Dear Arduino Fans,
I've made a small Real Time Operation System (RTOS) for Arduino, called
RTuinOS.
Meanwhile a number of test cases are running stable and I decided to
publish it now. Instead of lots of explanation I put chapter "Introduction"
of the manual here. Please find the complete installation (including the
complete manual) attached to this thread. The manual should be your
starting point of reading.
Thank you for your kind interest in RTuinOS; your feedback is welcome.
With kind regards
Peter Vranken
P.S. Meanwhile it turned out that the download of the setup file via this
post is not reliable. Occasionally, the operation aborts and reports an
invalid file. The reason is unclear. To circumvent the download problem, I
placed the setup file of RTuinOS at github, please see
https://github.com/PeterVranken/RTuinOS/blob/master/RTuinOS-0.9.1.zip. You
have to follow this link and and click on Button "Raw" to start the file
download.
Introduction
Arduino (
www.arduino.cc) is a popular open source and open hardware micro
controller platform for various purposes, mainly located in leisure time
projects. Arduino comes along with a simple to use integrated development
environment, which contains the complete tool chain to write source code,
to browse through samples and libraries, to compile and link the software
and to upload it to the board and flash it. The RTuinOS project adds the
programming paradigm of a real time operating system to the Arduino world.
Real time operating systems, or RTOS, strongly simplify the implementation
of technical applications which typically do things in a quite regular
way, like checking inputs and setting outputs accordingly every (fixed)
fraction of a second. For example, the temperature controller for a
heating installation could be designed this way. Temperature sensors,
which report the room temperatures are evaluated and the burner and maybe
some valves are controlled to yield the desired target temperature.
Furthermore, using a real time system the program could coincidentally and
regularly update a display to provide feedback - at the same or any other
rate. Regular, time based programming can be done without the need of CPU
consuming waiting loops as used in the implementation of Arduino's library
functions delay and delayMicroseconds. Real time operating systems
characterize the professional use of micro controllers.
RTuinOS is a small real time operating system (RTOS) for the Arduino
environment. It is simple to use and fits well into the existing Arduino
code environment. It adds the concept of pseudo-parallel execution threads
to the sketches.
The traditional Arduino sketch has two entry points; the function setup,
which is the place to put the initialization code required to run the
sketch and function loop, which is periodically called. The frequency of
looping is not deterministic but depends on the execution time of the code
inside the loop.
Using RTuinOS, the two mentioned functions continue to exist and continue
to have the same meaning. However, as part of the code initialization in
setup you may define a number of tasks having individual properties. The
most relevant property of a task is a C code function, which becomes the
so called task function. Once entering the traditional Arduino loop, all
of these task functions are executed in parallel to one another and to the
repeated execution of function loop. We say, loop becomes the idle task of
the RTOS.
A characteristic of RTuinOS is that the behavior of a task is not fully
predetermined at compile time. RTuinOS supports regular, time-controlled
tasks as well as purely event controlled ones. Tasks can be preemptive or
behave cooperatively. Task scheduling can be done using time slices and a
round robin pattern. Moreover, many of these modes can be mixed. A task is
not per se regular, its implementing code decides what happens and this
can be decided context or situation dependent. This flexibility is
achieved by the basic idea of having an event controlled scheduler, where
typical RTOS use cases are supported by providing according events, e.g.
absolute-point-in-time-reached. If the task's code decides to always wait
for the same absolute-point-in-time-reached event, then it becomes a
regular task. However, situation dependent the same task could decide to
wait for an application sent event - and give up its regular behavior. In
many RTOS implementations the basic characteristic of a task is determined
at compile time, in RTuinOS this is done partly at compile time and partly
at runtime.
RTuinOS is provided as a single source code file which is compiled
together with your other code, which now becomes an RTuinOS application.
In the most simple case, if you do not define any task, your application
will strongly resemble a traditional sketch: You implement your setup and
your loop function; the former will be run once at the beginning and the
latter repeatedly.
RTuinOS on its own can't be compiled, there need to be an application.
RTuinOS is organized as a package which combines the RTuinOS source file
with some sample applications which are the test cases at the same time.
The source code of each sample application is held in a separate folder,
named tc<nn>. Any of these can be selected for compilation. You may add
more folders, holding the source code of your RTuinOS applications. A
starting point of your application folder can be a copy of any of the
folders tc<nn>. The compilation always is the same. Run the makefile,
where the name of the folder (which doesn't need to be tc<nn>) is an
option on the command line. Refer to the manual for more.
The most relevant document to read is the manual of RTuinOS, found as
manual.pdf. The manual introduces the basic concept of RTuinOS and gives
an overview of its features and limitations:
Chapter 2 explains the basic principles of operation. Some core
considerations of the implementation are highlighted, but the relevant
documentation of the implementation is the code itself. It is commented
using doxygen (
www.doxygen.org) tags; the compiled doxygen documentation
is part of this project. It contains only the documentation of the global
objects of RTuinOS; to fully understand the implementation you will have
to inspect the source code itself, please refer to [1], [2], [3].
Chapter 3 lists and documents all elements of RTuinOS' API.
Chapter 4 explains how to write a well-working RTuinOS-application. The
chapter starts with a short recipe, which guarantees soon success. Here is
where you may start reading if you are already familiar with the concept
of an RTOS.
The manual closes with chapter 5, which gives an overview of possible
improvements and still missing and maybe later released features.
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