arkhipenko
/
TaskScheduler
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<p class=MsoNormal><b>Task Scheduler – cooperative multitasking for Arduino microcontrollers</b></p>

<p class=MsoNormal><b>Version 1.51: 2015-09-20</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>REQUIREMENT</b>:</p>

<p class=MsoNormal>A lightweight implementation of the task scheduling
supporting:</p>

<ol style='margin-top:0in' start=1 type=1>
 <li class=MsoNormal>execution period (n times per second)</li>
 <li class=MsoNormal>number of iterations (n times)</li>
 <li class=MsoNormal>execution of tasks in predefined sequence</li>
 <li class=MsoNormal>dynamic change of the execution parameters for both tasks
     and execution schedule</li>
 <li class=MsoNormal>power saving via entering IDLE sleep mode if no tasks are
     scheduled to run</li>
</ol>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>IDEA</b>:</p>

<p class=MsoNormal>“Task” is a container concept that links together:</p>

<ol style='margin-top:0in' start=1 type=1>
 <li class=MsoNormal>Execution interval</li>
 <li class=MsoNormal>Number of execution iterations</li>
 <li class=MsoNormal>A piece of code performing the task activities (callback
     function)</li>
</ol>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>Tasks are linked into execution chains, which are processed
by the “Scheduler” in the order they are linked.</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>Tasks are responsible for supporting cooperative
multitasking by being “good neighbors”, i.e., running their callback functions
in a non-blocking way and releasing control as soon as possible. </p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>“Scheduler” is executing Tasks' callback functions in the
order the tasks were added to the chain, from first to last. Scheduler stops
and exists after processing the chain once in order to allow other statements
in the main code of <b>loop()</b> function to run.&nbsp; This a “scheduling
pass”.</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>If compiled with <span style='font-family:"Courier New"'>_TASK_SLEEP_ON_IDLE_RUN</span>
enabled, the scheduler will place processor into IDLE sleep mode (for
approximately 1 ms, as the timer interrupt will wake it up), after what is
determined to be an “idle” pass. An Idle Pass is a pass through the chain when
no Tasks were scheduled to run their callback functions. This is done to avoid
repetitive empty passes through the chain when no tasks need to be executed. If
any of the tasks in the chain always requires immediate execution (aInterval =
0), then there will be no end-of-pass delay.</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>Note: </b>Task Scheduler uses <b>millis()</b> to
determine if tasks are ready to be invoked. Therefore, if you put your device
to any “deep” sleep mode disabling timer interrupts, the <b>millis()</b> count
will be suspended, leading to effective suspension of scheduling. Upon wake up,
active tasks need to be re-enabled, which will effectively reset their internal
time scheduling variables to the new value of <b>millis(). </b>Time spent in
deep sleep mode should be considered “frozen”, i.e., if a task was scheduled to
run in 1 second from now, and device was put to sleep for 5 minutes, upon wake
up, the task will still be scheduled 1 second from the time of wake up.
Executing <b>enable() </b>function on this tasks will make it run as soon as
possible. This is a concern only for tasks which are required to run in a truly
periodical manner (in absolute time terms). </p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>COMPILE PARAMETERS:</b></p>

<p class=MsoNormal>This library could be compiled with several options. </p>

<p class=MsoNormal>These parameters must be defined before inclusion of the
library header file into the sketch.</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>#define <b>_TASK_TIMECRITICAL</b></p>

<p class=MsoNormal>...will compile the library with time critical tracking
option enabled.</p>

<p class=MsoNormal>Time critical option keeps track where next execution time
of the task falls, and makes it available via API through Task::<b> getOverrun()
</b>function. If <b>getOverrun </b>returns a negative value, this Task’s next
execution time is in the past, and task is behind schedule. This most probably
means that either task’s callback function runtime is too long, or the
execution interval is too short (then schedule is too aggressive).</p>

<p class=MsoNormal>A positive value indicates that task is on schedule, and
callback functions have enough time to finish before the next scheduled pass. </p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>#define <b>_TASK_SLEEP_ON_IDLE_RUN</b></p>

<p class=MsoNormal>...will compile the library with the <b>sleep</b> option
enabled (AVR boards only).</p>

