Change_Interval.ino

/****************************************************************************************************************************
  Change_Interval.ino
  For SAMD boards
  Written by Khoi Hoang
  
  Built by Khoi Hoang https://github.com/khoih-prog/TimerInterrupt_Generic
  Licensed under MIT license
  
  Now even you use all these new 16 ISR-based timers,with their maximum interval practically unlimited (limited only by
  unsigned long miliseconds), you just consume only one SAMD timer and avoid conflicting with other cores' tasks.
  The accuracy is nearly perfect compared to software timers. The most important feature is they're ISR-based timers
  Therefore, their executions are not blocked by bad-behaving functions / tasks.
  This important feature is absolutely necessary for mission-critical tasks.
*****************************************************************************************************************************/

/*
   Notes:
   Special design is necessary to share data between interrupt code and the rest of your program.
   Variables usually need to be "volatile" types. Volatile tells the compiler to avoid optimizations that assume
   variable can not spontaneously change. Because your function may change variables while your program is using them,
   the compiler needs this hint. But volatile alone is often not enough.
   When accessing shared variables, usually interrupts must be disabled. Even with volatile,
   if the interrupt changes a multi-byte variable between a sequence of instructions, it can be read incorrectly.
   If your data is multiple variables, such as an array and a count, usually interrupts need to be disabled
   or the entire sequence of your code which accesses the data.
*/

#if !( defined(ARDUINO_SAMD_ZERO) || defined(ARDUINO_SAMD_MKR1000) || defined(ARDUINO_SAMD_MKRWIFI1010) \
      || defined(ARDUINO_SAMD_NANO_33_IOT) || defined(ARDUINO_SAMD_MKRFox1200) || defined(ARDUINO_SAMD_MKRWAN1300) || defined(ARDUINO_SAMD_MKRWAN1310) \
      || defined(ARDUINO_SAMD_MKRGSM1400) || defined(ARDUINO_SAMD_MKRNB1500) || defined(ARDUINO_SAMD_MKRVIDOR4000) \
      || defined(ARDUINO_SAMD_CIRCUITPLAYGROUND_EXPRESS) || defined(__SAMD51__) || defined(__SAMD51J20A__) \
      || defined(__SAMD51J19A__) || defined(__SAMD51G19A__) || defined(__SAMD51P19A__)  \
      || defined(__SAMD21E15A__) || defined(__SAMD21E16A__) || defined(__SAMD21E17A__) || defined(__SAMD21E18A__) \
      || defined(__SAMD21G15A__) || defined(__SAMD21G16A__) || defined(__SAMD21G17A__) || defined(__SAMD21G18A__) \
      || defined(__SAMD21J15A__) || defined(__SAMD21J16A__) || defined(__SAMD21J17A__) || defined(__SAMD21J18A__) )
  #error This code is designed to run on SAMD21/SAMD51 platform! Please check your Tools->Board setting.
#endif

/////////////////////////////////////////////////////////////////

// These define's must be placed at the beginning before #include "SAMDTimerInterrupt.h"
// _TIMERINTERRUPT_LOGLEVEL_ from 0 to 4
// Don't define _TIMERINTERRUPT_LOGLEVEL_ > 0. Only for special ISR debugging only. Can hang the system.
// Don't define TIMER_INTERRUPT_DEBUG > 2. Only for special ISR debugging only. Can hang the system.
#define TIMER_INTERRUPT_DEBUG         0
#define _TIMERINTERRUPT_LOGLEVEL_     0

// Select only one to be true for SAMD21. Must must be placed at the beginning before #include "SAMDTimerInterrupt.h"
// Depending on the board, you can select SAMD21 Hardware Timer from TC3, TC4, TC5, TCC, TCC1 or TCC2
// SAMD51 Hardware Timer has only TC3
#define USING_TIMER_TC3         true      // Only TC3 can be used for SAMD51
#define USING_TIMER_TC4         false     // Not to use with Servo library
#define USING_TIMER_TC5         false
#define USING_TIMER_TCC         false
#define USING_TIMER_TCC1        false
#define USING_TIMER_TCC2        false     // Don't use this, can crash on some boards

// Uncomment To test if conflict with Servo library
//#include "Servo.h"

