/*
  LAB: 25
  Name: ESP32 Timer Interrupt Example
  Author: Khaled Magdy
  For More Info Visit: www.DeepBlueMbedded.com
  from https://deepbluembedded.com/esp32-timers-timer-interrupt-tutorial-arduino-ide/

  Adapted to modify the timer on the fly using hints from 
  https://espressif-docs.readthedocs-hosted.com/projects/arduino-esp32/en/latest/api/timer.html


*/

#define CLOCK_FREQ           (80000000L)
#define MAX_COUNTER          (0ULL -1)

#define VERBOSE 1

#define LED 21
hw_timer_t *Timer0_Cfg = NULL;

unsigned int step_loops;

void IRAM_ATTR Timer0_ISR()
{
  digitalWrite(LED, !digitalRead(LED));
}
void setup()
{
  Serial.begin(115200);
  pinMode(LED, OUTPUT);

  Timer0_Cfg = timerBegin(0, 80, true);
  timerAttachInterrupt(Timer0_Cfg, &Timer0_ISR, true);
  timerAlarmWrite(Timer0_Cfg, 8000000, true);
  timerAlarmEnable(Timer0_Cfg);

  timer_set_frequency(5);
}
void loop()
{
  modify_timer();
}

void modify_timer(void){
  static unsigned long last = 0;
  static float i = 1/3600.0/24/365/2;
  unsigned long now = millis();

  if (now - last < 2000 ) return; // too soon
  last = now;
  long n_freq = 1;
  i *= 3.0/2;
  timer_set_frequency(i);
  if(i > 150000){
    i = 1/3600.0/24/365;
  }
}

void timer_set_frequency(double desired_freq_hz) {
  // Source: http://letsmakerobots.com/node/28278
  // Different clock sources can be selected for each timer independently.
  // To calculate the timer frequency (for example 2Hz using timer1) you will need:

  step_loops = 1;

  // ESP32 64 bit, 80MHz timer per https://deepbluembedded.com/esp32-timers-timer-interrupt-tutorial-arduino-ide/
  //  TOUT = TimerTicks x (Prescaler/APB_CLK)
  //  FOUT = 1/TOUT = APB_CLK / prescaler / TimerTicks
  //  TimerTicks = APB_CLK / prescaler / FOUT
  //
  //  CPU frequency 16Mhz for Arduino
  //  maximum timer counter value (256 for 8bit, 65536 for 16bit timer)
  int prescaler_index = -1;
  int prescalers[] = {2, 8, 64, 256, 1024};
  unsigned long long counter_value = CLOCK_FREQ / 1ULL / desired_freq_hz;
  do {
   ++prescaler_index;
    //  Divide CPU frequency through the choosen prescaler (16000000 / 256 = 62500)
    counter_value = CLOCK_FREQ / prescalers[prescaler_index];
    //  Divide result through the desired frequency (62500 / 2Hz = 31250)
    counter_value /= desired_freq_hz;
    //  Verify counter_value < maximum timer. if fail, choose bigger prescaler.
  
  }   while (counter_value > MAX_COUNTER && prescaler_index < 4) ;

  if ( prescaler_index >= 5 ) {
    Serial.println(F("Timer could not be set: Desired frequency out of bounds."));
    return;
  }

#ifdef VERBOSE
  Serial.print(F("desired_freq_hz:"));  Serial.println(desired_freq_hz,8);
  Serial.print(F("counter_value:"));  Serial.print(counter_value);
  Serial.print(F(" counter_value%MAX:"));  Serial.print(100.0*counter_value/MAX_COUNTER,8);
  Serial.print(F(" prescaler_index:"));  Serial.print(prescaler_index);

  Serial.print(F(" = "));  Serial.print(((prescaler_index & 0x1)   ));
  Serial.print(F("/"));  Serial.print(((prescaler_index & 0x2) >> 1));
  Serial.print(F("/"));  Serial.println(((prescaler_index & 0x4) >> 2));
  Serial.print(F("prescaler:"));  Serial.println((prescalers[prescaler_index]));
  
#endif

  //Timer0_Cfg = timerBegin(0, prescalers[prescaler_index], true);
  //timerAttachInterrupt(Timer0_Cfg, &Timer0_ISR, true);
  timerAlarmWrite(Timer0_Cfg, counter_value, true);
  timerSetDivider(Timer0_Cfg,prescalers[prescaler_index]);
  //timerAlarmEnable(Timer0_Cfg);

  //timerWrite(Timer0_Cfg,counter_value);


  // // disable global interrupts
  // noInterrupts();

  // // set entire TCCR1A register to 0
  // TCCR1A = 0;
  // // set entire TCCR1B register to 0
  // TCCR1B = 0;
  // // set the overflow clock to 0
  // TCNT1  = 0;
  // // set compare match register to desired timer count
  // OCR1A = counter_value;
  // // turn on CTC mode
  // TCCR1B |= (1 << WGM12);
  // // Set CS10, CS11, and CS12 bits for prescaler
  // TCCR1B |= ( (( prescaler_index&0x1 )   ) << CS10);
  // TCCR1B |= ( (( prescaler_index&0x2 )>>1) << CS11);
  // TCCR1B |= ( (( prescaler_index&0x4 )>>2) << CS12);
  // // enable timer compare interrupt
  // TIMSK1 |= (1 << OCIE1A);

  //interrupts();  // enable global interrupts
}