This document discusses using an RTOS (real-time operating system) called DuinOS, which is a version of FreeRTOS for Arduino boards, to enable multitasking capabilities. It provides an example of DuinOS running multiple tasks concurrently for blinking different colored LEDs. While DuinOS allows basic multitasking, its documentation is limited and communication between tasks needs improvement. Alternatives like NILRTOS were also explored but have their own limitations for more complex applications. In conclusion, DuinOS shows promise as an RTOS for Arduino but still requires further development and documentation to reach its full potential.

1. Open source Real-Time
Operating System with Arduino.

2. Agenda
• Introduction
• Concept of RTOS
• FreeRTOS
• DuinOS – FreeRTOS for Arduino
• Example of multitask running with DuinOS
• Communication
• What needs to be improved
• Limitations of Arduino
• Other approach tried
• Other things learned
• Further Development
• Conclusion
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3. Introduction
• Interest in the PMC project.
• Problem: Command sent to the board takes some
time to execute, as it runs in an loop.
• Need for a client/server running simultaneously.
• Solution sugested – RTOS.
• RTOS could provide a better use of Arduino’s
resources.
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4. Concept of RTOS
• RTOS – Real-Time Operating System.
• Real-time: Rigid control of time processing
considering the inputs.
• Dividing duties requires capability to:
 Switch task without corruption.
 Determine priorities when conflicts occur.
 Provide clean, independent storage for each task.
 Provide inter-task communication when required.
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5. How does an RTOS work?
• Two most common designs:
 Event-driven switch task; when a higher priority
need servicing, called preemptive priority or priority
scheduling.
 Time-sharing desings switch tasks on a regular
clocked interrupt, called Round Robin.
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6. Characteristics of FreeRTOS
• Lightweight embeddable multi-task real-time
operating system.
• Cooperative, preemptive and hybrid scheduling.
• Use of tasks and co-routines.
• Multiple inter-tasks communication (queues,
semaphores, mutexes).
• The scheduling works with priorities.
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7. Block diagram of a FreeRTOS task
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8. DuinOS – FreeRTOS version for Arduino
• RTOS with a preemptive multitasking system for
Arduino and Atmel AVR based boards.
• Developed by RobotGroup, from Argentina.
• Open-source, with contribution of people from
USA, Brazil, Italy…
• Still in development, however very recent changes
were not found in the project.
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9. Particularities of duinOS
The language is turned into easier commands in order
to be more acessible to an Arduino user:
• Suspend task:
#define suspend() vTaskSuspend(NULL)
• Delay command turned into Task delay:
#define delay(ticks) vTaskDelay(ticks)
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10. Example of a duinOS multitask
application running
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• Task declaration:
declareTaskLoop(redLED); declareTaskLoop(greenLED);
declareTaskLoop(yellowLED); declareTaskLoop(read_button);
• Tasks:
taskLoop(redLED) :Blinks red LED 10 times every second and then suspend.
taskLoop(greenLED): Blinks green LED every second.
taskLoop(yellowLED): Blinks yellow LED twice a second.
taskLoop(read_button): If button is pressed, suspends green and yellow LED tasks, turn
off LEDs and resumes the rel LED task.
• Task start. Goes in setup function:
createTaskLoop(redLED, NORMAL_PRIORITY); createTaskLoop(greenLED,
LOW_PRIORITY); createTaskLoop(yellowLED, HIGH_PRIORITY)....
• Loop function is empty! All delay used in the tasks is processing time for another task.

11. Communication tasks using DuinOS
• In a first moment, the connection routine
was developed in the setup.
• Then, it was developed a connection task.
• Next Step: Server-specific task and a client-
specific task. Both wait until the connection
is established to start running, through inter-
task communication.
• Watchdog was used in the prototype.
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12. • Client declaration not working in a first moment.
Issued solved waiting for the connection, using
inter-task communication to start the task.
• Reception of the HTTP request was not occuring
correctly. Solved adding more delay between each
step, resulting in more free time for the other tasks
to run.
• A blink LED task run at the same time in order to
show Arduino was still running.
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Communication tasks using DuinOS

13. What needs to be improved
• Creation of a socket inside the Task. Arduino to
browser communication is established but no data
os received. Probably because of the lack of socket
information inside the task.
• Task exclusively to write in the database.
• Lack of documentation of DuinOS!
• Explore more the use of semaphores and mutexes
instead of global variables.
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14. Limitations of Arduino and duinOS
• Need for step by step execution of the code.
• Socket creation inside a task??
• Lack of documentation of DuinOS affects the results
of using this RTOS in a project!
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15. Other approach tried - NILRTOS
• NilRTOS is fast tiny preemptive RTOS.
• Designed specially for Arduino UNO.
• Working perfectly for the client. All data is received
by the browser.
• Work simply by adding a Library to normal Arduino.
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16. NILRTOS
• Highlights:
• // Declare a stack with 128 bytes beyond context switch and interrupt needs.
NIL_WORKING_AREA(waThread1, 128);
• NIL_THREAD(Thread1, arg) {
• Threads declaration:
NIL_THREADS_TABLE_BEGIN()
NIL_THREADS_TABLE_ENTRY(NULL, Thread1, NULL, waThread1, sizeof(waThread1))
NIL_THREADS_TABLE_END()
• Semaphore declaration, with an initial value of 0:
SEMAPHORE_DECL(sem, 0);
• // Sleep so lower priority threads can execute.
nilThdSleep(100);
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17. Limitations of NILRTOS
• One task has to be stopped, so the others can run.
• In a RTOS, the “jump” between different tasks have to
be executed by the system and not defined by the
user.
• Suggested not to use NiLRTOS, as it is not a proper
functioning RTOS.
• Not suitable for my project. However, several
concepts of RTOS were learned while trying this
approach.
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18. Other things learned
• Basics of PHP and MySQL.
• Database configuration and access control using
Wamp server.
• HTTP protocol request and response.
• Object oriented programming; classes and objects.
• Watchdogs.
• Semaphores and mutexes.
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19. Other possibilities
• Use of idle tasks with a hook to initiate the task,
allowing the use of Arduino in a low energy mode.
• Get better documentation and examples.
• In order to better understand how the RTOS
improve the use of a microcontroler, a more
powerful IDE than Arduino needs to be used.
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20. Conclusion
• RTOS is a very powerful solution for embedded
systems, which can improve the funcionality of na
embedded system.
• However one microcontroller can run only one task
at a time, with a powerful scheduler and a well
planed application it appear that several tasks are
being executed at the same time.
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21. Conclusion
• DuinOS is a good RTOS for Arduino, however some
points need to be improved and a proper
documentation still has to be created.
• The communication libraries of DuinOS need to be
improved in order to get a better functionality.
• NILRTOS is a working RTOS which can be perfectly
used for small applications, specially with UNO, in
order to achieve a certain level of multitasking.
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22. Thank you.