Micro-Controller Operating Systems: Difference between revisions

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{{Short description|Real-time operating system}}

{{Cleanup|reason=this article does not read like a good encyclopedia article.|date=February 2016}}

{{Infobox OS

| name = MicroC/OS (μC/OS)

| logo =

| caption =

| developer = Micrium, Inc.,<br />Silicon Labs

| family =

| source model = [[Open Source]], Apache license (as of 2020)

| working state = Current

| released = {{Start date and age|1991}}

| source model = [[Open-source Sourcesoftware|Open-source]], Apache license (as of 2020)

| supported platforms = [[ARM Cortex-M#Cortex-M3|ARM Cortex-M3]], [[ARM Cortex-M#Cortex-M4|Cortex-M4F]], [[ARM7#ARM7TDMI|ARM7TDMI]]; [[Atmel AVR]]; [[eSi-RISC]], and many others.

| released = {{Start date and age|1991}}

| ui = μC/[[Graphical user interface|GUI]]

| family = [[Real-time operating system]]s

| latest release version = OS-III

| latest release date = {{Start date and age|2016}}

| repo = {{URL|https://github.com/weston-embedded/uC-OS3}}

| marketing target = [[Embedded device]]s

| programmed in marketing target = [[ANSIEmbedded Cdevice]]s

| kernel type programmed in = [[MicrokernelANSI C]]

| language = English

| supported platforms = [[ARM Cortex-M#Cortex-M3|ARM Cortex-M3]], [[ARM Cortex-M#Cortex-M4|Cortex-M4F]], [[ARM7#ARM7TDMI|ARM7TDMI]]; [[Atmel AVR]]; [[eSi-RISC]], and many others.

| working state = Current

| family kernel type = [[Real-time operating system|Real-time]] [[microkernel]]s

| license = [[Open Source]] as of 2020. Previously [[Commercial software|Commercial]], [[freeware]] education use.

| ui = μC/[[Graphical user interface|GUI]]

| website = {{URL|www.micrium.com/products}}

| license = [[OpenApache SourceLicense|Apache]] as of 2020.; Previouslyformer [[Commercial software|Commercial]], [[freeware]] education use.

| repo = {{URL|github.com/SiliconLabs}}

| website = {{URL|https://weston-embedded.com/micrium/overview}}

}}

{{Infobox OS

'''Micro-Controller Operating Systems''' ('''MicroC/OS''', stylized as '''μC/OS''') is a [[real-time operating system]] (RTOS) designed Jean J. Labrosse in 1991. It is a priority-based [[Preemption (computing)|preemptive]] [[Real-time computing|real-time]] kernel for [[microprocessor]]s, written mostly in the programming language [[C (programming language)|C]]. It is intended for use in [[embedded system]]s.

| name = Micrium OS

| logo =

| caption =

| developer = Silicon Labs

| family =

| working state = Current

| source model = [[Open-source software|Open-source]]

| released = {{Start date and age|2020}}

| latest release version = Part of Gecko Platform 4.2.0.0,<ref>{{cite web|url=https://www.silabs.com/documents/public/release-notes/gecko-platform-release-notes-4.2.0.0.pdf|title=Gecko Platform 4.2.0.0 GA|access-date=2023-01-04|date=2022-12-14}}</ref> part of Gecko SDK 4.2.0.0<ref>{{cite web|url=https://github.com/SiliconLabs/gecko_sdk/releases|title=gecko_sdk Releases on github.com|website=[[GitHub]] |access-date=2023-01-04}}</ref>

| latest release date = {{Start date and age|2022|12|14}}

| repo = {{URL|https://github.com/SiliconLabs/gecko_sdk/tree/gsdk_4.2/platform/micrium_os}}

| marketing target = [[Embedded device]]s

| programmed in = [[ANSI C]]

| language = English

| supported platforms = exclusively Silicon Labs silicon

| kernel type = [[Real-time operating system|Real-time]] [[microkernel]]

| license = [[Apache License|Apache]]

| website = {{URL|https://www.silabs.com/developers/micrium-os}}

}}

{{Infobox OS

| name = Cesium RTOS

| logo =

| caption =

| developer = Weston Embedded Solutions

| family =

| working state = Current

| source model = [[Commercial software|Commercial]]

| released = {{Start date and age|2020|06|23}} (forked from uC/OS-III V3.08.00)<ref name=cesium_changelog>{{cite web|url=https://weston-embedded.com/cesium-release-notes/cs-os3-release-notes|title=Cs/OS3 Release Notes|publisher= Weston Embedded Solutions}}</ref>

| latest release version = Cs/OS3 3.09.05<ref name=cesium_changelog />

| latest release date = {{Start date and age|2025|04|22}}<ref name=cesium_changelog />