/////////////////////////////////////////////////////////////////

// To be included only in main(), .ino with setup() to avoid `Multiple Definitions` Linker Error
#include "SAMDTimerInterrupt.h"

#ifndef LED_BUILTIN
  #define LED_BUILTIN       13
#endif

// TC3, TC4, TC5 max permissible TIMER_INTERVAL_MS is 1398.101 ms, larger will overflow, therefore not permitted
// Use TCC, TCC1, TCC2 for longer TIMER_INTERVAL_MS
#define TIMER_INTERVAL_MS        500

volatile uint32_t TimerCount = 0;

// Depending on the board, you can select SAMD21 Hardware Timer from TC3, TC4, TC5, TCC, TCC1 or TCC2
// SAMD51 Hardware Timer only TC3

#if (TIMER_INTERRUPT_USING_SAMD21)

  #if USING_TIMER_TC3
    #define SELECTED_TIMER      TIMER_TC3
  #elif USING_TIMER_TC4
    #define SELECTED_TIMER      TIMER_TC4
  #elif USING_TIMER_TC5
    #define SELECTED_TIMER      TIMER_TC5
  #elif USING_TIMER_TCC
    #define SELECTED_TIMER      TIMER_TCC
  #elif USING_TIMER_TCC1
    #define SELECTED_TIMER      TIMER_TCC1
  #elif USING_TIMER_TCC2
    #define SELECTED_TIMER      TIMER_TCC
  #else
    #error You have to select 1 Timer  
  #endif

#else

  #if !(USING_TIMER_TC3)
    #error You must select TC3 for SAMD51
  #endif
  
  #define SELECTED_TIMER      TIMER_TC3

#endif  

// Init selected SAMD timer
SAMDTimer ITimer(SELECTED_TIMER);

//////////////////////////////////////////////

void printResult(uint32_t currTime)
{
  Serial.print(F("Time = ")); Serial.print(currTime); 
  Serial.print(F(", TimerCount = ")); Serial.println(TimerCount);
}

//////////////////////////////////////////////

void TimerHandler()
{
  static bool toggle = false;

  // Flag for checking to be sure ISR is working as SErial.print is not OK here in ISR
  TimerCount++;

  //timer interrupt toggles pin LED_BUILTIN
  digitalWrite(LED_BUILTIN, toggle);
  toggle = !toggle;
}

//////////////////////////////////////////////

void setup()
{
  pinMode(LED_BUILTIN, OUTPUT);
  
  Serial.begin(115200);
  while (!Serial && millis() < 5000);

  delay(100);

  Serial.print(F("\nStarting Change_Interval on ")); Serial.println(BOARD_NAME);
  Serial.println(SAMD_TIMER_INTERRUPT_VERSION);
  Serial.print(F("CPU Frequency = ")); Serial.print(F_CPU / 1000000); Serial.println(F(" MHz"));
 
  // Interval in millisecs
  if (ITimer.attachInterruptInterval_MS(TIMER_INTERVAL_MS, TimerHandler))
  {
    Serial.print(F("Starting ITimer OK, millis() = ")); Serial.println(millis());
  }
  else
    Serial.println(F("Can't set ITimer. Select another freq. or timer"));
}

//////////////////////////////////////////////

#define CHECK_INTERVAL_MS     10000L
#define CHANGE_INTERVAL_MS    20000L

//////////////////////////////////////////////

void loop()
{
  static uint32_t lastTime = 0;
  static uint32_t lastChangeTime = 0;
  static uint32_t currTime;
  static uint32_t multFactor = 0;

  currTime = millis();

  if (currTime - lastTime > CHECK_INTERVAL_MS)
  {
    printResult(currTime);
    lastTime = currTime;

    if (currTime - lastChangeTime > CHANGE_INTERVAL_MS)
    {
      //setInterval(unsigned long interval, timerCallback callback)
      multFactor = (multFactor + 1) % 2;
      
      ITimer.setInterval_MS(TIMER_INTERVAL_MS * (multFactor + 1), TimerHandler);

       Serial.print(F("Changing Interval, Timer = ")); Serial.println(TIMER_INTERVAL_MS * (multFactor + 1));
      
      lastChangeTime = currTime;
    }
  }
}