<p class=MsoNormal>When enabled, scheduler will put the microcontroller into <b>SLEEP_MODE_IDLE</b>
state if none of the tasks’ callback functions were activated during pass. <b>IDLE</b>
state is interrupted by timers once every 1 ms. Helps conserve power. &nbsp;Device
in SLEEP_MODE_IDLE wakes up to all hardware and timer interrupts, so scheduling
is kept current.</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>NOTE: above parameters are DISABLED by default, and need
to be explicitly enabled.</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>API DOCUMENTATION:</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>TASKS:</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>CREATION:</p>

<p class=MsoNormal><b>Task();</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Default constructor. </p>

<p class=MsoNormal style='margin-left:35.45pt'>Takes no parameters and creates
a task that could be scheduled to run at every scheduling pass indefinitely,
but does not have a callback function defined, so no execution will actually
take place. </p>

<p class=MsoNormal style='margin-left:35.45pt'>All tasks are created <b>disabled</b>
by default.</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='page-break-after:avoid'><b>Task(unsigned long aInterval,
long aIterations, void (*aCallback)(), Scheduler* aScheduler, bool aEnable);</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Constructor with parameters. </p>

<p class=MsoNormal style='margin-left:35.45pt'>Creates a task that is scheduled
to run every &lt;aInterval&gt; milliseconds, &lt;aIterations&gt; times,
executing &lt;aCallback&gt; function on every pass. </p>

<p class=MsoNormal style='margin-left:71.45pt;text-indent:-.25in'>1.<span
style='font-size:7.0pt;font-family:"Times New Roman","serif"'>&nbsp;&nbsp;&nbsp;
</span>aInterval is in milliseconds</p>

<p class=MsoNormal style='margin-left:71.45pt;text-indent:-.25in'>2.<span
style='font-size:7.0pt;font-family:"Times New Roman","serif"'>&nbsp;&nbsp;&nbsp;
</span>aIteration in number of times, -1 for indefinite execution<br>
<b>Note: </b>Tasks do not remember the number of iteration set initially. After
the iterations are done, internal iteration counter is 0. If you need to
perform another set of iterations, you need to set the number of iterations
again. <br>
<b>Note: </b>Tasks which performed all their iterations remain active. </p>

<p class=MsoNormal style='margin-left:71.45pt;text-indent:-.25in'>3.<span
style='font-size:7.0pt;font-family:"Times New Roman","serif"'>&nbsp;&nbsp;&nbsp;
</span>aCallback is a pointer to a void function without parameters</p>

<p class=MsoNormal style='margin-left:71.45pt;text-indent:-.25in'>4.<span
style='font-size:7.0pt;font-family:"Times New Roman","serif"'>&nbsp;&nbsp;&nbsp;
</span>aScheduler – <b>optional</b> reference to existing scheduler. If
supplied (not NULL) this task will be appended to the task chain of the current
scheduler). <b>Default=NULL</b></p>

<p class=MsoNormal style='margin-left:71.45pt;text-indent:-.25in'>5.<span
style='font-size:7.0pt;font-family:"Times New Roman","serif"'>&nbsp;&nbsp;&nbsp;
</span>aEnable – <b>optional</b>. Value of <b>true </b>will create task
enabled. <b>Default = false</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>All tasks are created <b>disabled</b>
by default (unless aEnable = true). You have to explicitly enable the task for
execution.</p>

<p class=MsoNormal style='margin-left:35.45pt'>Enabled task is scheduled for execution
immediately. Enable tasks with delay (standard execution interval or specific
execution interval) in order to defer first run of the task.</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>INFORMATION</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>The following 3 “getter”
functions return task status (enabled/disabled), execution interval in
milliseconds, number of <b><i>remaining</i></b> iterations. </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'><b>bool isEnabled() </b></p>

<p class=MsoNormal style='margin-left:35.45pt'><b>unsigned long getInterval()</b></p>

