TimerInterruptTest.ino

/****************************************************************************************************************************
  TimerInterruptTest.ino
  For Teensy boards
  Written by Khoi Hoang
  
  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 Hardware 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.
  
  Based on SimpleTimer - A timer library for Arduino.
  Author: mromani@ottotecnica.com
  Copyright (c) 2010 OTTOTECNICA Italy
  
  Based on BlynkTimer.h
  Author: Volodymyr Shymanskyy
  
  Built by Khoi Hoang https://github.com/khoih-prog/TimerInterrupt_Generic
  Licensed under MIT license
*****************************************************************************************************************************/
/*
   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(CORE_TEENSY) || defined(TEENSYDUINO) )
  #error This code is designed to run on Teensy platform! Please check your Tools->Board setting.
#endif


// These define's must be placed at the beginning before #include "TimerInterrupt_Generic.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

#include "TimerInterrupt_Generic.h"

#ifndef LED_BUILTIN
  #define LED_BUILTIN       13
#endif

#ifndef LED_BLUE
  #define LED_BLUE          2
#endif

#ifndef LED_RED
  #define LED_RED           3
#endif

void TimerHandler0()
{
  static bool toggle0 = false;
  static bool started = false;

  if (!started)
  {
    started = true;
    pinMode(LED_BUILTIN, OUTPUT);
  }

#if (TIMER_INTERRUPT_DEBUG > 0)
  Serial.print("ITimer0: millis() = "); Serial.println(millis());
#endif

  //timer interrupt toggles pin LED_BUILTIN
  digitalWrite(LED_BUILTIN, toggle0);
  toggle0 = !toggle0;
}

// For Teensy 4.0/4.1, F_BUS_ACTUAL = 150 MHz => max period is only 55922 us (~17.9 Hz)
#define TIMER0_INTERVAL_MS        50L
#define TIMER0_DURATION_MS        5000L

// You can select Teensy Hardware Timer  from TEENSY_TIMER_1 or TEENSY_TIMER_3
// If using TEENSY_TIMER_3, the millis() can't be used.

// Init Teensy timer TEENSY_TIMER_1
TeensyTimer ITimer0(TEENSY_TIMER_1);

void setup()
{
  Serial.begin(115200);
  while (!Serial);
  
  delay(100);
  
  Serial.print(F("\nStarting TimerInterruptTest on ")); Serial.println(BOARD_NAME);
  Serial.println(TEENSY_TIMER_INTERRUPT_VERSION);
  Serial.println(TIMER_INTERRUPT_GENERIC_VERSION);
  Serial.print(F("CPU Frequency = ")); Serial.print(F_CPU / 1000000); Serial.println(F(" MHz"));

  // Interval in microsecs
  if (ITimer0.attachInterruptInterval(TIMER0_INTERVAL_MS * 1000, TimerHandler0))
  {
    Serial.print(F("Starting ITimer0 OK, millis() = ")); Serial.println(millis());
  }
  else
    Serial.println(F("Can't set ITimer0. Select another freq. or timer"));
}

void loop()
{
  static unsigned long lastTimer0   = 0;
  static bool timer0Stopped         = false;
  static unsigned long currTime     = 0;;

  currTime = millis();
   
  if (currTime - lastTimer0 > TIMER0_DURATION_MS)
  {
    lastTimer0 = currTime;

    if (timer0Stopped)
    {
      Serial.print(F("Start ITimer0, millis() = ")); Serial.println(currTime);
      ITimer0.restartTimer();
    }
    else
    {
      Serial.print(F("Stop ITimer0, millis() = ")); Serial.println(currTime);
      ITimer0.stopTimer();
    }
    timer0Stopped = !timer0Stopped;
  }
}