//variables to keep track of the timing of recent interrupts
unsigned long trigger_time = 0;  
unsigned long last_trigger_time = 0;
unsigned long period = 100;
unsigned long idle = 1;
unsigned int rpm = 0;
const int pulsePerRev = 2;
float pulseDelay = 10; //degrees
float retard;
float usec_per_deg;
unsigned int fireFlag = 0;


void IRAM_ATTR isr() {
    trigger_time = millis();
		period = trigger_time - last_trigger_time;
    last_trigger_time = trigger_time;
		retard =  pulseDelay * usec_per_deg;
		retard =  2;
		while (millis() < trigger_time + retard){}
		digitalWrite(19, LOW);
		while (millis() < trigger_time + retard +1){}
}

void setup() {
	Serial.begin(115200);
	pinMode(18, INPUT_PULLUP);
	pinMode(19, OUTPUT);
	digitalWrite(19, HIGH);
  last_trigger_time = millis();
	attachInterrupt(18, isr, FALLING);
}

void loop() {
  rpm = 60000/(period*pulsePerRev);
	usec_per_deg = 1000000.*60./360./rpm;
	//Serial.printf("Period is %u msec\n", period);
  Serial.printf("RPM is %u \n", rpm);
	Serial.printf("usec/deg is %.1f \n", usec_per_deg);
	Serial.printf("retard is %f\n",retard);
	//printf("deg/usec is %.1 \n", deg_per_usec);

}