<p class=MsoNormal style='margin-left:35.45pt'><b>long getIterations() </b></p>

<p class=MsoNormal style='margin-left:35.45pt'><b>&nbsp;</b></p>

<p class=MsoNormal><b>long getOverrun()</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>If library is compiled with <span
style='font-family:"Courier New"'>_TASK_TIMECRITICAL</span> enabled, tasks are
monitored for “long running” scenario. A “long running” task is a task that
does not finish processing its callback functions quickly, and thus creates a
situation for itself and other tasks where they don't run on a scheduled
interval, but rather “catch up” and are behind.&nbsp; When task scheduler sets
the next execution target time, it adds Task's execution interval to the
previously scheduled execution time:</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
<b>next execution time = previous execution time + task execution interval</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>If <b>next execution time</b> happens
to be already in the past (<b>next execution time</b> &lt; <b>millis()</b>), then
task is considered <b><i>overrun</i></b>. <b>GetOverrun</b> function returns
number of milliseconds between next execution time and current time. If the <b>value
is negative</b>, the task is overrun by that many milliseconds. </p>

<p class=MsoNormal style='margin-left:35.45pt'>Positive value indicate number
of milliseconds of slack this task has for execution purposes. </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>bool isFirstIteration()</b></p>

<p class=MsoNormal><b>bool isLastIteration()</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>For tasks with a defined number
of iterations, indicates whether current pass is a first or a last iteration of
the task (respectively). </p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='page-break-after:avoid'><b>CONTROL:</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>void enable();</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Enables the task, and schedules
it for immediate execution (without delay) at this or next scheduling pass
depending on when the task was enabled. Scheduler will execute the next pass
without any delay because there is a task which was enabled and requires
execution. </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>void delay();</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Schedules the task for execution
after a delay (aInterval), but does not change the enabled/disabled status of
the task. </p>

<p class=MsoNormal style='margin-left:35.45pt'><b>&nbsp;</b></p>

<p class=MsoNormal><b>void enableDelayed();</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Enables the task, and schedules
it for execution after a delay (aInterval). </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>void enableDelayed (unsigned long aDelay);</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Enables the task, and schedules
it for execution after a specific delay (aDelay, which maybe different from aInterval).
</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>void restart();</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>For tasks with limited number of
iterations only, <b>restart</b> function will re-enable the task, set the
number of iterations back to when the task was created and and schedule the
task for execution as soon as possible.</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>void restartDelayed (unsigned long aDelay);</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Same as <b>restart() </b>function,
with the only difference being that Task is scheduled to run first iteration
after a delay = <b>aDelay</b> milliseconds.</p>

<p class=MsoNormal><b>&nbsp;</b></p>

<p class=MsoNormal><b>void disable();</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Disables the task. Scheduler
will not execute this task any longer, even if it remains in the chain.&nbsp; Task
can be later re-enabled for execution. </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>void disableOnLastIteration (bool aBool);</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Controls iterative task behavior
on the last iteration. If <b>aBool</b> is <b>true</b> task will be disabled
after last iteration. If <b>aBool</b> is <b>false</b>, task will remain active
(but not invoked until new number of iterations is set)</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>void set(unsigned long aInterval, long aIterations, void (*aCallback)());</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Allows dynamic control of all
task execution parameters in one function call. If task being modified is
active, it will be scheduled for execution immediately. </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal>Next three “setter” functions allow changes of individual
task execution control parameters. </p>

<p class=MsoNormal style='margin-left:35.45pt'><b>void setInterval (unsigned
long aInterval) </b></p>

<p class=MsoNormal style='margin-left:35.45pt'><b>void setIterations (long aIterations)
</b></p>

<p class=MsoNormal style='margin-left:35.45pt'><b>void setCallback (void
(*aCallback)()) </b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>Note: </b>Next execution time calculation takes place <b>after</b>
the callback function is called, so new interval will be used immediately by
the scheduler. For the situations when one task is changing the interval
parameter for the other, <b>setInterval</b> function calls <b>delay </b>explicitly
to guarantee schedule change, however it <b>does not </b>enable the task if
task is disabled. If task being modified is active, <b>setIterations </b>will
make the task be scheduled for execution immediately.</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>&nbsp;</b></p>

<p class=MsoNormal><b>TASK SCHEDULER:</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><b>CREATION:</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-bottom:12.0pt'><b>Scheduler()</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>Default constructor. </p>

<p class=MsoNormal style='margin-left:35.45pt'>Takes no parameters. Creates
task scheduler with default parameters and an empty task queue. </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>void init()</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Initializes the task queue and
scheduler parameters, Executed as part of constructor, so don't need to be
explicitly called after creation.</p>

