pin_apply = 1;

#include <TimerOne.h>
#include <math.h>

int duration = 0;

bool gate = false;

int arps[] = {0,1,2,3};
int arpPos = 0;
int root = 59;

void noteOn(){
  arpPos = 0;
  gate = true;
}

void noteOff(){
  gate = false;
}

void onChange(){
  if(gate){
    noteOff();
    return;
  }
  noteOn();
}

void updateP(){
  bpm = map(analogRead(pin_bpm),0,1023,20,999);
  Timer1.initialize(60000000/bpm/beatUp);
}

void arpLoop(){
  if(!gate) return;

  int note = arps[arpPos] + root;
  auto fre = 1.f*powf(2.f,(note-59)/12.f);
  duration = int(1000000.f/fre);
  duration = duration < 0?0:duration ;
  duration = duration > 65535?65535:duration;

  digitalWrite(7,arpPos&0x2);
  digitalWrite(6,arpPos&0x1);

  ++arpPos;
  arpPos &= 3;
}

void setup() {
  Serial.begin(9600);
  // put your setup code here, to run once:
  pinMode(pin_gate, INPUT);
  pinMode(pin_out, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(pin_bpm, INPUT);//bpm在这个定时器用不了
  pinMode(pin_root, INPUT);
  pinMode(pin_apply, INPUT);

  attachInterrupt(digitalPinToInterrupt(pin_gate), onChange,CHANGE  );
  attachInterrupt(digitalPinToInterrupt(pin_apply), updateP ,CHANGE   );
  Timer1.initialize(60000000/bpm/beatUp);
  Timer1.attachInterrupt(arpLoop);
}

void loop() {
  // put your main code here, to run repeatedly:

  root = map(analogRead(pin_root),0,1023,0,100);

  if(!gate) return;

  digitalWrite(pin_out, HIGH);
  delayMicroseconds(duration);
  digitalWrite(pin_out, LOW);
  delayMicroseconds(duration);
}