The table below shows the evolution of µC/OS over the years, comparing the features available in each version.
Feature | µC/OS | µC/OS-II | µC/OS-III |
|---|---|---|---|
Year introduced | 1992 | 1998 | 2009 |
Book | Yes | Yes | Yes |
Source code available | Yes | Yes | Yes |
Preemptive Multitasking | Yes | Yes | Yes |
Maximum number of tasks | 64 | 255 | Unlimited |
Number of tasks at each priority level | 1 | 1 | Unlimited |
Round Robin Scheduling | No | No | Yes |
Semaphores | Yes | Yes | Yes |
Mutual Exclusion Semaphores | No | Yes | Yes (Nestable) |
Event Flags | No | Yes | Yes |
Message Mailboxes | Yes | Yes | No (not needed) |
Message Queues | Yes | Yes | Yes |
Fixed Sized Memory Management | No | Yes | Yes |
Signal a task without requiring a semaphore | No | No | Yes |
Option to Post without scheduling | No | No | Yes |
Send messages to a task without requiring a message queue | No | No | Yes |
Software Timers | No | Yes | Yes |
Task suspend/resume | No | Yes | Yes (Nestable) |
Deadlock prevention | Yes | Yes | Yes |
Scalable | Yes | Yes | Yes |
Code Footprint | 3K to 8K | 6K to 26K | 6K to 24K |
Data Footprint | 1K+ | 1K+ | 1K+ |
ROMable | Yes | Yes | Yes |
Run-time configurable | No | No | Yes |
Compile-time configurable | Yes | Yes | Yes |
ASCII names for each kernel object | No | Yes | Yes |
Pend on multiple objects | No | Yes | Yes |
Task registers | No | Yes | Yes |
Built-in performance measurements | No | Limited | Extensive |
User definable hook functions | No | Yes | Yes |
Time stamps on posts | No | No | Yes |
Built-in Kernel Awareness support | No | Yes | Yes |
Optimizable Scheduler in assembly language | No | No | Yes |
Catch a task that returns | No | No | Yes |
Tick handling at task level | No | No | Yes |
Source code available | Yes | Yes | Yes |
Number of services | ~20 | ~90 | ~70 |
MISRA-C:1998 | No | Yes (except 10 rules) | N/A |
MISRA-C:2004 | No | No | Yes (except 7 rules) |
DO178B Level A and EUROCAE ED-12B | No | Yes | In progress |
Medical FDA pre-market notification (510(k)) and pre-market approval (PMA) | No | Yes | In progress |
SIL3/SIL4 IEC for transportation and nuclear systems | No | Yes | In progress |
IEC-61508 | No | Yes | In progress |
Table 1-1 µC/OS, µC/OS-II and µC/OS-III Features Comparison Chart