<p class=MsoNormal style='margin-left:35.45pt'><b>Note: </b>be default (if
compiled with <span style='font-family:"Courier New"'>_TASK_TIMECRITICAL</span>
enabled) scheduler is allowed to put processor to IDLE sleep mode. If this
behavior was changed via <b>allowSleep() </b>function, <b>inti() </b>will <b>NOT</b>
reset allow sleep particular parameter. </p>

<p class=MsoNormal><br>
<b>void addTask(Task&amp; aTask)</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Adds task aTask to the execution
queue (or chain) of tasks by appending it to the end of the chain. If two tasks
are scheduled for execution, the sequence will match the order tasks are
appended to the chain. However, in reality, due to different timing of task
execution, the actual order will be different. </p>

<p class=MsoNormal style='margin-left:35.45pt'><b>Note: </b>Currently, changing
the execution dynamically is not supported. </p>

<p class=MsoNormal style='margin-left:35.45pt'>If you need to reorder the queue
– initialize the scheduler and re-add the tasks in a different order. </p>

<p class=MsoNormal><br>
<b>void deleteTask(Task&amp; aTask)</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Deletes task aTask from the
execution chain. The chain of remaining tasks is linked together (i.e</p>

<p class=MsoNormal style='margin-left:35.45pt'>if original task chain is 1 &#8594;
2 &#8594; 3 &#8594; 4, deleting 3 will result in 1 &#8594; 2 &#8594; 4).</p>

<p class=MsoNormal style='margin-left:35.45pt'><b>Note: </b>it is not required
to delete a task from the chain. A disabled task will not be executed anyway,
but you save a few microseconds per scheduling pass by deleting it, since it is
not even considered for execution. </p>

<p class=MsoNormal style='margin-left:35.45pt'>An example of proper use of this
function would be running some sort of <b>initialize</b> task in the chain, and
then deleting it from the chain since it only needs to run once. </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal><b>void allowSleep(bool aState) </b></p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Available in API only&nbsp; if compiled
with <span style='font-family:"Courier New"'>_TASK_TIMECRITICAL</span> enabled.
Controls whether scheduler is allowed (<b>aState =true</b>), or not (<b>aState =false</b>)
to put processor into IDLE sleep mode in case not tasks are scheduled to run.</p>

<p class=MsoNormal style='margin-left:35.45pt'>The <b>default</b> behavior of
scheduler upon creation is to allow sleep mode. </p>

<p class=MsoNormal><br>
<b>void enableAll()</b></p>

<p class=MsoNormal><b>void disableAll()</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>enables and disables
(respectively) all tasks in the chain. Convenient if your need to
enable/disable majority of the tasks (i.e. disable all and then enable one). </p>

<p class=MsoNormal style='margin-bottom:12.0pt'><br>
<b>Task&amp; currentTask()</b></p>

<p class=MsoNormal style='margin-left:35.45pt'>Returns reference to the task,
currently executing via <b>execute()</b> loop. Could be used by callback
functions to identify which of the </p>

<p class=MsoNormal><br>
<b>void execute()</b></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>Executes one scheduling pass,
including end-of-pass sleep. This function typically placed inside the <b>loop()</b>
function of the sketch. Since <b>execute</b> exits after every pass, you can
put additional statements after <b>execute</b> inside the <b>loop()</b> </p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'>&nbsp;</p>

<p class=MsoNormal style='page-break-after:avoid'><b>IMPLEMENTATION SCENARIOS
AND IDEAS:</b></p>

<p class=MsoNormal>&nbsp;</p>

<ol style='margin-top:0in' start=1 type=1>
 <li class=MsoNormal><b>EVENT DRIVEN PROGRAMMING</b></li>
</ol>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>Each of the processes of your application becomes a separate
and distinct programming area, which may or may not interact and control each
other. </p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal>Example: </p>

<p class=MsoNormal>In a plant watering system you need to measure soil
humidity, control pump and display the results</p>

<p class=MsoNormal>Each of the areas becomes a task:</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>Task
<b>tMeasure</b> (TMEASURE_INTERVAL*SECOND, -1, &amp;measureCallback);<br>
Task <b>tWater</b>&nbsp;&nbsp; (TWATER_INTERVAL*SECOND, RETRIES,
&amp;waterCallback);<br>
Task <b>tDisplay</b> (TDISPLAY_INTERVAL*SECOND, -1, &amp;displayCallback); </span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>Scheduler
<b>taskManager</b>;</span></p>

