arduino-timer - library for delaying function calls

Simple non-blocking timer library for calling functions in / at / every specified units of time. Supports millis, micros, time rollover, and compile time configurable number of tasks.

Use It

Include the library and create a Timer instance.

#include <arduino-timer.h>

auto timer = timer_create_default();

Or using the Timer constructors for different task limits / time resolution

Timer<10> timer; // 10 concurrent tasks, using millis as resolution
Timer<10, micros> timer; // 10 concurrent tasks, using micros as resolution
Timer<10, micros, int> timer; // 10 concurrent tasks, using micros as resolution, with handler argument of type int

Call timer.tick() in the loop function

void loop() {
    timer.tick();
}

Make a function to call when the Timer expires

bool function_to_call(void *argument /* optional argument given to in/at/every */) {
    return true; // to repeat the action - false to stop
}

Call function_to_call in delay units of time (unit of time defaults to milliseconds).

timer.in(delay, function_to_call);
timer.in(delay, function_to_call, argument); // or with an optional argument for function_to_call

Call function_to_call at a specific time.

timer.at(time, function_to_call);
timer.at(time, function_to_call, argument); // with argument

Call function_to_call every interval units of time.

timer.every(interval, function_to_call);
timer.every(interval, function_to_call, argument); // with argument

To cancel a Task

auto task = timer.in(delay, function_to_call);
timer.cancel(task);

To cancel all Tasks

timer.cancel();

Check if a timer is empty - no active Tasks

if (timer.empty()) { /* no active tasks */ }

Get the number of active Tasks

auto active_tasks = timer.size();

Be fancy with lambdas

timer.in(1000, [](void*) -> bool { return false; });
timer.in(1000, [](void *argument) -> bool { return argument; }, argument);

Getting the number of ticks until the next Task

auto ticks = timer.ticks(); // usefull for sleeping until the next task

void loop {
    auto ticks = timer.tick(); // returns the number of ticks
}

Avoiding ticks calculation inside of tick

void loop {
    timer.tick<void>(); // avoids ticks() calculation
}

API

/* Constructors */
/* Create a timer object with default settings:
   millis resolution, TIMER_MAX_TASKS (=16) task slots, T = void *
*/
Timer<> timer_create_default(); // auto timer = timer_create_default();

/* Create a timer with max_tasks slots and time_func resolution */
Timer<size_t max_tasks = TIMER_MAX_TASKS, unsigned long (*time_func)(void) = millis, typename T = void *> timer;
Timer<> timer; // Equivalent to: auto timer = timer_create_default()
Timer<10> timer; // Timer with 10 task slots
Timer<10, micros> timer; // timer with 10 task slots and microsecond resolution
Timer<10, micros, int> timer; // timer with 10 task slots, microsecond resolution, and handler argument type int

/* Signature for handler functions - T = void * by default */
bool handler(T argument);

/* Timer Methods */
/* Ticks the timer forward, returns the ticks until next event, or 0 if none */
unsigned long tick(); // call this function in loop()

/* Calls handler with opaque as argument in delay units of time */
Timer<>::Task
in(unsigned long delay, handler_t handler, T opaque = T());

/* Calls handler with opaque as argument at time */
Timer<>::Task
at(unsigned long time, handler_t handler, T opaque = T());

/* Calls handler with opaque as argument every interval units of time */
Timer<>::Task
every(unsigned long interval, handler_t handler, T opaque = T());

/* Cancel a timer task */
void cancel(Timer<>::Task &task);
/* Cancel all tasks */
void cancel();

/* Returns the ticks until next event, or 0 if none */
unsigned long ticks();

/* Number of active tasks in the timer */
size_t size() const;

/* True if there are no active tasks */
bool empty() const;

Installation

Check out the instructions from Arduino.

OR copy src/arduino-timer.h into your project folder (you won't get managed updates this way).

Examples

Found in the examples/ folder.

The simplest example, blinking an LED every second (from examples/blink):

#include <arduino-timer.h>

auto timer = timer_create_default(); // create a timer with default settings

bool toggle_led(void *) {
  digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN)); // toggle the LED
  return true; // keep timer active? true
}

void setup() {
  pinMode(LED_BUILTIN, OUTPUT); // set LED pin to OUTPUT

  // call the toggle_led function every 1000 millis (1 second)
  timer.every(1000, toggle_led);
}

void loop() {
  timer.tick(); // tick the timer
}

LICENSE

Check the LICENSE file - 3-Clause BSD License

Notes

Currently only a software timer. Any blocking code delaying timer.tick() will prevent the timer from moving forward and calling any functions.

The library does not do any dynamic memory allocation.

The number of concurrent tasks is a compile time constant, meaning there is a limit to the number of concurrent tasks. The in / at / every functions return NULL if the Timer is full.

A Task value is valid only for the timer that created it, and only for the lifetime of that timer.

Change the number of concurrent tasks using the Timer constructors. Save memory by reducing the number, increase memory use by having more. The default is TIMER_MAX_TASKS which is currently 16.

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