Repeater

A scheduling library for Arduino, which is extremely simple and lightweight.

The basic idea

• You define an array of functions.
• You create a Repeater that calls these functions repeatedly.
• Every function has to return the milliseconds to wait until it wants be called again.

Features

• Extremely simple and lightweight
• The Repeater dynamically calculates, how long you may delay() your main loop between function calls to maximize your energy efficency. The Repeater will never call delay() by itself.

Limits

• You can't dynamically add/remeove functions to/from a Repeater once it is created.
• A function call can be delayed by other scheduled functions that take to long. (Non preemptive strategy, Execution deviation)
• You must not make any assumptions in your code about the execution order of scheduled functions.

Example

This is a fully working Arduino example sketch. It will be followed by a step-by-step explaination.

#include <Repeater.h>


unsigned long everySecond(){
  Serial.println("1 Second has passed!");
  return 1000;
}

unsigned long everyTwoSeconds(){
  Serial.println("2 Seconds have passed!");
  return 2000;
}


TaskFunction tasks[] = {everySecond, everyTwoSeconds};

Repeater repeater(tasks, 2);

void setup() {
  Serial.begin(9600);
}

void loop() {
  delay(repeater.tick());       
}

Step-by-Step

First, you need to include the library.

#include <Repeater.h>

---

Now you need a few functions, that can be scheduled. These functions have to return an unsigned long and take no arguments. Functions that match these criteria are defined as TaskFunction. The return value tells the Repeater how long it should wait until the TaskFunction want's to be called again (in milliseconds).

unsigned long everySecond(){
  Serial.println("1 Second has passed!");
  return 1000;
}

unsigned long everyTwoSeconds(){
  Serial.println("2 Seconds have passed!");
  return 2000;
}

---

The next step is to create an array of TaskFunctions that can be passed to the Repeater.

TaskFunction tasks[] = { everySecond, everyTwoSeconds};

---

Now it's time to create a Repater. It's constructor takes two arguments. The first agrument is a TaskFunction array. The second argument is the number of elements in that array.

Repeater repeater(tasks,2);

If you don't like the hardcoded 2, you can get the number of array elements by doing the following calculation. This, however, works only if the array was not passed as a function argument to your code.

sizeof(tasks)/sizeof(tasks[0])

---

The last step is to call the Repeaters tick() method in your main loop. Every time the tick() method is called, the Repeater will call all scheduled TaskFunctions that are due.

The tick() method returns an unsigned long that describes aproximately the time in milliseconds until the next tick() call needs to be done. You may delay your main loop by exactly this amount of time to maximize your energy efficency.

void loop() {
  delay(repeater.tick());       
}

Disclaimer

• Since I'm a Java Developer, writing C++ code is for me quite unintuitive. Please tell me if I did something stupid or unconventional.
• There are some much more advanced scheduling libraries for Arduino available. This library is not going to compete with them.
• I want to keep it as simple and stupid as possible.