<p class=MsoNormal>Further, once you turn on the pump, you keep it running for
TWATER_INTERVAL interval and then turn it off. Turning off a pump is also a
task which only needs to run once for every time the pump is turned on:</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>Task
<b>tWaterOff</b> (WATERTIME*SECOND, 1,</span><span style='font-family:"Courier New"'>
&amp;waterOffCallback);</span></p>

<p class=MsoNormal>Example of the callback function:</p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>void waterOffCallback() {<br>
&nbsp;&nbsp;&nbsp; motorOff();<br>
&nbsp;&nbsp;&nbsp; tWater.enableDelayed();<br>
}</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>or</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>void waterCallback() {<br>
&nbsp;&nbsp;&nbsp; if (tWater.getIterations()) {</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>// If this is not the last iteration = turn the pump
on<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; motorOn();<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tWaterOff.set(parameters.watertime * SECOND, 1,
&amp;waterOffCallback);<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tWaterOff.enableDelayed();<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return;<br>
&nbsp;&nbsp;&nbsp; }</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>// We could not reach target humidity – something is
wrong<br>
&nbsp;&nbsp;&nbsp; motorOff;<br>
&nbsp;&nbsp;&nbsp; taskManager.disableAll();<br>
&nbsp;&nbsp;&nbsp; tError.enable();<br>
}</span></p>

<p class=MsoNormal><span style='font-family:"Courier New"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Your
sample <b>setup</b>() and <b>loop</b>() (partially) are as follows. </span></p>

<p class=MsoNormal><b><span style='font-family:"Times New Roman","serif"'>Note:
</span></b><span style='font-family:"Times New Roman","serif"'>please note that
tWater is <b>not</b> activated during setup(). It is activated by tMeasure
callback once the watering conditions are met. </span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
</span><span style='font-family:"Courier New"'>setup()</span></p>

<p class=MsoNormal><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
&nbsp; ...</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;
tWater.setIterations(parameters.retries);<br>
&nbsp; tWaterOff.setInterval(parameters.watertime * SECOND);<br>
<br>
<br>
&nbsp; taskManager.init();<br>
&nbsp; taskManager.addTask(tMeasure);<br>
&nbsp; taskManager.addTask(tDisplay);<br>
&nbsp; taskManager.addTask(tWater);<br>
&nbsp; taskManager.addTask(tWaterOff);<br>
&nbsp; <br>
&nbsp; tMeasure.enable();<br>
&nbsp; tDisplay.enable();<br>
<br>
&nbsp; currentHumidity = measureHumidity();<br>
}<br>
<br>
<br>
void loop ()<br>
{<br>
&nbsp; taskManager.execute();<br>
}</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'>&nbsp;</p>

<ol style='margin-top:0in' start=2 type=1>
 <li class=MsoNormal><b><span style='font-family:"Times New Roman","serif"'>“NATIVE”
     SUPPORT FOR FINITE STATE MACHINE</span></b></li>
</ol>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Define
“states” as callback function or functions. Each callback function executes
activities specific to a “state” and then “transitions” to the next state by
assigning next callback function to the task. </span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Transition
from one state to the next is achieved by setting next callback function at the
end of preceding one. </span></p>