| marketing target = [[Embedded device]]s

| programmed in = [[ANSI C]]

| language = English

| supported platforms = 50+ unclear whether there is a 1-to-1 overlap with μC/OS

| kernel type = [[Real-time operating system|Real-time]] [[microkernel]]

| license = [[Commercial software|Commercial]]

| website = {{URL|www.micriumweston-embedded.com/products/cesium}}

}}

'''Micro-Controller Operating Systems''' ('''MicroC/OS''', stylized as '''μC/OS''', or '''Micrium OS''') is a [[real-time operating system]] (RTOS) designed by Jean J. Labrosse in 1991. It is a priority-based [[Preemption (computing)|preemptive]] [[Real-time computing|real-time]] kernel for [[microprocessor]]s, written mostly in the programming language [[C (programming language)|C]]. It is intended for use in [[embedded system]]s.

MicroC/OS allows defining several functions in C, each of which can execute as an independent thread or task. Each task runs at a different priority, and runs as if it owns the [[central processing unit]] (CPU). Lower priority tasks can be preempted by higher priority tasks at any time. Higher priority tasks use operating system (OS) services (such as a delay or event) to allow lower priority tasks to execute. OS services are provided for managing tasks and memory, communicating between tasks, and timing.<ref>{{cite web |url=httphttps://people.ece.cornell.edu/land/courses/ece5760/NiosII_muCOS/ |title=NiosII GCC with MicroC/OS |author=<!--Not statedUnstated--> |date=June 2006 |website=School of Electrical and Computer Engineering |publisher=Cornell University |access-date=25 April 2017}}</ref>

==History==

The MicroC/OS kernel was published originally in a three-part article in Embedded Systems Programming magazine and the book ''μC/OS The Real-Time Kernel'' by Labrosse.<ref>{{cite book |last=Labrosse |first=Jean J. Labrosse|date=15 June 2002 ({{ISBN|0title=μC/OS The Real-87930Time Kernel |edition=2nd |publisher=CRC Press |isbn=978-444-81578201037}}). The</ref> authorHe intended at first to simply describe the internals of a [[Software portability|portable]] operating systemOS he had developed for his own use, but later developed the OSit as a commercial product in his own company Micrium, Inc. in versions II and III.

In 2016 Micrium, Inc. was acquired by Silicon Laboratories<ref>{{cite web|url=https://weston-embedded.com/about-micrium|title=What is Micrium?|access-date=2023-01-04|publisher=Weston Embedded Solutions}}</ref> and it was subsequently released as open-source under the [[Apache license]].

Silicon Labs continues to maintain an open-source product named Micrium OS for use on their own silicon<ref>{{cite web|url=https://www.silabs.com/developers/micrium|title=Micrium Software and Documentation|access-date=2023-01-04}}</ref> and a group of former Micrium, Inc. employees (including Labrosse) provides consultancy and support for both μC/OS and Cesium RTOS, a proprietary fork made just after the open-source release.<ref>{{cite web|url=https://weston-embedded.com/why-cesium|title=Why Cesium RTOS?|access-date=2023-01-04|publisher= Weston Embedded Solutions}}</ref>

==μC/OS-II==

Based on the source code written for μC/OS, and introduced as a commercial product in 1998, μC/OS-II is a [[Software portability|portable]], ROM-able, [[scalable]], preemptive, real-time, deterministic, multitasking [[Kernel (operating system)|kernel]] for [[microprocessor]]s, and [[digital signal processor]]s (DSPs). It manages up to 255 application64 tasks. Its size can be scaled (between 5 and 24 Kbytes) to only contain the features needed for a given use.

Most of μC/OS-II is written in highly portable [[ANSI C]], with target microprocessor-specific code written in [[assembly language]]. Use of the latter is minimized to ease [[porting]] to other processors.

=== Uses in embedded systems ===

μC/OS-II was designed for embedded uses. If the producer has the proper tool chain[[toolchain]] (i.e., C compiler, assembler, and linker-locator{{clarify|date=May 2024}}), μC/OS-II can be embedded as part of a product.

