Differences Between μC/OS, μC/OS-II, and μC/OS-III

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Differences Between μC/OS, μC/OS-II, and μC/OS-III

Editor | strongerHuang

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uC/OS can be considered a classic RTOS, early on when we searched for RTOS learning resources online, most of the information was about uC/OS, and there was little mention of other RTOS (other RTOS, such as FreeRTOS, RT-Thread, etc., became popular later).
Here we share the differences among μC/OS, μC/OS-II, and μC/OS-III:

Features

uC/OS

uC/OS-II

uC/OS-III

Year of Birth

1992

1998

2009

Books

Yes

Yes

Yes

Source Code Provided

Yes

Yes

Yes

Preemptive Multitasking

Yes

Yes

Yes

Max Task Count

64

256

Unlimited

Task Count per Priority

1

1

Unlimited

Time-Slicing

No

No

Yes

Semaphore

Yes

Yes

Yes

Mutex Semaphore

No

Yes

Yes (Nested)

Event Flag

No

Yes

Yes

Message Mailbox

Yes

Yes

No (Not Needed)

Message Queue

Yes

Yes

Yes

Fixed Size Memory Management

No

Yes

Yes
Mark a Task Without Semaphore
No
No
Yes
Send Message to Task Without Message Queue
No
No
Yes
Software Timer
No
Yes
Yes
Task Stop/Resume
No
Yes
Yes (Nested)
Deadlock Prevention
Yes
Yes
Yes
Scalable
Yes
Yes
Yes
Code Segment Requirement
3K to 8K
6K to 26K
6K to 20K
Data Segment Requirement
1K+
1K+
1K+
Can Be Made Static
Yes
Yes
Yes
Runtime Configuration
No
No
Yes
Compile Time Configuration
Yes
Yes
Yes
Object Naming
No
Yes
Yes
Pause Multiple Objects
No
Yes
Yes
Task Register
No
Yes
Yes
Embedded Measurement Function
No
Limited
Abundant
User Defined Hook Functions
No
Yes
Yes
Timestamp
No
No
Yes
Embedded Kernel Debugging
No
Yes
Yes
Assembly Optimization
No
No
Yes
Task Level Timer Handling
No
No
Yes
Services Provided
~20
~90
~70
MISRA-C:1998
No
Yes (Except 10 Rules)
N/A
MISRA-C:2004
No
No
Yes (Except 7 Rules)
DO178BEUROCAE ED-12B
No
Yes
Applying
FDA Certification
No
Yes
Applying
SIL3/SIL4 IEC
No
Yes
Applying
IEC-61508
No
Yes
Applying
The uC/OS operating system was initially commercial software, but after being acquired by Silicon Labs, its kernel source code and components became free and open source software.
The article “The Story of the Embedded Operating System µC/OS” mentions some stories about the development history of µC/OS.
Disclaimer: The materials in this article are sourced from the internet, and the copyright belongs to the original author. If there are any copyright issues, please contact me for removal.
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