RTOSX KERNEL Real-Time
Operating System

Industrial Grade Alternative to Eclipse ThreadX

X KERNEL symbol

Reimagined by Bill Lamie, RTOSX KERNEL is the Industrial Grade alternative to Eclipse ThreadX. It was originally derived from the Eclipse ThreadX source code, refactored and infused with some of the advanced technology of the PX5 RTOS. It is 100% API compatible with existing THREADX applications and still is one of the smallest RTOS, ideal for memory-constrained devices:

  • RTOSX KERNEL requires less than 3KB of flash memory
  • RTOSX KERNEL requires less than 3KB of RAM

RTOSX KERNEL delivers sub-microsecond context switching and API calls on most microprocessors for ultra-high performance.

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

RTOSX KERNEL also enables best-in-class safety and security for your embedded applications.

  • The entire RTOSX KERNEL code base is 100% C statement and branch decision coverage for every release.
  • The RTOSX KERNEL offers Pointer/Data Verification (PDV) technology for unprecedented run-time function pointer, system object, buffer, and stack verification. This advanced technology is from the PX5 RTOS.
  • Central error handling technology from PX5 RTOS.
  • 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).
  • MISRA-C:2004 and MISRA C:2012 Compliant
  • Functional Safety Certified (highest level of IEC 61508 standard)

For even more safety and security, memory protection for RTOSX KERNEL applications is available through RTOSX Modules, which provide a lightweight infrastructure of separately built C application modules to guard execution by MPU and MMU facilities.

Highly Evolved:
RTOSX KERNEL Leading the Next Generation of Real-Time Operating System

RTOSX KERNEL IS INDUSTRIAL GRADE

RTOSX KERNEL is Bill Lamie’s Industrial Grade alternative to Eclipse ThreadX, which is also one of the most widely used RTOS-with over 10 billion deployments. Bill is also the author of Nucleus PLUS, Nucleus RTX, and the most advanced PX5 RTOS.

This is one of the best RTOS for MCUs and MPUs from AMD, GigaDevice, NXP Semiconductors, Renesas, SiFive, STMicroelectronics, and Texas Instruments.

Components of RTOSX KERNEL

Mouse over for component details
RTOSX KERNEL API
RTOSX KERNEL Services Message Queues Counting Semaphores Mutexes Event Flags Block Memory Pools Byte Memory Pools Application Timers
RTOSX KERNEL Core Scheduler
  • Small
  • Fast
  • Advanced
  • Deterministic
  • Simple
  • Safe and Secure
  • Popular THREADX API
  • Pointer/Data Verification
  • Highly Portable
  • Reasonable Licensing
  • No Royalties
  • Full Source Code
  • Professional Support

Most Deployed RTOS — over 10 billion THREADX deployments

As of 2021, THREADX has been deployed in over 10 billion devices, making it one of the most widely relied upon RTOS. RTOSX KERNEL fully leverages the field-proven THREADX code base.

We have followed the growth trajectory of THREADX in the wireless and IoT markets since the company’s founding, and are increasingly impressed by the widespread industry adoption of THREADX.

— Chris Rommel, Executive Vice President, VDC Research
SMALL
SAFE
SECURE
ADVANCED
FAST
EASY

Fast & Deterministic

RTOSX KERNEL 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 entirely 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

RTOSX KERNEL is one of the smallest embedded RTOS, requiring less than 3KB of flash memory and 3KB 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 RTOSX KERNEL complies with IEC-61508 SIL 4 (electronic), IEC 62304 Class C (medical), ISO 26262 ASIL D (automotive), and EN 50128 (rail) functional safety standards. RTOSX KERNEL is suitable for developing safety-critical software to the highest integrity levels (SIL 4).

Simple, two main source files

RTOSX KERNEL comprises two main source files: rtosx.c and rtosx_binding.s. Drop these RTOSX KERNEL files into any C main project example, and RTOSX KERNEL will almost be ready to run. There are no complicated projects or linker control file changes.

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

RTOSX KERNEL is 100% API compatible with applications written for THREADX

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 RTOSX KERNEL binding layer source.
  • The RTOSX KERNEL source code is designed to be easily understood.
  • The RTOSX KERNEL 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.

PORTABLE RTOS

Most of RTOSX KERNEL is written in ANSI C, making it highly portable to any processor architecture with C compiler support. 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 RTOSX KERNEL supports the most popular embedded development tools, including those from IAR, Arm, and GCC.