μC/OS-II is used in many embedded systems, including:

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*Waiting (for an event)

*Interrupted ([[Interrupt handler|interrupt service routine]] (ISR))

Further, it can manage up to 25564 tasks. However, it is recommended that eight of these tasks be reserved for μC/OS-II, leaving an application up to 24756 tasks.<ref>{{cite book|last=Labrosse|first=Jean J.|title=MicroC/OS-II: The Real Time Kernel|page=77|edition=Second2nd}}</ref>

===Kernels===

The [[Kernel (operating system)|kernel]] is the name given to the program that does most of the housekeeping tasks for the operating system. The boot loader hands control over to the kernel, which initializes the various devices to a known state and makes the computer ready for general operations.<ref>[[Wikiversity:Operating Systems/Kernel Models#Monolithic Kernel]]</ref> The kernel is responsible for managing tasks (i.e., for managing the CPU's time) and communicating between tasks.<ref>{{cite book|last=Labrosse|first=Jean J.|title=MicroC/OS-II: The Real Time Kernel|page=39|edition=Second2nd}}</ref> The fundamental service provided by the kernel is [[context switch]]ing.

The [[scheduler]] is the part of the kernel responsible for determining which task runs next.<ref name="LabrosseP40">{{cite book|last=Labrosse|first=Jean J.|title=MicroC/OS-II: The Real Time Kernel|page=40|edition=Second2nd}}</ref> Most real-time kernels are priority based. In a priority-based kernel, control of the CPU is always given to the highest priority task ready to run. Two types of priority-based kernels exist: [[Computer multitasking#Cooperative multitasking|non-preemptive]] and [[Preemption (computing)|preemptive]]. Nonpreemptive kernels require that each task do something to explicitly give up control of the CPU.<ref name="LabrosseP40" /> A preemptive kernel is used when system responsiveness is more important. Thus, μC/OS-II and most commercial real-time kernels are preemptive.<ref>{{cite book|last=Labrosse|first=Jean J.|title=MicroC/OS-II: The Real Time Kernel|page=42|edition=Second2nd}}</ref> The highest priority task ready to run is always given control of the CPU.

===Assigning tasks===

Tasks with the highest rate of execution are given the highest priority using [[rate-monotonic scheduling]].<ref>{{cite journal|last1=Liu|first1=Chung Lang|last2=Layland|first2=James W.|title=Scheduling algorithms for multiprogramming in a hard real-time environment|journal=Journal of the ACM |volume=20|issue=1|pages=46–61|doi=10.1145/321738.321743|year=1973|citeseerx=10.1.1.36.8216|s2cid=59896693 }}</ref> This scheduling algorithm is used in real-time operating systems (RTOS) with a [[static-priority scheduling class]].<ref>{{cite web|last1=Bovet |first1=Daniel |title=Understanding The Linux Kernel |url=http://oreilly.com/catalog/linuxkernel/chapter/ch10.html#85347 |url-status=dead |archiveurl=https://web.archive.org/web/20140921000832/http://oreilly.com/catalog/linuxkernel/chapter/ch10.html |archivedate=2014-09-21 }}</ref>

===Managing tasks===

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*Change a task's priority

*Suspend and resume a task

*Get information about a task<ref>{{cite book|last=Labrosse|first=Jean J.|title=MicroC/OS-II: The Real Time Kernel|pages=45–49|edition=Second2nd}}</ref>

===Managing memory===

To avoid [[Fragmentation (computing)|fragmentation]], μC/OS-II allows applications to obtain fixed-sized memory blocks from a [[Memory management (operating systems)#Partitioned allocation|partition]] made of a contiguous memory area. All memory blocks are the same size, and the partition contains an [[integral]] number of blocks. Allocation and deallocation of these memory blocks is done in constant time and is a [[deterministic system]].<ref>{{cite book|last=Labrosse|first=Jean J.|title=MicroC/OS-II: The Real Time Kernel|pages=273–285|edition=Second2nd}}</ref>

===Managing time===

μC/OS-II requires that a periodic time source be provided to keep track of time delays and timeouts. A tick should occur between 10 and 1000 times per second, or [[Hertz]]. The faster the tick rate, the more [[Overhead (computing)|overhead]] μC/OS-II imposes on the system. The frequency of the clock tick depends on the desired tick resolution of an application. Tick sources can be obtained by dedicating a hardware timer, or by generating an [[interrupt]] from an [[alternating current]] (AC) power line (50 or 60&nbsp;Hz) signal. This periodic time source is termed a clock tick.<ref>{{cite book|last=Labrosse|first=Jean J.|title=MicroC/OS-II: The Real Time Kernel|pages=145–152|edition=Second2nd}}</ref>

After a ''clock tick'' is determined, tasks can be:

