/* STM32 Blue Pill project using the STM32 Arduino Core (stm32duino) */

uint8_t TRG = PB12;
typedef unsigned long timestamp_t;
bool curTrg, lstTrg;
timestamp_t tmNow, tmPrev, tmPrev2, tmDiff;

bool chkTrg(){
  curTrg = digitalRead(TRG);
  //has it changed since last time?
  
    if(curTrg != lstTrg){
    //Serial.println(curTrg);
    if(!curTrg && lstTrg){
      lstTrg = curTrg;
      return true;
    }
  }
  lstTrg = curTrg;
  return false;
}
float RPM(){
  return ((60000000/tmDiff));
}
void setup() {
  Serial.begin(115200);
  pinMode(TRG, INPUT );
  //Serial.println("setup()");
}

void loop() {
  if(chkTrg()){
    tmNow = micros();
    tmDiff = (tmNow - tmPrev);
    if(tmPrev > 0){
      Serial.println(RPM());
      //Serial.println((1000000/tmDiff)*60 + "\n\n");
    }
    tmPrev = tmNow;
  }

}