byte step = 0;
int duty = 100;
int accel = 1000;
int tarspeed = 3000;  // speed in eRPM (target)
int currspeed = 1; // current speed in eRPM
float castota = 0;  // in Hz
unsigned long tbstc = 10000; // time between step time changes
unsigned long cas = 0;
unsigned long past = 0;
unsigned long past2 = 0;
float cakaj = 0;  // time between steps

void setup() {

  TCCR2B = (TCCR2B & 0b11111000) | 0b00000001;
  TCCR1B = (TCCR1B & 0b11111000) | 0b00000001;

pinMode(9, OUTPUT);
pinMode(10, OUTPUT);
pinMode(11, OUTPUT);

Serial.begin(115200);
Serial.write(10);
Serial.write(10);
Serial.write(10);
Serial.write(10);
Serial.write(10);
Serial.write(10);
  tbstc = 1000000 / accel;
}

void loop() {
//yield();
cas = micros();

if(Serial.available() > 2) {
  tarspeed = Serial.parseInt();
  duty = Serial.parseInt();
  accel = Serial.parseInt();
  Serial.read();
  Serial.read();
  Serial.read();
  tbstc = 1000000 / accel;
}
if((currspeed < tarspeed) &&( cas - past2 > tbstc)) {
  currspeed = currspeed + 1;
  //Serial.println(castota);
  past2 = cas;
}

if(currspeed == tarspeed) {
  currspeed = tarspeed;
}

if((currspeed > tarspeed) &&( cas - past2 > tbstc)) {
  currspeed = currspeed - 1;
  past2 = cas;
}

castota = currspeed / 60.00;
cakaj = ((1000000 / castota) / 6);

if(cas - past >= cakaj) {
  //Serial.println(cas - past);
  step = step + 1;
  past = cas;
  }

switch(step) {

  case 0:
    analogWrite(9, duty);
    analogWrite(10, 0);
    analogWrite(11, 0);
    break;

  case 1:
    analogWrite(9, duty);
    analogWrite(10, duty);
    analogWrite(11, 0);
    break;

  case 2:
    analogWrite(9, 0);
    analogWrite(10, duty);
    analogWrite(11, 0);
    break;

  case 3:
    analogWrite(9, 0);
    analogWrite(10, duty);
    analogWrite(11, duty);
    break;

  case 4:
    analogWrite(9, 0);
    analogWrite(10, 0);
    analogWrite(11, duty);
    break;

  case 5:
    analogWrite(9, duty);
    analogWrite(10, 0);
    analogWrite(11, duty);
    break;

  case 6:
    step = 0;
    break;

} 

}