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µC/OS-III is a highly portable, ROMable, scalable, preemptive, real-time, deterministic, multitasking kernel for microprocessors, microcontrollers and DSPs.

Offering unprecedented ease-of-use, μC/OS-III is delivered with complete 100% ANSI C source code and in-depth documentation. μC/OS-III runs on the largest number of processor architectures, with ports available for download from the Micrium Web site.

µC/OS-III manages an unlimited number of application tasks, constrained only by a processor’s access to memory. µC/OS-III also supports an unlimited number of priority levels (typically configured for between 8 and 256 different priority levels).

µC/OS-III allows for unlimited tasks, semaphores, mutexes, event flags, message queues, timers and memory partitions. The user allocates all kernel objects at run time. µC/OS-III provides features to allow stack growth of tasks to be monitored. While task size is not limited, they need to have a minimum size based on the CPU used.

µC/OS-III allows multiple tasks to run at the same priority level. When equal priority tasks are ready-to-run, µC/OS-III runs each for a user-specified amount of time. Each task can define its own time quanta and give up its time slice if it does not require the full time quanta.

µC/OS-III provides extensive range checking which can be disabled at compile time.  µC/OS-III thus checks for NULL pointers passed in API calls, task level services from ISRs aren’t called, arguments are within allowable range, and specified options are valid. Each API function provides an error code regarding the outcome of the function call.

µC/OS-III’s footprint can be scaled to contain only the features required for a specific application (typically 6–24 KBytes of code space residing in memory).


The features of µC/OS-III include:

  • Preemptive multitasking real-time kernel with optional round robin scheduling
  • Delivered with complete, clean, consistent, 100% ANSI C source code with in-depth documentation.
  • Mutual exclusion semaphores with built-in priority inheritance protocol to prevent priority inversions
  • Timeouts on ‘pend’ calls to prevent deadlocks
  • Unlimited number of tasks, priorities and kernel objects
  • Highly scalable (6K to 24K bytes code space, 1K+ bytes data space)
  • Very Low Interrupt Disable Time
  • Extensive performance measurement metrics (configurable)
  • Third party certifiable

Multi-threaded applications

µC/OS-III allows developers to produce multi-threaded applications, vital to the development of safety-critical systems. Thanks to improved integration with IAR Embedded Workbench for ARM, developers can access all the inherent non-reentrant features of C/C++ in a thread-safe manner.

Application developers who write code for use in multi-threaded environments will find the support critical when protecting shared objects using system locks, file-stream locks, and thread-local storage (TLS) in multi-threaded environments.

Micrium and IAR collaborated in providing the first thread-safe support in µC/OS-III for the IAR DLIB run-time library. Protection for such non-reentrant functions as strtok(), rand(), errno() and more are local to each thread. Global and static variables typically used by these functions are protected by the Micrium kernel.

Supported processors

See the complete list of available ports in the ´Workks With´ tab

  • FPU (Floating-Point Unit) Support
  • MPU (Memory Protection Unit) Support - Call.
  • MMU (Memory Management Unit) Support - Call


Multicore support

  • µC/OS-III has full multicore support.
  • AMP (Assymetrical Multi Processing)
  • SMP (Symmetrical Multi Processing) can be made available


Multitasking model

  • µC/OS-III supports preemptive multitasking.
  • Unlimited maximum number of Tasks
  • Optional Round-Robin Scheduling
  • Unlimited number of tasks at each priority
  • Clear stack at task creation (optional per-task)
  • Run-time stack checking (optional)
  • Catch/delete task that return
  • Reentrant libraries (support of Thread Local Storage for compiler)
  • Unlimited Task registers
  • Tick rate - Configurable (Typ. 1 to 100 ms)


ISR stack

Micrium provides an optional ISR stack for µC/OS-III.

  • User definable hooks
  • Task switch hook
  • Idle task hook
  • Statistic task hook
  • Create task hook
  • Delete task hook
  • Catch task return hook
  • Initialization hook



Memory footprint for µC/OS-III:

  • ROMable
  • Scalable (compile and run-time configurable)
  • ROM (Min-Max) 6K-24K (bytes)
  • RAM 1K+ (bytes)


ANSC-C source

µC/OS-II is provided as clean and highly consistent ANSI-C source code.

  • Number of source files    Fewer than 25
  • Argument checking (optional)
  • ASCII names for kernel objects
  • MISRA-C:2004 rules (most)


Kernel services

µC/OS-III provides approximately 80 API calls.

  • Timeout on calls (prevents deadlocks)
  • Semaphores (unlimited)
  • Task semaphore
  • Event Flags (unlimited)
  • Mutual Exclusion Semaphores (full priority inheritance and nestable)
  • Message queues (unlimited)
  • Task message queue (optional)
  • Memory partitions (prevents fragmentation)
  • Software timers (unlimited)
  • Task suspend/resume
  • Lock/Unlock scheduler
  • Pend on multiple objects (optional)


Built-in performance measurements

Micrium provides optional built-in performance measurements.

  • Maximum interrupt disable time
  • Maximum scheduler lock time
  • Per-Task maximum interrupt disable time
  • Per-Task maximum scheduler lock time
  • Per-Task CPU usage (%)
  • Total CPU usage (%)
  • Per-Task stack usage
  • Per-Task run counter
  • Message pool statistics
  • Context switch counter
  • Debugger Kernel Awareness Support


Third-party certifications

µC/OS-III is certified for:

  • Avionics, DO178B - Call
  • Medical, FDA 510(k) - Call
  • Industrial, IEC61508


Debugger kernel awareness support

µC/OS-III includes support for Kernel Awareness.

  • µC/Probe - Graphical Live Watch
  • IAR
  • Atollic
  • Call for others.


User Manual