PX5 RTOS is smaller, faster, deterministic and certified

The RTOS of choice for professional developers

PX5 RTOS is one of the smallest RTOS, ideal for memory-constrained embedded devices:

  • The RTOS requires sub-1KB of flash memory.
  • The RTOS only needs 1KB of RAM on typical 32-bit microcontrollers.
The RTOS delivers sub-microsecond context switching and API calls on most microprocessors for ultra-high performance.

Rich determinism makes the RTOS ideal for the most demanding real-time embedded applications.

The RTOS also enables best-in-class safety and security for your embedded applications.

  • PX5 tests the entire RTOS code base with complete C statement and branch decision coverage for every release.
  • The RTOS offers pointer/data verification (PDV) technology for unprecedented run-time function pointer, system object, buffer, and stack verification.
  • The RTOS is certified to the industry functional safety standards IEC 61508 SIL 4 (electronic), IEC 62304 Class C (medical), ISO 26262 ASIL D (automotive), and EN 50128 SW-SIL 4 (rail).
For even more safety and security, memory protection for RTOS applications is available through PX5 MODULES, which provides a lightweight infrastructure of separately built C application modules to guard execution by MPU and MMU facilities.

An API that is a native implementation of the POSIX pthreads standard enables portability with embedded Linux and other POSIX RTOSes, making the RTOS among the simplest to use. Optional extensions make this the best RTOS for deeply embedded, real-time applications.

PX5 RTOS is Bill Lamie’s fifth generation and best RTOS. The list of RTOSes authored by Bill include ThreadX, Nucleus PLUS, and Nucleus RTX—three of the most popular RTOSes used in billions of devices worldwide.

This is the best RTOS for use with boards from AMD, GigaDevice, NXP Semiconductors, Renesas, SiFive, STMicroelectronics, and Texas Instruments.

Get a Free RTOS Download for Evaluation

The Industrial Grade PX5 RTOS is an advanced, 5th generation RTOS designed for the most demanding embedded applications.

Components of PX5 RTOS

Mouse over for component details
PX5 RTOS C Implementation (px5.c) PX5 RTOS Binding Layer (px5_binding.s)
  • Small & fast RTOS
  • Fifth-generation RTOS by the author of ThreadX and Nucleus
  • Deterministic RTOS
  • Easy to use RTOS
  • Safe and secure RTOS
  • Memory protection via PX5 MODULES
  • Pre-certified RTOS to highest IEC 61508 SILs for safety
  • POSIX RTOS with native pthread API
  • Pointer/data verification (PDV)
  • Asymmetric multiprocessing (AMP)
  • Symmetric multiprocessing (SMP)
  • Cortex-M/R/A RTOS
  • Arm 64-bit RTOS
  • Renesas RX RTOS
  • IAR, GCC, Arm tools
  • Full source code
  • Royalty-free RTOS
  • Professional Support

Fast and deterministic

PX5 RTOS is extremely fast and efficient. On typical 32-bit microcontrollers running at 80MHz, most API calls and context switches complete in less than one microsecond. It’s also a deterministic RTOS: The processing for each API and context switch is completely predictable and not a function of the number of active threads. For example, the processing required to obtain a semaphore is the same whether two or 100 threads are active.

One of the smallest RTOS

This is one of the smallest embedded RTOSes, requiring less than 1KB of flash memory and 1KB of RAM on typical 32-bit microcontrollers. Implemented with loosely coupled C functions, RTOS size scales automatically based on the application's use. The linker does not bring APIs and associated functions into the image unless they are used.

Safety-certified RTOS

SGS-TUV SaarSGS-TUV Saar pre-certifies that PX5 RTOS complies with IEC-61508 SIL 4 (electronic), IEC 62304 Class C (medical), ISO 26262 ASIL D (automotive), and EN 50128 (rail) functional safety standards. PX5 RTOS is suitable for developing safety-critical software to the highest integrity levels (SIL 4).

Simple — two main source files

The RTOS is composed of two main source files: px5.c and px5_binding.s. Drop these RTOS files into any C main project example, and PX5 is ready to run. No complicated projects and/or linker control file changes.

Using PX5 in an application is also easy: Simply include POSIX pthread.h and add a call to px5_pthread_start to your C main function, as follows:

#include <pthread.h>

int    main()

  /* Start PX5.  */ 
  px5_pthread_start(1, NULL, 0);

  /* Once px5_pthread_start returns, the C main function
     has been elevated to a thread - the first thread in
     your system!  */

     /* PX5 RTOS API calls are all available at 
        this point. For this example, simply sleep for 
        1 second.  */

PX5 RTOS is easy to install and use, taking only a few minutes. Use the processor-to-tool binding layer examples as a starting point.

Native POSIX pthreads API support simplifies development.

  • This Linux RTOS-compatible API reduces the learning curve for Linux developers new to embedded RTOS.
  • POSIX-compatibility enables code sharing between devices that run embedded Linux.

Advanced technology

  • Data encapsulation technology assists compilers in generating the smallest, fastest code and reduces namespace collision with the application.
  • Pointer/Data Verification (PDV) technology, a next-generation embedded RTOS technology, enables unprecedented verification of run-time function pointers, linked lists, and stacks.
  • Central error handling - with optional user enhancement - helps facilitate building more robust applications.

Full source code

  • You receive complete source code, including the RTOS binding layer source.
  • The RTOS source code is designed to be easily understood.
  • The RTOS source code is rigorously tested: complete C statement and branch decision coverage testing for every release.
  • Discover the highest quality RTOS source on the market.


PX5 RTOS is written in ANSI C, making it highly portable to any processor architecture with C compiler support because 99%) of the RTOS is written in ANSI C. It supports popular embedded MCU and MPU architectures, including ARM Cortex-M, Cortex-R, Cortex-A, and RISC-V architecture families.

IAR, Arm & GCC tool support

As with its processor support, the PX5 RTOS supports the most popular embedded development tools, including those from IAR, Arm, and GCC.

Royalty-free RTOS

PX5 offers royalty-free licensing for the PX5 RTOS. Like the product itself, the PX5 RTOS licensing is simple and easy to work with.


Professional tech support

Always ready to help, the embedded RTOS experts on the PX5 support team promise quick action on every request. Unlike many open-source and some commercial RTOSes, RTOS support is available when you need it. We are here to help!



To take advantage of the advanced PX5 RTOS in your next embedded software design, please contact us about licensing options today!

Please also reach out to us if you have any questions about PX5 RTOS and how it might benefit your development.



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RTOS Tutorials

Watch our collection of RTOS tutorials to learn more about PX5 RTOS and how to write embedded software. Our video tutorials cover many RTOS topics, from installation and configuration to using advanced features. Our RTOS tutorials are produced by PX5 RTOS experts and are designed to be short, and informative.

Please let us know if you have any RTOS questions, comments, or suggestions – Enjoy!

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From PX5 Blog

Free PX5 RTOS Download Evaluations

Discover free PX5 RTOS evaluation packages for some of the most popular evaluation boards and development tools to see firsthand how PX5 RTOS can improve your embedded software development!

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