Professional Support

The embedded RTOSX experts on the RTOSX KERNEL support team are always ready to help and promise quick action on every request. Unlike many open-source and commercial RTOS, RTOSX KERNEL support is available when needed. We are here to help!

Support

Royalty Free

RTOSX KERNEL offers royalty-free licensing. Like the product, RTOSX KERNEL licensing is simple and easy to work with. Please get in touch with us for more information!

THE ADVANCED RTOSX KERNEL

RTOSX KERNEL Snapshot

  • Industrial Grade alternative to Eclipse ThreadX
  • Industry Leader
  • Over 10 Billion Deployments
  • Small-footprint
  • Fast, deterministic execution
  • Simple, easy-to-use
  • Advanced technology
  • Multicore support (AMP & SMP)
  • Memory Protection via RTOSX MODULES
  • Fastest Time-To-Market
  • Royalty Free
  • Full, highest-quality source code
  • Pre-certified by TUV and UL to IEC 61508 SIL 4, IEC 62304 Class C, ISO 26262 ASIL D, and EN 50128 SW-SIL 4.
  • MISRA-C:2004 and MISRA C:2012 Compliant

Supported Architecture

  • Arm
    Cortex-M, Cortex-R, Cortex-A
    Cortex-Axx 64-bit
    TrustZone ARMv8-M
  • Cadence Xtensa
    Diamond
  • MIPS MIPS32 4Kx, 24Kx, 34Kx 1004K
    microAptiv, interAptiv, proAptiv
  • PowerPC
  • Renesas RX
  • RISC-V 32-bit
    64-bit
  • Synopsys ARC EM
    ARC HS

Why Choose RTOSX KERNEL

RTOSX KERNEL is a robust, industrial-grade alternative to Eclipse ThreadX, fully API-compatible and requiring no code changes for migration. Infused with PX5 RTOS technology like Pointer/Data Verification (PDV) and centralized error handling, RTOSX KERNEL still maintains a small footprint, full multithreading, and hard real-time performance. It includes full tool support, source code, and royalty-free licensing, ensuring security and faster time to market for safety-critical and non-safety-critical devices.

RTOSX KERNEL Eclipse ThreadX
ThreadX Compatible 100% 100%
Safety-Certified Version Version 7.0.0 (2025) Version 6.1.1 (2020)
Source Code Distribution Refactored, simplified 2 file distribution Over 100 files; developer must pull together
Cross Function Optimization check mark not available
Advanced Features
Pointer/Data Verification [1] check mark  (from PX5 RTOS) not available
Central Error Handling check mark  (from PX5 RTOS) not available
Documentation
ThreadX User Guide PDF User Guide On-line docs on GitHub
Processor/Tool User Guide check mark not available
Quickstart Guide check mark not available
Programmer’s Reference Card check mark not available
Support
Support & Maintenance Professionally maintained and supported Community
IP Protection Full Indemnification not available

[1] Optional Pointer/Data Verification (PDV) checks integrity at run-time of RTOS global data area, object control blocks, allocated memory, and thread stacks.

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THREADX History

The Evolution of
THREADX

THREADX has a rich history spanning over two decades. Introduced commercially in 1997, it has evolved significantly, achieving over 10 billion deployments by 2021. THREADX is one of the most widely used RTOSes globally, powering devices from smartphones to automotive applications.

Learn THREADX History

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Latest RTOS

PX5 RTOS Introducing the advanced 5th generation PX5 RTOS with native POSIX pthreads+ support.

Should your project require cutting-edge RTOS technology or the sharing of code between an embedded Linux project and a deeply embedded one, the PX5 RTOS, designed for industrial-grade applications, provides the ideal solution.

Explore PX5 RTOS

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This site may contain content from Microsoft Corporation under an MIT license. Here is the necessary MIT license information:   Copyright ©  Microsoft Corporation
This program and the accompanying materials are made available under the terms of the MIT License which is available at https://opensource.org/licenses/MIT.   SPDX-License-Identifier: MIT

ThreadX, GUIX, FileX, NetX Duo, and USBX are registered trademarks of the Eclipse Foundation.

RTOSX, RTOSX KERNEL, RTOSX FILE, RTOSX NET, and RTOSX USB are trademarks of PX5.

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