Is there a way to calculate -time interval- using Esp32 timers?

Question

I want to calculate time interval with timers. I'm using arduino ide. Also i can not decide which library to useful.

I just tried something following code.

I'm using this library

    #include <ESP32Time.h>

    int a;
    int b;
    int ldrValue;
    #define LDR 0

/* create a hardware timer */
 
      hw_timer_t * timer = NULL;

     int timeThatPast;

 /* motor pin */

      int motor = 14;

/* motor state */

     volatile byte state = LOW;
    
      void IRAM_ATTR onTimer(){
        state = !state;
        digitalWrite(motor, state);
    }

    void setup() {
      Serial.begin(115200);

      pinMode(motor, OUTPUT);

  /* Use 1st timer of 4 */
  /* 1 tick take 1/(80MHZ/80) = 1us so we set divider 80 and count up */
  
      timer = timerBegin(0, 80, false);

     /* Attach onTimer function to our timer */

      timerAttachInterrupt(timer, &onTimer, true);

//********************ALARM*******************
 

     /* Set alarm to call onTimer function every second 1 tick is 1us
      => 1 second is 1000000us */
      /* Repeat the alarm (third parameter) */
      timerAlarmWrite(timer, 7000000, false);

//********************************************
  /* Start an alarm */

      timerAlarmEnable(timer);
      Serial.println("start timer"); 

}

    void loop() {
      int ldrValue = analogRead(LDR);
      ldrValue = map(ldrValue, 0, 4095, 0, 10000);
        if(ldrValue > 8500){
           a = timerRead(timer);
          digitalWrite(motor,HIGH);
            while(1){
              int ldrValue = analogRead(LDR);
              ldrValue = map(ldrValue, 0, 4095, 0, 10000);
              
              if(ldrValue < 8500){
                
                b = timerRead(timer);
                digitalWrite(motor,LOW); 
                Serial.print("Entering Loop");
                Serial.println(a);
                Serial.println("**********");
                Serial.println("**********");
                Serial.print("Exiting loop");
                Serial.println(b);
                int difference = b - a;  
                Serial.println("Difference");       
                Serial.println(difference);
                break;     
              }

            }
          
          }
        
    }

Answer 1

Use millis or micros if you need more precise timing.

Here is an example sketch:

long lastDoTime = 0;

void setup(){
    Serial.begin(115200);
    delay(1000);
    Serial.println("Hello! We will do something at every ms");
}

void doThisAtEvery(int ms){
    if( millis() - lastDoTime >= ms ){
        // Must save the lastDoTime
        lastDoTime  = millis();

        // Do some stuff at every ms
    }
}

void loop(){
    // It will do the thing in every 100 ms.
    doThisAtEvery(100);
}

If you want to toggle a pin let's say every 100 microsec

long lastToggleTime = 0;
int motorPin = 14;
boolean lastPinState = LOW;

void setup(){
    Serial.begin(115200);
}

void togglePinEvery(int micros){
    if( micros() - lastToggleTime >= micros ){
        lastToggleTime = micros();
        digitalWrite(motorPin,!lastPinState);
        lastPinState = !lastPinState;
    }
}

void loop(){
    togglePinEvery(100);
}

EDIT Since you wanted timers only.

Here is a detailed explanation about timers: https://techtutorialsx.com/2017/10/07/esp32-arduino-timer-interrupts/

Code example:

volatile int interruptCounter;
int totalInterruptCounter;
 
hw_timer_t * timer = NULL;
portMUX_TYPE timerMux = portMUX_INITIALIZER_UNLOCKED;
 
void IRAM_ATTR onTimer() {
  portENTER_CRITICAL_ISR(&timerMux);
  interruptCounter++;
  portEXIT_CRITICAL_ISR(&timerMux);
 
}
 
void setup() {
 
  Serial.begin(115200);
 
  timer = timerBegin(0, 80, true);
  timerAttachInterrupt(timer, &onTimer, true);
  timerAlarmWrite(timer, 1000000, true);
  timerAlarmEnable(timer);
 
}
 
void loop() {
 
  if (interruptCounter > 0) {
 
    portENTER_CRITICAL(&timerMux);
    interruptCounter--;
    portEXIT_CRITICAL(&timerMux);
 
    totalInterruptCounter++;
 
    Serial.print("An interrupt as occurred. Total number: ");
    Serial.println(totalInterruptCounter);
 
  }
}