Task Library

By default, Energia considers each sketch on .ino file as a task and create them as an endless loop in the RTOS scheduler.

However, creating other tasks may be interesting, especially for a better control.

I explain how Energia works and discuss three solutions, two of them actually work.

What Energia Does

Energia considers each sketch as a task with two functions: initial setup() and to-be-repeated loop(). 

Energia performs some under-the-hood work: it runs the function 
setup() once and includes the loop() function inside an endless loop. 

xdc_Void the_task(xdc_UArg _task_setup, xdc_UArg _task_loop)

{

    /* Call setup once */

    (*(void(*)()) _task_setup)();

    

    /* Call loop repeatedly */

    for(;;) {

        (*(void(*)()) _task_loop)();

        System_flush();

        Task_yield();

    }

}

Let's Try

The rtosGlobals.h header includes the standard libraries and defines the  task myTask and the timer myTimer, required by the third solution only.  

The mains ketch can be kept with empty setup() and loop() functions.

///

/// @author Rei Vilo

/// @date Jun 23, 2015 10:32

/// @version 101

///

/// @copyright (c) Rei Vilo, 2015

/// @copyright CC = BY SA NC

///

// Core library

#include "Energia.h"

// Include application, user and local libraries

#include "Task.h"

#include "Timer.h"

// Define variables and constants

Task myTask;

Timer myTimer;

uint8_t valueB = 0;

First Solution

The first solution is very similar to the standard implementation of the tasks as sketches by Energia, where the function is included in an endless loop.  

Note that the initialisation of the port is done in the rtosSetup() function.

myTask.begin() defines the function to be called, sets the priority and runs the function once. The priority is a value between 0 and Task_numPriorities -1. Task_numPriorities is a constant provided by RTOS, which value is 16 or 32 and depends on the system.

void functionTask()

{

    // Solution 1: with loop, works fine

    while (true)

    {

        valueB = 1 - valueB;

        digitalWrite(BLUE_LED, valueB);

        delay(333);

    }

}

// Add optional rtosSetup function

void rtosSetup()

{

    pinMode(BLUE_LED, OUTPUT);

    myTask.begin(functionTask, Task_numPriorities - 1);

}

Second Solution Doesn't Work

The second solution doesn't work, as the function functionTask() doesn't include any endless loop. 

Because the task is scheduled only once by myTask.begin(), it runs only once.

void functionTask()

{

    // Solution 2: with delay, doesn't work

    valueB = 1 - valueB;

    digitalWrite(BLUE_LED, valueB);

    delay(333);

}

// Add optional rtosSetup function

void rtosSetup()

{

    pinMode(BLUE_LED, OUTPUT);

    myTask.begin(functionTask, Task_numPriorities - 1);

}

Third and Best Solution

The third and last solution is the cleanest one.

The function functionTask() only toggles the value LED and is called by the timer myTimer every 333 ms.

void functionTask()

{

    // Solution 3: with Timer, works fine

    valueB = 1 - valueB;

    digitalWrite(BLUE_LED, valueB);

}

// Add optional rtosSetup function

void rtosSetup()

{

    pinMode(BLUE_LED, OUTPUT);

    myTask.begin(functionTask, Task_numPriorities - 1);

    // Solution 3: with Timer, works fine

    myTimer.begin(functionTask, 333);

    myTimer.start();

}

My recommendation is to go for the third solution, where the function of the task functionTask() is explicitly called by a timer or a clock.