Last modified on Sat Jul 22 11:30:02 2023 UTC.   Improve this page


The µOS++ APIs implement a portable, vendor-independent hardware abstraction layer intended for embedded applications, but designed with special consideration for the industry standard ARM Cortex-M processor series.


The µOS++ components are:

  • µOS++ Core - C++ API and implementation for the Cortex-M processors core and peripherals;
  • µOS++ Startup - portable C/C++ API and implementation for the processor startup code, replacing non-portable vendor assembly code;
  • µOS++ RTOS APIs - a collection of C++ and C APIs for Real-Time operating systems, based on a POSIX inspired C++ layer;
  • µOS++ ISO Standard Threads - an implementation of the C++ Standard ISO/IEC 14882:2011(E) Thread library, on top of the µOS++ RTOS threads;
  • µOS++ Drivers - defines generic peripheral driver interfaces for middleware making it reusable across supported devices
  • µOS++ POSIX I/O - a compatibility layer bringing together access to terminal devices, files and sockets, via a unified and standard API;
  • µOS++ Diagnostics - a C++/C API providing support for diagnostics and instrumentation.


Although designed with both the 32-bits Cortex-M architectures and the arm-none-eabi-gcc compiler in mind, most µOS++ components are highly portable and can be compiled with any ISO C++ 11 compiler for other platforms too, for example the µOS++ RTOS can run on 64-bits Intel based POSIX desktops, greatly improving components testability.


In µOS++ IIIe, the APIs were called CMSIS++, which were created both as a proposal for a future CMSIS, and to overcome the limitations/problems of the current CMSIS design, among them the lack of proper C++ support.

The original ARM Keil name stands for Cortex Microcontroller Software Interface Standard, and the CMSIS++ design inherits the good things from ARM CMSIS but goes one step further into the world of C++; it is not a C++ wrapper on top of ARM CMSIS, but a completely new design in C++, with several C APIs as wrappers on top of the native C++ APIs.

In µOS++ IVe, the name CMSIS was dropped.


The µOS++ APIs are provided free of charge under the terms of the MIT License.

This means you can use µOS++ in any commercial or open source projects without any limitations except preserving the included copyright notice.