The table below shows the evolution of µC/OS over the years, comparing the features available in each version.
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| Table - 1-1 µC/OS, µC/OS-II and µC/OS-III Features Comparison Chart |
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| Table - 1-1 µC/OS, µC/OS-II and µC/OS-III Features Comparison Chart |
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| title | Table - 1-1 µC/OS, µC/OS-II and µC/OS-III Features Comparison Chart |
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| Feature | µC/OS | µC/OS-II | >µC/OS-III |
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| 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/Signal 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 (i.e. Wait) on multiple objects | No | Yes | Yes | | Task registers | No | Yes | Yes | | Built-in Kernel Awareness support | No | Yes | Yes | | Built-in performance measurements | No | Limited | Extensive | | Built-in trace points | No | No | Yes | | User definable hook functions | No | Yes | Yes | | Time stamps on posts |
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| Yes | | Optimizable Scheduler in assembly language | No | No | Yes | | Catch a task that returns | No | No | Yes | | Tick handling at task level | No |
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| Yes | Yes | | Source code available | Yes | Yes | Yes | | Number of services | ~20 | ~90 |
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| | DO178B Level A and EUROCAE ED-12B | No | Yes |
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| Yes | | Medical FDA pre-market notification (510(k)) and pre-market approval (PMA) | No | Yes | Yes | | Medical IEC-62304 | No | Yes |
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| IEC for transportation and nuclear systems | No | Yes |
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