<p class=MsoNormal><b><span style='font-family:"Times New Roman","serif"'>Note:
</span></b><span style='font-family:"Times New Roman","serif"'>do not call the
next callback function. Let the schedule take care of that during the next
pass. (Thus letting other tasks run). </span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Example:
Blinking LED 2 times a second could be achieved this way</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>Task
tLedBlinker (500, -1, &amp;ledOnCallback);</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>Scheduler
taskManager;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>void&nbsp;
ledOnCallback() {</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
turnLedOn();</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
tLedBlinker.setCallback(&amp;ledOffCallback);</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>}</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>void&nbsp;
ledOffCallback() {</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
turnLedOff();</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
tLedBlinker.setCallback(&amp;ledOnCallback);</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>}</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>setup()
{</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
taskManager.init();<br>
&nbsp; &nbsp;&nbsp; taskManager.addTask(tLedBlinker);</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
tLedBlinker.enable();</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>}</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>loop
() {</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;
taskManager.execute();</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-family:"Courier New"'>}</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Obviously
the example is simple, but gives the idea of how the tasks could be used to go
through states.</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<ol style='margin-top:0in' start=3 type=1>
 <li class=MsoNormal><b><span style='font-family:"Times New Roman","serif"'>MULTIPLE
     POSSIBLE CALLBACKS FOR TASK</span></b></li>
</ol>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>There may
be a need to select an option for callback function based on certain criteria,
or randomly. </span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>You can
achieve that by defining an array of callback function pointers and selecting
one based on the criteria you need. </span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Example:
when a robot detects an obstacle, it may go left, right backwards, etc. Each of
the “directions” or “behaviors” are represented by a different callback
function. </span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Another
example of using multiple callbacks:</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>You may
need to “initialize” variables for a particular task.</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>In this
case, define a tasks with two callbacks:</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>Task <b>tWork</b> (T_INTERVAL, -1,
&amp;workCallbackInit);</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>…</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>void&nbsp; workCallbackInit() {</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // do your
initializationstuff here</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // finally assigne
the main callback function </span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
tWork.setCallback(&amp;workCallback);</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>}</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>void workCallback() {</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // main callback
function</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; …</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>}</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>The task
will initialize during first execution pass and switch to “regular” callback
execution starting with second pass. There is a delay between first and second
passes of the task (scheduling period, if defined). In order to execute the
second pass immediately after initialization first pass, change the above code
like this:</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>void&nbsp; workCallbackInit() {</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // do your
initializationstuff here</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; // finally assigne the
main callback function </span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
tWork.setCallback(&amp;workCallback);</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tWork.enable();</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>}</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>The task
will run initialization first, then immediately second pass, and then switch to
processing at regular intervals starting with a third pass. </span></p>

<p class=MsoNormal>&nbsp;</p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<ol style='margin-top:0in' start=4 type=1>
 <li class=MsoNormal><b><span style='font-family:"Times New Roman","serif"'>INTERRUP-DRIVEN
     EXECUTION SUPPORT </span></b></li>
</ol>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>In case
of interrupt-driven program flow, tasks could be scheduled to run once to
request asynchronous execution (request), and then re-enabled (restarted) again
with a different callback function to process the results. </span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal><b><span style='font-family:"Times New Roman","serif"'>Example</span></b><span
style='font-family:"Times New Roman","serif"'>: event driven distance
calculation for ultrasonic pulses. EchoPin #6 triggers pin change interrupts on
rising and falling edges to determine the length of ultrasonic pulse.</span></p>

<p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>&nbsp;</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>#include &lt;DirectIO.h&gt;<br>
#include &lt;TaskScheduler.h&gt;<br>
#include &lt;PinChangeInt.h&gt;<br>
<br>
<br>
#define&nbsp; TRIGGERPIN 5<br>
#define&nbsp; ECHOPIN&nbsp;&nbsp;&nbsp; 6<br>
<br>
Output&lt;TRIGGERPIN&gt;&nbsp; pTrigger;<br>
Input&lt;ECHOPIN&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; pEcho;<br>
<br>
Scheduler r;<br>
<br>
Task&nbsp; tMeasure(1000, -1, &amp;measureCallback);<br>
Task&nbsp; tDisplay(1000, -1, &amp;displayCallback);<br>
Task&nbsp; tPing(0, 1, &amp;pingCalcCallback);<br>
<br>
<br>
volatile bool pulseBusy = false;<br>
volatile bool pulseTimeout = false;<br>
volatile unsigned long pulseStart = 0;<br>
volatile unsigned long pulseStop = 0;<br>
volatile unsigned long pingDistance = 0;<br>
<br>
<br>
void pingTrigger(unsigned long aTimeout) {<br>
&nbsp; if (pulseBusy) return;&nbsp; // do not trigger if in the middle of a
pulse<br>
&nbsp; if (pEcho == HIGH) return; // do not trigger if ECHO pin is high<br>
&nbsp; <br>
&nbsp; pulseBusy = true;<br>
&nbsp; pulseTimeout = false;</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'><br>
&nbsp; pTrigger = LOW;<br>
&nbsp; delayMicroseconds(4);<br>
&nbsp; pTrigger = HIGH;<br>
<br>
&nbsp; tPing.setInterval (aTimeout);<br>
<br>
&nbsp; delayMicroseconds(10);<br>
&nbsp; pTrigger = LOW; </span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>&nbsp;
tPing.restartDelayed(); // timeout countdown starts now</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>// will start the pulse clock on the rising edge of
ECHO pin</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>&nbsp;
PCintPort::attachInterrupt(ECHOPIN, &amp;pingStartClock, RISING); <br>
}<br>
<br>
</span></p>

