Arduino 101 Curie Timer One Interrupt

With this tutorial you learn to use one of the timers available in the microcontroller. The library uses Timer 1 and this tutorial shows how to set up an interrupt at variable intervals to toggle the on-board LED. The interrupt is the only way to exit from a delay() function and it is used in this sketch to show how a delay instruction - that apparently stops the flow of the code execution - is temporarily exited to toggle the LED, then it is continued from where it was interrupted. The final effect is a 10 seconds blinking block with the same blinking rate, incremented every 10 seconds in four steps.

Hardware Required

Arduino 101

The Circuit

genuino101fzz

image developed using Fritzing. No additional hardware is needed to use this tutorial.

Software Essentials

Libraries

CurieTimerOne.h is the library that provides access to the Timer 1 of the microcontroller. This library allows to set up the number of microseconds that the timer counts before it asserts an interrupt. The interrupt can be configured to call a specific function - the callback function - and each interrupt increments a counter. The same library is used to generate a PWM signal with duty cycle and period lenght fully customizable.

Functions

timedBlinkIsr() - is the function to which the sketch execution is passed when the interrupt is asserted. It toggles the state of the LED on D13 using the toggle variable that is changed using the "!" (NOT) operator at each call.

Code

The code is written with a serial monitor feature that can be toggled commenting or uncommenting #define SERIAL_PORT_LOG_ENABLE 1.

/*

  Sketch: Timer1Interrupt.ino

  This sketch demonstrates the usage of the Curie Timer One Library.

  It uses timer-1 to blink the onboard LED, pin 13, at different

  intervals (speed) in four steps.

  You can see the time interval and the number of interrupt counted

  in 10 seconds if you keep serial logging active, but this may require

  a MASTER_RESET to reprogram the board.

  Blinking of the LED will start only when you open the  Serial Monitor

  unless you comment the "#define SERIAL_PORT_LOG_ENABLE 1"; don't

  forget to uncomment "CurieTimerOne.restart(time);"

  created by Intel

  Modified 14 March 2016

  by Simone Majocchi

  This example code is in the public domain.

*/

#include "CurieTimerOne.h"

// Comment the following statement to disable logging on serial port.
#define SERIAL_PORT_LOG_ENABLE 1

const int oneSecInUsec = 1000000;   // A second in mirco second unit.

bool toggle = 0;                    // The LED status toggle
int time;                           // the variable used to set the Timer

void timedBlinkIsr()   // callback function when interrupt is asserted
{

  digitalWrite(13, toggle);

  toggle = !toggle;  // use NOT operator to invert toggle value
}

void setup() {

#ifdef SERIAL_PORT_LOG_ENABLE

  Serial.begin(115200);  //  initialize Serial communication

  while (!Serial);       //  wait for the serial monitor to open
#endif

  // Initialize pin 13 as an output - onboard LED.

  pinMode(13, OUTPUT);
}

void loop() {

  for (int i = 1; i < 9; i = i * 2) {

    // We set a blink rate of 1000000, 500000, 250000, 125000 microseconds

    time = oneSecInUsec / i; // time is used to toggle the LED is divided by i

    CurieTimerOne.start(time, &timedBlinkIsr);  // set timer and callback

#ifdef SERIAL_PORT_LOG_ENABLE

    Serial.print("The blink period: ");

    Serial.println(time);
#endif

    delay(10000);  // 10 seconds of delay, regularly 'interrupted' by the timer interrupt

#ifdef SERIAL_PORT_LOG_ENABLE

    Serial.print("Total number of ticks in 10 seconds: ");

    Serial.println(CurieTimerOne.rdRstTickCount());  // Reads and Resets tick count

    Serial.println("----");
#endif

    // Uncomment the following line if the serial logging is disabled

    // CurieTimerOne.restart(time);   // Restarts Timer

  }
}

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