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===Task states===

μC/OS-III is a [[Computer multitasking|multitasking]] operating system. Each task is an infinite loop and can be in any one of five states (dormant, ready, running, interrupted, or pending). TaskμC/OS-III prioritiessupports canan rangeunlimited fromnumber 0of (highesttask priority)priorities but configuring μC/OS-III to ahave maximumbetween of32 255and (lowest256 possibletask priority)priorities typically suits most embedded systems well.<ref>https://media.digikey.com/PDF/Data%20Sheets/Micrium%20PDFs/UC_OS-III_RTOS.pdf#:~:text=Micrium%E2%80%99s%20%CE%BCC%2FOS-III%20supports%20ARM7%2F9%2C%20Cortex-MX%2C%20Nios-II%2C%20PowerPC%2C%20Coldfire%2C,are%20available%20for%20download%20from%20the%20Micrium%20website. {{Bare URL inline|date=August 2025}}</ref>

===Round robin scheduling===

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===Managing tasks===

Task management also functions the same as for μC/OS-II,. howeverHowever, μC/OS-III supports multitasking and allows an application to have any number of tasks. The maximum number of tasks is limited by only the amount of [[Computercomputer memory|memory]] (both code and data space) available to the processor.

A task can be implemented via [[runviarunning to scheduled completion scheduling]], in which the task deletes itself when it is finished, or more typically as an [[infinite loop]], waiting for events to occur and processing those events.

===Managing memory===

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Sometimes, a task or ISR must communicate information to another task, because it is ''unsafe'' for two tasks to access the same specific data or hardware resource at once. This can be resolved via an information transfer, termed inter-task communication. Information can be communicated between tasks in two ways: through global data, or by sending messages.

When using global variables, each task or ISR must ensure that it has exclusive access to variables. If an ISR is involved, the only way to ensure exclusive access to common variables is to disable [[interrupt]]s. If two tasks share data, each can gain exclusive access to variables by either disabling interrupts, locking the scheduler, using a [[Semaphore (programming)|semaphore]], or preferably, using a [[mutual exclusion]] semaphore. Messages can be sent to either an intermediate object called a [[message queue]], or directly to a task, since in μC/OS-III, each task has its own built-in message queue. Use an external message queue if multiple tasks are to wait for messages. Send a message directly to a task if only one task will process the data received. While a task waits for a message to arrive, it uses no CPU time.

==Ports==

A port involves three aspects: CPU, OS, and board specific (BSP) code. μC/OS-II and μC/OS-III have ports for most popular processors and boards in the market and are suitable for use in [[safety critical]] embedded systems such as aviation, medical systems, and nuclear installations. A μC/OS-III port involves writing or changing the contents of three kernel specific files: <code>OS_CPU.H</code>, <code>OS_CPU_A.ASM</code>, and <code>OS_CPU_C.C</code>. It is necessary to write or change the content of three CPU specific files: <code>CPU.H</code>, <code>CPU_A.ASM</code>, and <code>CPU_C.C</code>. Finally create or change a board support package (BSP) for the evaluation board or target board being used. A μC/OS-III port is similar to a μC/OS-II port. There are significantly more ports than listed here, and ports are subject to continuous development. Both μC/OS-II and μC/OS-III are supported by popular [[Transport Layer Security|SSL/TLS]] libraries such as [[wolfSSL]], which ensure security across all connections.

==Licensing Change==

After acquisition by Silicon Labs, Micrium in 2020 has changed to an Open Source licensing model in February 2020. This includes uC/OS III, all prior versions, all components (USB, file system, GUI, TCP/IP, etc).

==Licensing Changechange==

After acquisition by Silicon Labs, Micrium in 2020 has changed to an[[open-source Open Sourcemodel]] licensing model in February 2020. This includes uC/OS III, all prior versions, all components: (USB, [[file system]], GUI, TCP/IP, etc).

==Documentation and Supportsupport==

InSupport additionis toavailable via a typical support forum, aand numberseveral comprehensive books, of well-writtenwhich bookssome are available.tailored Booksto area availablegiven microcontroller architecture and development platform, as free PDFs, or foras low-cost purchase asin hard-cover books. APaid numbersupport ofis booksavailable arefrom eachWeston tailoredEmbedded to a particular microcontroller architecture / development platformSolutions.

Paid support is available from Micrium and others.

==References==

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==External links==

*{{Official website|https://web.archive.org/web/20231206170818/https://www.micriumsilabs.com/productsdevelopers/micrium}}

*{{githubGitHub|SiliconLabs}}

*[httphttps://people.ece.cornell.edu/land/courses/ece5760/NiosII_muCOS/uC_Functions.html Summary of Commonly Used uC/OS-II Functions and Data Structures]

*[httphttps://people.ece.cornell.edu/land/courses/ece5760/NiosII_muCOS/ NiosII GCC with MicroC/OS]

*[http://www.farnell.com/datasheets/1950186.pdf μC/OS-II Reference Manual]

*[http://ftp1.digi.com/support/documentation/0220047_e.pdf How to Get a μC/OS-II Application Running]