<p class=MsoNormal style='margin-left:35.45pt'><span style='font-size:10.0pt;
font-family:"Courier New"'>// Start clock on the <b>rising</b> edge of the
ultrasonic pulse<br>
void pingStartClock() {<br>
&nbsp; pulseStart = micros();<br>
&nbsp; PCintPort::detachInterrupt(ECHOPIN); // not sure this is necessary<br>
&nbsp; PCintPort::attachInterrupt(ECHOPIN, &amp;pingStopClock, FALLING); <br>
&nbsp; tPing.restartDelayed();<br>
}<br>
<br>
// Stop clock on the <b>falling</b> edge of the ultrasonic pulse<br>
void pingStopClock() {<br>
&nbsp; pulseStop = micros();<br>
&nbsp; PcintPort::detachInterrupt(ECHOPIN);</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>&nbsp;
pingDistance = pulseStop - pulseStart;<br>
&nbsp; pulseBusy = false;<br>
&nbsp; tPing.disable(); // disable timeout<br>
}</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>//
Stop clock because of the timeout – the wave did not return<br>
void pingCalcCallback() {<br>
&nbsp; if (pulseBusy) {<br>
&nbsp;&nbsp;&nbsp; pingStopClock();<br>
&nbsp; }<br>
&nbsp; pulseTimeout = true;<br>
}<br>
<br>
<br>
<br>
// Initial measure callback sets the trigger<br>
void measureCallback() {<br>
&nbsp; if (pulseBusy) {&nbsp; // already measuring, try again<br>
&nbsp;&nbsp;&nbsp; tMeasure.enable();<br>
&nbsp;&nbsp;&nbsp; return;<br>
&nbsp; }<br>
&nbsp; pingTrigger(30); // 30 milliseconds or max range of ~5.1 meters<br>
&nbsp; tMeasure.setCallback(&amp;measureCallbackWait);<br>
}</span></p>

<p class=MsoNormal style='margin-top:0in;margin-right:0in;margin-bottom:12.0pt;
margin-left:35.45pt'><span style='font-size:10.0pt;font-family:"Courier New"'>//
Wait for the measurement to <br>
void measureCallbackWait() {<br>
&nbsp; if (pulseBusy) return;<br>
&nbsp; tMeasure.setCallback(&amp;measureCallback);&nbsp; <br>
}<br>
<br>
<br>
bool state = true;<br>
<br>
void displayCallback() {<br>
&nbsp; char d[256];<br>
&nbsp;&nbsp; <br>
&nbsp; unsigned long cm = pingDistance * 17 / 100; // cm<br>
&nbsp; <br>
&nbsp; snprintf(d, 256, &quot;pulseStart = %8lu\tpulseStop=%8lu\tdistance,
cm=%8lu&quot;, pulseStart, pulseStop, cm);<br>
&nbsp; Serial.println(d);<br>
&nbsp; <br>
}<br>
<br>
void setup() {<br>
&nbsp; // put your setup code here, to run once:<br>
&nbsp; <br>
&nbsp; Serial.begin(115200);<br>
&nbsp; <br>
<br>
&nbsp; pTrigger = LOW;<br>
&nbsp; pEcho = LOW;<br>
&nbsp; <br>
&nbsp; r.init();<br>
&nbsp; r.addTask(tDisplay);<br>
&nbsp; r.addTask(tMeasure);<br>
&nbsp; r.addTask(tPing);<br>
&nbsp; <br>
&nbsp; r.enableAll();<br>
&nbsp; tPing.disable();<br>
}<br>
<br>
void loop() {<br>
&nbsp; // put your main code here, to run repeatedly:<br>
&nbsp; r.execute();<br>
}</span></p>

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